ISSN:0003-2654    

DOI:10.1039/AN99419FX001

出版商:RSC    

年代:1994

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN99419BX003

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Analyst, January 1994, Vol. 11 9 5N Conference Diary Date Conference Location 1994 February 13-17 Second International Glycobiology San Francisco, Symposium: Current Analytical Methods CA, USA 21-25 OFC '94: Optical Fibre Communications San Jose, CA, Conference USA 23-25 HTC 3: Third International Symposium on Antwerp, Hyphenated Techniques in Chromatography Belgium 2 8 4 3 Pittcon '94: The 45th Pittsburgh Conference on Chicago, Analytical Chemistry and Applied IL, Spectroscopy USA Contact Paddy Batchelder, P.O. Box 370, Pleasanton, CA 94566, USA Tel: + 1 510 426 9601. Fax: + 1 510 846 2242 Meetings Department, Optical Society of America, 2010 Massachusetts Avenue, NW, Washington, DC Tel: +1202 223 9034. Fax: +1 202 416 6100 Dr. R. Smits, p/a BASF Antwerpen N.V., Central Laboratory, Scheldelaan, B-2040 Antwerp, Belgium Tel: +32 3 568 2831.Fax: +32 3 568 3250 Mrs. Alma Johnson, Program Secretary, The Pittsburgh Conference, Department CFP, 300 Penn Center Boulevard, Suite 332, Pittsburgh, PA 15235, USA 20036-1023, USA March 7-11 4th International Symposium on Trends and Dresden, Frank Richter, TU Chemnitz, FB Physik, PSF 964, Fax: +49 371 852491 Rovisco Pais, 1096 Lisboa Codex, Portugal, or A. K. Tiller, Corrosion Centre, 23 Grosvenor Gardens, Kingston-upon-Thames, UK KT2 5BE, or D. Thierry, Swedish Corrosion Institute, Roslagsvagen 101, Hus 25, S-10405 Stockholm, Sweden New Applications in Thin Films Germany D-09009 Chemnitz, Germany 13-16 Third European Federation of Corrosion Estoril, CCsar Sequeira, Instituto Superior TCcnico, Av. Workshop on Microbial Corrosion Portugal 13-18 207th American Chemical Society National San Diego, CA, Department of Meetings, American Chemical Meeting USA Society, 1155-16th St., NW, Washington, DC 20036, USA Tel: +1 202 872 4396. Medical Branch, Box 55176, Galveston, TX 77555- Tel: + 1 409 770 6628 or 770 6605. Fax: + 1 409 770 6825 27-30 International Federation of Automatic Control Galveston, TX, IFAC Biomedical Symposium, University of Texas (IFAC) Symposium on Modeling and Control in Biomedical Systems 5176, USA USA April 6 8 Electroanalysis: A Tribute to Professor J.D. R. Cardiff, Dr. J. M. Slater, Department of Chemistry, Square, London, UK WClH OPP Tel: +44 71 380 7474. Fax: +44 71 380 7464 Technology, Mayfield House, 256 Banbury Road, Tel: +44 (0)865 512242. Fax: +44 (0)865 310981 Mr.B. R. Hodson, American Chemical Society, 1155-16th Street N.W., Washington, DC 20036, Tel: +1202 872 4396. Laboratories, P.O. Box 999, P7-35, Richland, WA Tel: + 1 509 376 2452. Fax: + 1 509 376 2373 Technology Conference, 24 Menlove Gardens North, Liverpool, UK L18 2EJ Tel: +44 51 737 1993. Fax: +44 51 737 1070 Thomas UK Birkbeck College, University of London, 29 Gordon 10-13 ANATECH 94: 4th International Symposium Mandelieu La ANATECH 94 Secretariat, Elsevier Advanced Napoule, on Analytical Techniques for Industrial Process Control France Oxford, UK OX2 7DH 10-15 207th ACS National Meeting and 5th Chemical Mexico City, Congress of North America (with Sessions of Analytical Chemistry, Environmental USA Chemistry, Chemical Health and Safety, etc.) Applications of Radioanalytical Chemistry Hawaii, Mexico 10-16 3rd International Conference on Methods and Kailua-Kona, Ned A Wogman, Battelle, Pacific Northwest USA 99352, USA 12-14 13th Pharmaceutical Technology Conference Strasbourg, Professor Mike Rubinstein, 13th Pharmaceutical France6N Analyst, January 1994, Vol.11 9 Date Conference Location Contact 17-19 International Symposium on Volatile Organic Montreal, Compounds (VOCs) in the Environment Quebec, Canada 18-22 6th International Conference on Near Infrared Lome, Spectroscopy Australia 19-22 ANALYTICA'94: 14th International Munich, Conference on Biochemical and Instrumental Analysis Germany May 7-12 8-12 8-13 8-13 9-13 16-19 1620 24-27 24-27 29-116 30-216 30-116 Food Structure Annual Meeting Toronto, Ontario, Canada Atlanta, GA, USA 85th AOCS Annual Meeting & Expo HPLC '94, Eighteenth International Minneapolis, MN , Chromatography USA CLEO '94: Conference on Lasers and Electro- Anaheim, CA, Symposium on Column Liquid Optics Focus 9 T h e Annual National Meeting and Exhibition of the Association of Clinical Biochemists 24th Annual Symposium on Environmental Analytical Chemistry 24th International IAEAC Symposium on Environmental Analytical Chemistry 3rd Symposium on Molecular Chirality International Symposium on Metals and Genetics: Toxic Metal Compounds in USA Brighton, UK Ottawa, Canada Ottawa, Ontario, Canada Kyoto, Japan Toronto, Ontario, Canada Environment and Life 5; Interrelation between Chemistry and Biology 42nd ASMS Conference on Mass Spectroscopy Chicago, IL, USA 14th Nordic Atomic Spectroscopy and Trace Naantali, Analysis Conference Finland Scandinavian Symposium on Infrared and Bergen, Raman Spectroscopy Norway Symposium Chairman, Dr.Wuncheng Wang, US Geological Survey, WRD, P.O. Box 1230, Iowa City, IA 52244, USA. Tel: +1319 337 4191, Fax: +1 319 354 0510; or Co-Chairmen, Dr. Jerald Schnoor, University of Iowa, Department of Civil and Environmental Engineering, Iowa City, IA 52242, USA. Tel: +1319 335 5649, Fax: +1319 335 5777; and Dr. Jon Dbi, Roy F. Weston, Inc., 1 Weston Way, West Chester, PA 19380, USA Tel: +1 215 524 6167. Fax: +1 215 524 6175 NIR-94, Peter Flinn, Pastoral and Veterinary Institute, Mt. Napier Road, Private Bag 105, Hamilton, Victoria 3300, Australia Tel: +61 55 730915.Fax: +61 55 711523 Miinchener Messe- und Ausstellungsgesellschaft mbH, Analytica '94Werbung Postfach 12 10 09, D-8000 Miinchen 12, Germany Tel: +49 89 51 07 143. Fax: +49 89 51 07 177 Dr. Om Johari,, SMI, Chicago (AMF O'Hare), IL Tel: + 1 708 529 6677. Fax: + 1 708 980 6698 AOCS EducatiodMeetings Department, P.O. Box 3489, Champaign, IL 61826-3489, USA Tel: +1217 359 2344. Fax: +1217 351 8091 Ms. J. E. Cunningham, Barr Enterprises, P.O. Box 279, Walkersville, MD 21793, USA Tel: +1 301 898 3772. Fax: +1 301 898 5596 Meetings Department, Optical Society of America, 2010 Massachusetts Avenue, NW, Washington, DC Tel: +l 202 223 9034. Fax: +1 202 416 6100 Focus 94, P.O. Box 227, Buckingham, Buckinghamshire, UK MK18 5PN Tel: +44 2806 613. Fax: +44 2806 487 Dr.M. Malaiyandi, CAEC, Chemistry Department, Carleton University, 1255 Colonel By Drive, Ottawa, Canada K1S 5B6 Tel: + 1 613 788 3841. Fax: + 1 613 788 3749 Dr. James F. Lawrence, Food Additives and Contaminants, Health and Welfare, Tunney's Pasture, Ottawa, Ontario, Canada K1A OL2 Professor Terumichi Nakagawa, Symposium on Molecular Chirality (SMC), Faculty of Pharmaceutical Sciences, Kyoto University, Yoshida-Shimoadachi-cho, Sakyo-ku, 606 Japan Fax: +8148 471 0310 (Professor Hara) Professor B. Sarkar, Department of Biochemistry, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G 1x8 60666-0507, USA 20036-1023, USA ASMS, 815 Don Gaspar, Santa Fe, NM 87501, USA Tel: +1 505 989 4517. Ari Ivaska, Abo Akademi University, Laboratory of Analytical Chemistry, Biskopsgatan 8, SF-20500 Abo Turku, Finland Dr.Alfred Christy, Department of Chemistry, University of Bergen, N-5007 Bergen, NorwayAnalyst, January 1994, Vol. 119 7N Date June 1-3 1-3 5-7 5-7 5-1 1 6-8 8-1 1 12-15 15-17 15-18 16-17 16-17 19-24 27-117 Conference Location Contact Second International Symposium on Hormone and Veterinary Drug Residue Analysis Biosensors 94-The Third World Congress on Biosensors VIth International Symposium on Luminescence Spectrometry in Biomedical Analysis-Detection Techniques and Applications in Chromatography and Capillary Electrophoresis VIth International Symposium on Luminescence Spectrometry in Biomedical Analysis-Detection Techniques and Applications in Chromatography and Capillary Electrophoresis 24th ACHEMA Conference on Plasma Science 6th International Conference on Flow Analysis 1994 PREP Symposium and Exhibit 16th Symposium on Applied Surface Analysis (ASSD) The Second International Symposium on Speciation of Elements in Toxicology and Environmental and Biological Sciences 14th International Symposium on Environmental Pollution 18th International Conference on Analytical Chemistry and Applied Chromatography/ Spectroscopy 20th International Symposium on Chromatography Special FEBS Meeting on Biological Membranes Bruges, Belgium New Orleans, USA Bruges, Belgium Bruges, Belgium Frankfurt, Germany Santa Fe, NM, USA Toledo, Spain Washington, DC, USA Burlington, MA, USA h e n , Norway Toronto, Canada Toron to, Canada Bournemouth, UK Espoo, Suomi-Finland Professor C.Van Peteghem, Symposium Chairman, Faculty of Pharmaceutical Sciences, University of Ghent, Harelbekestraat 72, B-9000 Ghent, Belgium Tel: +32 9 221 89 51 (ext. 235). Fax: +32 9 220 52 43 Kay Russell, Conference Department, Elsevier Advanced Technology, Mayfield House, 256 Banbury Road, Oxford, UK OX2 7DH Tel: +44 (0) 865 512242. Fax: +44 (0) 865 310981 Professor Dr. Willy R. G. Baeyens, Symposium Chairman, University of Ghent, Pharmaceutical Institute, Department of Pharmaceutical Analysis, Laboratory of Drug Quality Control, Harelbekestraat 72, B-9000 Ghent, Belgium Tel: +32 9 221 89 51. Fax: +32 9 221 41 75 Professor Dr. WUy R. G. Baeyens, Symposium Chairman, University of Ghent, Pharmaceutical Institute, Dept. of Pharmaceutical Analysis, Lab.of Drug Quality Control, Harelbekestraat 72, B-9000 Ghent, Belgium Tel: +32 (0) 9 221 89 51. Fax: +32 (0) 9 221 41 75 Dechema, Theodor Heuss-Allee 25, P.O. Box 970146, D-W-6000 Frankfurt am Main 97, Germany A. Perratt, Los Alamos National Laboratory, Group X-10, MS D-406, P.O. Box 1663, Los Alamos, NM 87545, USA Professor M. ValdrceUDr. M. D. Luque de Castro, (Flow Analysis VI), Departamento de Quimica Analitica, Facultad de Ciencias, E-14004 Cordoba, Spain Tel: +34 57 218616. Fax: +34 57 218606 Ms. Janet Cunningham, SymposiumExhibit Manager, Barr Enterprises, P.O. Box 279, Walkersville, MD 21793, USA Tel: +1 301 898 3772. Fax: +1 301 898 5596 Joseph Geller, Geller Microanalytical, 1 Intercontiental Way, Peabody, MA 01960, USA Tel: + 1 508 535 5595. The Second International Symposium on Speciation of Elements in Toxicology and in Environmental and Biological Sciences, Yngvar Thomassen, National Institute of Occupational Health, P.O.Box 8149 DEP, N-0033 Oslo 1, Norway Dr. V. M. Bhatnagar, Alena Chemicals of Canada, P.O. Box 1779, Cornwall, Ontario, Canada K6H 5V7 Tel: +l 613 932 7702. Dr. V. M. Bhatnagar, Alena Chemicals of Canada, P.O. Box 1779, Cornwall, Ontario, Canada K6H 5V7 Tel: +1 613 932 7702. Mrs J. A. Challis, Chromatographic Society, Suite 4, Clarendon Chambers, 32 Clarendon Street, Nottingham, UK NG15JD Tel: +44 602 500596. Fax: +44 602 500614 Professor Timo Korhonen, Biochemical Society, European Federation of Biochemical Societies (FEBS) , Department of General Microbiology, University of Helsinki, Mannerheimintie 172, SF- 00300 Helsinki, Finland8N Analyst, January 1994, Vol.11 9 Date Conference Location Contact July 3-7 International Chemometrics Research Meeting Veldhoven (Eindhoven) , The Netherlands Mrs. Gerrie Westerlaken, Conference Organizing Bureau VNW, Postbus 1558,6501 BN Nijmegen, The Netherlands Tel: +3180 234471. Fax: +31 80 601159 B. Jouffey, SFME 67, rue Maurice Gunsbourg, 94205, Ivry sur Seine cedex, France Tel: +33 1 46702844. Fax: +33 1 46708846 Dr. Steve Hill, Department of Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, Devon, UK PL4 8AA 18-22 XI11 International Congress on Electron Paris, Microscopy France 20-22 Seventh Biennial National Atomic Hull, Spectroscopy Symposium UK August The Second Changchun International Symposium on Analytical Chemistry(C1SAC) Changchun, China Professor Quinhan Jin, Department of Chemistry, Jilin University, Changchun 130023, China Tel: +8643182233 (ext.2433). Fax: +86431823907 Meetings Department, Optical Society of America, 2010 Massachusetts Avenue, NW, Washington, DC Tel: +1202 223 9034. Fax: +1 202 416 6100 ISBP Secretariat, Conference Office, McGill University, 550 Sherbrooke St. West, West Tower, Suite 490, Montreal, Quebec, Canada H3A 1R9 Tel: +1 514 398 3770. Fax: +1 514 398 4854 Mr. B. R. Hodson, American Chemical Society, 1155-16th Street N.W., Washington, DC 20036, USA Hungarian Chemical Society, H-1027 Budapest , Hungary Tel: +36 1201 6883. Fax: +36 1 15 61215 20036- 1023, USA 2-6 8-12 14-18 21-26 29-219 IGARSS '94: 1994 International Geoscience and Remote Sensing Symposium Pasadena, CA, USA International Symposium on Bacterial Polyhydroxyalkanotes (ISBP '94) Montreal, Quebec, Canada 208th ACS National Meeting (with Sessions of Analytical Chemistry, Environmental Chemistry, Chemical Health and Safety, etc ) 13th International Mass Spectrometry Conference Washington, DC, USA Budapest, Hungary September First International Symposium on Neuroelectrochemistry Coimbra, Portugal Profa.Dra. Ana Maria Oliveira Brett, Departamento de Quimica, Universidade de Coimbra, 3049 Coimbra, Portugal Tel: +351 39 22826. Fax: +351 39 27703 Dechema, P.O. Box 970146, D-W-6000 Frankfurt am Main 97, Germany GDCh-Geschaftsstelle, Abt. Tagungen, Varrentrappestr. 40-42, Postfach 90 04 40, D-6000 Frankfurt am Main 90, Germany Tel: +49 69 79 17 358.Fax: +49 69 79 17 475 SCI Conference Office, 14/15 Belgrave Square, London, UK SWlX 8PS Tel: +44 71 235 3681. Fax: +44 71 823 1698 Helios Rybicka, Faculty of Geology, Geophysics and Environmental Protection, University of Mining and Metallurgy, Al. Mickiewicza 30, PL-30-059 Krakow , Poland Tel: +48 12 333290. Fax: +48 12 332936 Marilyn Schwartz, Department of Pharmaceutical Chemistry, University of California, San Francisco, D. L. Miles, Analytical Geochemistry Group, British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, UK NG12 5GG Tel: +44 602 363100. Fax: +44 602 363200 Dr. A. M. Gil, Department of Chemistry, University of Aveiro, 3800 Aveiro, Portugal CA 9413-0446, USA 5-6 5-9 11-16 12-15 12-15 13-18 18-22 19-21 7th International Symposium on Synthetic Membranes in Science and Industry EUCMOS XXII: XXIInd European Congress on Molecular Spectroscopy Tubingen, Germany Essen , Germany Separations for Biotechnology Reading, UK 3rd International Symposium on Environmental Geochemistry Krakow, Poland 3rd International Symposium on Mass Spectrometry in the Health and Life Sciences San Francisco, CA, USA Ambleside, UK Geoanalysis 94: An International Symposium on the Analysis of Geological and Environmental Materials The Second International Conference on Applications of Magnetic Resonance in Food Science Aveiro, PortugalAnalyst, January 1994, Vol. 11 9 9N Date 19-23 21-23 21-23 22-24 25-28 26-30 Conference Locat ion XIIIth International Symposium on Medicinal Paris, Chemistry France 7th International Symposium on Bournemouth, Environmental Radiochemical Analysis UK 5th International Symposium on Stockholm, Pharmaceutical and Biomedical Analysis Sweden 12th National Conference on Analytical Chemistry Romania Constan ta, 5th International Symposium on Chiral Discrimination Sweden Stockholm, 16th International Symposium on Capillary Chromatography Italy Riva del Garda, October 2-7 29th Annual Meeting of the Federation of Analytical Chemistry and Spectroscopy Societies PREP '94: 11th International Symposium on Preparative and Industrial Chromatography 3-6 17-19 3rd International Symposium on Supercritical Fluids 3 0 4 1 1 OF'TCON '94 St.Louis, MO, USA Baden-Baden , Germany S trasbourg , France Boston, MA, USA November 6-12 Third Rio Symposium on Atomic Spectrometry Caracas, Venezuela 9-1 1 11th Montreux Symposium on Liquid Montreux, Chromatography-Mass Spectrometry (LC/ Switzerland MS; SFCMS; CEMS; MSMS) 10-1 1 17th International Conference on Chemistry, New Delhi, Bio Sciences, and Environmental Pollution India 18-22 Joint Oil Analysis Program International Pensacola, FL, Condition Monitoring Conference USA Contact CONVERGENCES/ISMC '94,120 avenue Gambetta, 75020 Paris, France Fax: +33 1 40 31 0165 Dr.P. Warwick, Department of Chemistry, Loughborough University of Technology, Loughborough, Leicestershire, UK LE11 3TU Tel: +44 509 222585 or +44 509 222545. Fax: +44 509 233163 Swedish Academy of Pharmaceutical Sciences, P. 0. Box 1136, S-111 81 Stockholm, Sweden Tel: +46 8 245085.Fax: +46 8 205511 Dr. G.-L. Radu, Romanian Society of Analytical Chemistry 13 Bul. Carol I, Sector 3,70346 Bucharest, Romania Swedish Academy of Pharmaceutical Sciences, P. 0. Box 1136, S-111 81 Stockholm, Sweden Tel: +46 8 245085. Fax: +46 8 205511 Professor Dr. P. Sandra, I. 0 .P.M.S., Kennedypark 20, B-8500 Kortrijk, Belgium Tel: +32 56 204960. Fax: +32 56 204859 FACSS, P.O. Box 278, Manhattan, KS 66502-0003, USA Tel: + 1 301 846 4797. GDCh-Geschiiftsstelle, Abt. Tagungen, Varrentrappestr. 4042, Postfach 90 04 40, D-6000 Frankfurt am Main 90, Germany Tel: +49 69 79 17 358. Fax: +49 69 79 17 475 Congres 'Fluides Supercritiques' Mle Brionne, ENSIC B.P. 451-1, rue Grandville, F-54001 Nancy Cedex, France Tel: +33 83 17 50 03. Fax: +33 83 35 08 11 Meetings Department, Optical Society of America, 2010 Massachusetts Avenue, NW, Washington, DC Tel: +1 202 223 9034. Fax: +1 202 416 6100 20036-1023, USA Professor Jos4 Alvarado, Universidad Simon Bolivar, Departamento de Quimica, Laboratorio de Absorcion Atomica, Apartado postal No. 89000, Caracas, 1080-A, Venezuela Fax: +58 2 938322/5719134/5763355/9621695 M. Frei-Hausler, Postfach 46, CH-4123 Allschwil2, Switzerland Tel: +41 61 4812789. Fax: +41 61 4820805 Dr. V. M. Bhatnagar, Alena Chemicals of Canada, P.O. Box 1779, Cornwall, Ontario, Canada K6H 5V7 Tel: +1 613 932 7702. Technical Support Center, Joint Oil Analysis Program, Bldg. 780, Naval Air Station, Pensacola, FL 32508, USA Tel: +1 904 452 3191. Entries in the above listing are included at the discretion of the Editor and are free of charge. If you wish to publicize a forthcoming meeting please send full details to: The Analyst Editorial Office, Thomas Graham House, Science Park, Milton Road, Cambridge, UK CB4 4WF. Tel: +44 (0)223 420066. Fax: +44 (0)223 420247.

ISSN:0003-2654    

DOI:10.1039/AN994190005N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Analyst, January 1994, Vol. 119 9 European Standardization: Guidance on the Assessment of Occupational Exposure to Chemical Agents* R. Grosjeant Ministerie van Tewerkstelling en Arbeid, Laboratorium voor Industriele Toxicologie, Belliardstraat 51, B-1040 Brussels, Belgium Working group 1 of CEN TC 137 has produced a draft proposal for the assessment of exposure to chemical agents and measurement strategy. A review of the standard is given. The purpose is to give practical guidance to those who have to carry out these assessments. A systematic approach allows the number of measurements to be reduced. The report of the work done allows communication in an efficient way with interested parties: workers, occupational physicians and the labour inspectorate. Keywords: Occupational chemical exposure assessment; European standardization; CEN guidelines Introduction The use of limit values is an important tool for the protection of the health of workers exposed to chemical agents.Several national and international bodies propose occupational ex- posure limits. At EEC level, two different types of limit values exist: binding limit values for asbestos, lead and vinyl chloride; and ‘indicative limit values’ for 27 substances so far. The European Commission intends to publish more limit values. Directives that may be adopted by the Council of Ministers or by the Commission, depending on the procedure, have to be translated by Member States into their legislation. Legisla- tion regarding health and safety at work at European Community level is based on Article 118A of the Treaty.This means that these rules have to be considered as minimum requirements. Member States may adopt stricter regulations, which in terms of limit values mean that they may promulgate lower limit values. In principle, the described procedure can be used for any type of limit value. It is not practical to provide every worker with measuring equipment permanently in order to be able to guarantee that his or her exposure does not exceed the limit values. By using some formalized approaches and techniques, it is possible to reduce the measuring effort drastically. In many instances it is even not necessary to rely on measurements. Basic requirements for such formalized approaches can be found in legislation, e.g., Directive 88/642/EEC amending Directive 80/1107/EEC.Directive 80/1107/EEC contains basic preventive measures to reduce workers’ exposure to chemical, physical and biological agents. Directive 88/642/EEC intro- duces the two different types of limit values and the principle of the formal assessment of exposure. On 17 May, 1993, the European Commission made a proposal for a Council Directive on the protection on health and safety of workers from the risks related to chemical agents at work. If adopted, this Directive will become an individual * Presented at the Conference on Modern Principles of Workplace Air Monitoring: Pumped and Diffusive Sampling for Contaminants, Geilo, Norway, February 15-18, 1993. + Convenor of CEN TC 137 working group 1. Directive under the framework Directive 89/391/EEC, and Directives 80/1107/EEC and 88/642/EEC will be repealed.In some countries some legislation, guidelines or standards already exist on this subject, e.g., in the UK, Germany and Belgium. Working group (WG) 1 of CEN TC 137 started its activities in November 1988. In May 1991 it was able to present a draft proposal to the Technical Committee. The document was circulated as a prEN standard for voting in the CEN Member States from March to September 1992. In December 1992 a meeting took place in Antwerp to discuss the comments received during the circulation of the draft proposal. The formal vote will probably take place in 1994. At the beginning of the activities of WG 1 it appeared that it was very difficult to find a direction that could meet the different expectations of the experts from different countries.However, at each meeting mutual understanding between the experts increased and this has resulted in a document that gives practical guidance to those who have to carry out assessments of exposure on the workfloor. The standard contains a number of informative annexes. It is stressed that the standard deals only with exposure by inhalation. A global health risk assessment has to take into account all exposure routes. Procedure The procedure includes two phases: (1) An occupational exposure assessment (OEA): at the start of the procedure the exposure is compared with the limit value. The OAE has to be repeated when a new limit value is proposed or when a relevant change in exposure conditions occurs.(2) Periodic measurements (PM): to check regularly if exposure conditions have changed. Terminology and Definitions A number of definitions are given. Some of them are the same definitions as those in Directive 88/642/EEC. No attempt is made to define ‘compliance’ as this is a matter for legislation. The topic of definitions is often controversial; the question is how far one should go in trying to define some terms without becoming too trivial. At the level of the Technical Committee it was decided that a working group with Mr. J. C. Guichard (INERIS, France) as the convenor should look at the definitions of the various working groups in order to avoid contradictions. There was a consensus that the different working groups would not be forced to adopt definitions that they do not like or do not need.10 Analyst, January 1994, Vol.11 9 Occupational Exposure Assessment (OEA) The occupational exposure assessment consists of three steps. First, potential exposures are identified. An inventory of all products and chemicals in the workplace is made and information on these substances is collected (physico-chemical properties, health hazards, limit values, etc.). In many countries such an inventory should already be available in order to comply with regulations on chemical hazards, medical surveillance, etc. Second, the work processes and procedures in which the chemical agents are involved are studied. Third, the combination of these two steps allows an assessment of the exposure to be made. A structured approach is required in this process, which may be conducted in three stages: an initial appraisal, a basic survey and a detailed survey. Identify potential exposure (see section 4.1) Determine workplace factors (see section 4.2) I Initial appraisal of exposure (see section 4.3.1) t e Yes Exposure unlikely ? (see section 4.3.1) I V No I V I Conduct basic survey (see section 4.3.2) I I I-- Yes- Exposure acceptable ? - No - (see section 4.6.2) I V Uncertain I V Conduct detailed survey (see section 4.3.3) 1 I V I V I V I V Yes I V Exposure acceptable ? No - Yes + No f- Periodic measurements necessary ? - Establish scheme for periodic measurements (see chapter 5) I Perform periodic measurements I f I V I I-remec Exposure acceptable ? - No --+ Yes IeDort (see ChaDter 6) 1 ;action1 I 1 I I V I Repeat assessment1 Fig.1 Schematic overview of procedure Data about the temporal and spatial distributions of the concentrations of the substances in the workplace have to be collected. The procedure that is proposed does not require that every stage of the assessment is used. If it is expected that the exposure exceeds the limit value or if it is clearly determined that exposure is well below the limit value, then the occupational exposure assessment can be concluded and appropriate action taken. Initial Appraisal In this stage, the list of chemicals and the workplace factors yield a consideration of the likelihood of exposure. Variables that affect personal exposure have to be looked at. These variables are influenced by the emission sources, the disper- sion of air pollutants, the actions and behaviour of the individuals.If this initial appraisal shows that the presence of an agent in the air at the workplace cannot be ruled out for certain, it needs further consideration. Basic Survey The basic survey provides quantitative information about exposure of workers with particular account of tasks with high exposure. Possible sources of information are earlier measure- ments, measurements from comparable work processes and reliable calculations based on relevant quantitative data. When calculations are used, care should be taken not to overlook aspects that are difficult to quantify: concentration gradients, diffusive emissions from spills, waste tins, contami- nated clothing, etc. If the information obtained is insufficient to enable a valid comparison to be made with the limit values, it must be supplemented by workplace measurements.Detailed Survey The detailed survey is aimed at providing validated and reliable information on exposure when it is close to the limit value. Measurement Strategy Bearing in mind that measurements are expensive, it is important to take an approach that permits the most efficient use of resources. This means that it should be possible to stop the procedure in an early stage by using techniques that are easily applied and that may be less accurate. Other possibili- ties may be worst case measurements, sampling near emission sources or screening measurements. The requirements and measuring ranges for these different measurement tasks should be defined in such a way that they allow the occupational exposure assessment to be completed without further investigation.In other instances, where exposures are suspected to be close to the limit value, it will be necessary to undertake a more accurate investigation, making full use of the capabilities of instrumental and analytical techniques. Selection of Workers for Exposure Measurements Some general guidelines are given for selection of workers for exposure measurements. If workers are sampled purely on an at random basis large number of samples are needed. Some techniques such as sub-dividing the exposed population into homogeneous groups, critical examination of the work-pattern, examination of preliminary measurement results allow the sampling effort to be reduced considerably compared with sampling on a ‘blind’ purely statistical basis.Analyst, January 1994, Vol.119 11 Representative Measurements Measurement conditions shall be selected in such a way that measurement results give a representative view of exposure under working conditions. This means that personal sampling should be carried out for an entire working period, or a time period that is representative of it. Fixed-point measurements may be used when they allow personal exposure to be assessed. In some instances no personal measuring or sampling device is available. Measurements should be carried out on sufficient days and during specific operations. It is important to consider different episodes during which exposure conditions may vary (night and day cycles, seasonal variations).Care should be taken to avoid auto-correlation between different measurement results. This implies that measurements should be spread over a sufficient time period. Worst Case Measurements When it is possible to identify clearly episodes where higher exposures occur, e.g., a high emission due to certain working activities, one can select sampling periods containing these episodes. Sampling efforts can be concentrated on these periods with relatively unfavourable conditions. If the concen- trations measured this way are presumed to apply for the whole of the working period, a safety factor will be built in. Measurement Pattern A number of practical issues play an important role in the pattern of sampling: frequency and duration of a particular task, optimum use of occupational hygiene and analytical resources. Representativeness of the data for the identified tasks and periods is essential. In many workplaces work is varied throughout the working period, which itself may be interrupted.The duration of an individual sampling is often dictated by constraints of the method of sampling and analysis in practice, e.g., the time needed to collect a sufficient amount of analyte. Unsampled time remains a serious weakness in the cred- ibility of any exposure measurement. During this time careful observation is always necessary. The assumption that changes have not occurred in the unsampled period must always be critically examined. Annexe 1 of the draft standard contains a table that can be used as a guide for the minimum number of samples to take as a function of sampling duration in the case of a homogeneous working period.The table is a combination of practical experience and statistical arguments. Measurement Procedure The measurement procedure should give results representa- tive of worker exposure. The management procedure contains the agents, the procedure for sampling and analysis, the sampling locations(s), the jobs to be monitored, the duration of sampling, the timing and duration between measurements and technical instructions concerning the measurements. Annexe 2 of the draft standard contains examples of calculations of the occupational exposure concentrations from individual analytical values. The occupational exposure con- centration is the arithmetic mean of the measurements in the same shift with respect to the appropriate reference period of the limit value of the agent under consideration.WG 2 has already proposed general requirements for measurement procedures .2 Conclusion of the Occupational Exposure Assessment The prescribed procedure has to come to a conclusion. No unique formal scheme is proposed in the standard. Annexes 3 and 4 of the draft standard give examples of formal schemes that might be used. Other countries may propose others. In Belgium a scheme proposed by Tuggle based on one-sided tolerance limits has been used.3.4 Whatever scheme is used, one of three conclusions should be determined. (1) The exposure is above the limit value: the reasons for the overexposure should be determined and remedial action taken.The occupational exposure assessment should be repeated. (2) The exposure is well below the limit value and is likely to remain so on a long-term basis owing to the stability of conditions at the workplace and the arrangement of the work process. In this case periodic measurements are not needed. However, it must be regularly checked whether the occupa- tional exposure assessment leading to that conclusion is still applicable. (3) The exposure does not fit into categories 1 or 2. Although the exposure may be below the limit value, periodic measurements are still required. In certain cases, the periodic measurements can be omitted, depending on the properties of the agents on the workprocess. Technical guidelines can provide criteria for deciding whether or not to carry out periodic measurements.Annexe 5 of the draft proposal gives an example of a procedure for considering if and when periodic measurements are required. The purpose of the periodic measurement is to check the validity of the occupational exposure assessment and to recognize changes of exposure with time. The occupational exposure assessment is only concluded when a report has been made of the results of the assessment and a record of any remedial action deemed necessary. Periodic Measurements (PM) The emphasis of periodic measurements is on longer term objectives such as checking that control measures remain effective. Information is likely to be obtained on trends or changes in pattern of exposure so that action can be taken before excessive exposures occur. For the results of a periodic sampling programme to be of real use, it must be possible to compare consecutive sets of results.This implies that the methodology used for collecting the samples needs to be rigorously planned to ensure that the over-all error can be estimated and that genuine change in the exposure pattern can be recognized. The interval between measurements has to be established after consideration of a number of factors such as the process cycles, closeness to the limit value and the temporal variability of the results. Together with other considerations, this may lead to intervals between periodic measurements varying from less than 1 week to more than 1 year. Annexe 6 of the draft proposal gives an example of a scheme for determining intervals between periodic measurements.Reporting Reports have to be written of the occupational exposure assessment and of any periodic measurement. Each report should give reasons for the procedures adopted in the particular workplace. The content of the report is described. It is clear that such a report is very valuable for the labour inspectorate, for the workers who should have information on their exposure and for the occupational physician.12 Analyst, January 1994, Vol. I I9 Handling of Data It is evident that an important amount of data will be generated during the OEAs and the PMs. In order to prevent accumulation of a large number of unused data and in order to obtain a high return from the time and effort invested, it is necessary to use appropriate statistical techniques. Annexe 7 of the draft proposal gives two examples of statistical analysis of data: the moving weight average and the probability plot.The data can be useful for epidemiological studies and the evaluation of occupational exposure limits. Automated Measuring Systems During the discussions of WG 1, some participants felt it was necessary to deal with automated measuring systems. Such measuring systems are used in vinyl chloride production and polymerization plants, sterilization processes with ethylene oxide, etc. It proved to be difficult to insert this concept into the working document in preparation without lengthy discus- sions that would cause further delay. A joint working group was set up with CENELEC to deal with direct-reading instruments.Discussion and Conclusions The draft standard prEN 689 on monitoring strategy is clearly a compromise between different approaches. Experts from industry or from government bodies from different countries come to such a working group with the conviction that their own approach is the right one. In general, the willingness to adopt new or different approaches is very low. Exposure measurements are not a common practice yet in many countries of the EEC. Even in countries were legal requirements on exposure monitoring exist, the application of these requirements is not general, especially in small and medium undertakings. In Belgium, for instance, there is an extensive system of medical surveillance of workers with strict tariffs that is applicable for every employer, even with only one employee.The costs of medical surveillance do not cover air monitoring. Some employers consider measurements only as an extra cost, in addition to medical surveillance. There needs to be a change in the perception of workers’ health protection from secondary to primary prevention. This will certainly take some time. A system to help the small and medium undertakings to carry out assessments of exposures will certainly improve the widespread application of this kind of procedure. The prescribed procedures often tend to minimize the number of measurements by focusing on high exposures and compare these with limit values. It is clear that this kind of ‘compliance monitoring’ will not give a complete or correct picture of the exposure situation in a certain industry.In the end, there is a conflict between the process of gathering exposure data and the will to reduce exposures to a level at which exposure measurements are no longer relevant from the standpoint of preventing health effects. A healthy workplace is a workplace where measurements are no longer needed! Fortunately (or unfortunately, depending on the position) there will be sufficient opportunities to assess and often measure exposures in future years in Europe. Questions such as how to deal with exposures to more than one substance and the minimum sampling frequency in a periodic measurement programme do not receive a clear answer in the standard. It was accepted that these matters have to be dealt with in legislation, which normally is adopted only after consultation between employers’ and employees’ representatives and takes into account economic and social factors. In the process of standardization, no such formal consultation takes place. Standardization cannot be used as a kind of back-door entry to give solutions to problems that are not solved elsewhere. References 1 Workplace A tmospheres-Guidance for the Assessment of Exposure to Chemical Agents for Comparison with Limit Values and Measurement Strategy, prEN 689, March 1992, European Committee for Standardization, Brussels. 2 General Requirements for the Performance of Procedures for Workplace Measurements, prEN 402, Final draft October 1993, European Committee for Standardization, Brussels. Workplace Atmospheres-Monitoring Strategy, NBN T 96-002 (only in Dutch and French), Institut Belge de Normalisation IBN, Brussels, 1987. 4 Tuggle, R. M., Am. Znd. Hyg. Assoc. J . , 1982, 43, 338. 3 Paper 310321 I F Received June 4, 1993 Accepted July 12, 1993

ISSN:0003-2654    

DOI:10.1039/AN9941900009

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

10N Analyst, January 1994, Vol. I I9 Conference Reports EIRELEC ‘93-Electrochemistry to the Year 2000, Dunraven Arms Hotel, Adare, Co. Limerick, Ireland, September 11-15, 1993 particles, was then discussed by Dr. Fernando Silva. This closed the section on electrochemical methodology. The session on electrochemical sensors began with Profes- sor Joseph Wang who took the audience on a guided tour of sensing technology relevant to environmental and medical applications. A battery-operated sensor for lead showed the proximity of this technology to the market-place. The theme continued with Professor Gordon Wallace, who described how conducting electroactive polymers could be used in the development of sensing systems to investigate the determination of various species such as phosphate and nitrate ions, proteins and chloramines.L to R: Professor Alan Bard, Professor David Williams and Craig Marvin The conference was held in the beautiful surroundings of Adare village, close to Limerick, in the south-west of Ireland. The subject matter was very broad and was split into three main sections: electrochemical methodology, sensors and technology. The underlying theme of the meeting was ‘Electrochemistry to the Year 2000’. Each speaker was asked to give their views on which direction electrochemistry should be taking with the approach of the 21st century. Dr. Dermot Diamond initiated the meeting with some traditional Irish fiddle music before the conference began in earnest. Dr. Allen Bard opened the methodology section with a very detailed breakdown of the scanning electrochemical microscope, which uses piezoelectric technology originally meant for scanning tunnelling microscopy (STM), in the study of reaction kinetics and the probing of electrode films.Dr. Sheelagh Campbell then discussed the use of STM to image biological molecules including DNA, and specific retrovirus molecules such as HIV-1. Next, professor Andrew Hamnett showed how the constructive combination of ellipsometry and Fourier transform infrared spectrometry (FTIR) could be used to gain information on the mechanism of film formation and their subsequent behaviour. Dr. Maher Kalaji followed by presenting some preliminary data using SNIFTIRS to investigate structural changes during the redox switching of poly(ani1ine). Molecular modelling images were then used to rationalize the observed effects.The first evening’s entertainment took the form of a mixer, which is to say that both Murphy’s and Jameson’s Irish whiskey were mixed in large quantities by the delegates. Day two began with Dr. David Williams’ talk on electro- chemical imaging of electrode/electrolyte surfaces by means of the scanning laser microscope. Images obtained are a function of the electrode, and not of its topography or composition. Dermot Diamond showed how the use of sensor arrays in flow injection can greatly increase the precision and accuracy of experimental data compared with single electrodes. Refer- ence was made to the sensing of potassium and ammonium ions by neutral ionophores. The use of anodic stripping voltammetry in the determina- tion of metal ions at trace levels, in the presence of suspended L to R: Dr.Robert O’Neill, Dr. Dermot Diamond and Professor Joseph Wang enjoying the free Jamesons and Murphys in the Hotel bar The last presentation of the second day saw Dr. Robert O’Neill present results for the investigation of brain extracel- Mar uric acid detected using in vivo probes. The concentra- tion was shown to be related to the size of probe used. On the second evening most delegates attended the Irish gala night whereupon they were treated to the delights of traditional harp playing as an accompaniment to the magnificent Irish cuisine. This was followed by an impromptu guest appearance, in the bar of course, by Gordon Wallace who showed that not all Australians sing as badly as Jason Donovan and look like Rolf H a n i s - o r do they? The third day opened with Professor Phil Bartlett’s talk entitled ‘Enzymes, Electrons, and Electrodes 11-Biology Bites Back’.This discussion dealt with the problems associated with the incorporation of biological molecules into sensor structures. Next, a novel amperometric transducer for biosensor design, based on the IiquidAiquid interface, was presented by Dr. Hubert Girault. The enzymic reactions of urease and11N Analyst, January 1994, Vol. 11 9 ~ ~~ Professor Gordon Wallace (or is it Rolf Harris) providing the entertainment towards the end of the evening butyrylcholinesterase were studied using assisted-ion and ion transfer reactions, respectively, as the mode of sensing.The subject of electrochemical technology was first dis- cussed by the sage, Dr. David Schiffrin. In his talk, he gave a cartoon-assisted overview of potential applications for the combination of optical methods with electrochemistry, the emphasis being on the development of new types of sensors constructed by silicon etching techniques. This rounded off day three of the conference which was followed by an excursion into the Irish countryside. Some of those already much the worse for wear found the Irish roads a bit too bumpy for comfort. The final day of the meeting continued the theme of electrochemical technology. Dr. John Bockris spoke on ‘The Electrochemistry of Cleaner Environments’ in which he described the application of electrochemistry to such diverse problems as the disposal of human waste on the Space Shuttle and the removal of iron staining from soil in Silicon Valley in the USA.Dr. Frank Walsh then discussed the design of reactors for electrochemical synthesis and treatment of environmental wastes. Closing the session, and the meeting, Dr. Mike Lyons dealt with the subject of electrocatalysis using polymer-modified electrodes incorporating catalytic microparticles and electron transfer mediators. At the end of the four days, and from the various discussion sessions, the general opinion was that electrochemistry will play an increasingly prominent role in the advancement of technology towards the year 2000 and beyond. The authors look forward to Eirelec ’95, at the same venue, to see what progress has been made.P. D. Beattie M. D. Osborne International Symposium on Electroanalysis in Biomedical, Environmental and Industrial Sciences, April 20-23,1993, Loughborough, Leicestershire, UK Dr. Arnold Fogg and Loughborough University of Technol- ogy again extended their hospitality and hosted the biannual conference on electroanalysis. A packed scientific and social programme awaited our morning arrival in Loughborough on Tuesday. In addition, the sports facilities were made available to those who could find time in their schedule. The varied scientific programme of 35 lectures and 35 posters included keynote lectures on: advanced electroana- lytical techniques versus AAS, ICP-AES, ICP-MS in environ- mental analysis (Dr. P. M. Bersier, Riehen, Switzerland), catalytic cathodic stripping voltammetry of elements in sea-water (Dr. C.M. G. van den Berg, Liverpool, UK), environmental applications of ion chromatography with ISE detectors (Professor A. K. Covington, Newcastle, UK) and switching kinetics of electroactive polymers (S. Briickenstein, Buffalo, USA). Professor J. D. R. Thomas (Cardiff, UK) gave an extensive tour of his work over many years in the field of ion-selective electrodes. Electrodes which utilize liquid ion exchangers, acrylic pol yether and crown ether type electrodes were briefly discussed before moving along to talk of electrodes in which the membranes are fabricated by enzyme immobilization on nylon. Professor Thomas closed by describ- ing the modelling of these electrodes in a flow system for the detection of enzyme inhibitors, which he hopes to adapt to determine pesticide residues.Along the theme of immobilized enzymes, Professor P. N. Bartlett (Southampton, UK) gave an introduction to the uses of electropolymerization, entrapped enzymes and their kinetic studies. The use of electropolymerization with enzymes grown across narrow gaps has been applied to novel responsive switching devices. Glucose sensors were reported using both this method and more conventional electropolymerized poly- (phenol) films. Professor A. R. Hillman (Leicester, UK) discussed dynamic separation of mobile species transfer processes at polymer modified electrodes using the electro- chemical quartz crystal microbalance. In the final keynote lecture Professor M. R. Smyth (Dublin, Ireland) reviewed his recent work on microelectrode flow cells which have been used in LC-EC for the determination of salbutamol and terbutaline in plasma.This detector has been subsequently developed in conjunction with Luntes’ group (Kansas Univer- sity) for CE studies of microdialysis samples. Novel work on chemically, polymer and biologically modified electrodes was also reviewed before recent research results were discussed. Finally, three electrode systems were detailed: an osmium containing redox polymer modified carbon fibre microelec- trode , a poly(pyrro1e) modified microelectrode for anion detection in ion chromatography and lastly an enzyme bilayer polymeric microelectrode for glucose determination. In addition to the keynote lectures there were a wide12N Analyst, January 1994, Vol.119 variety of other interesting contributions to the programme. Dr. B. G. D. Haggett (Luton, UK) told of the modelling of the mechanistic aspects of microbial whole cell biosensors. The micro-organisms were physically entrapped between a mem- brane and the working electrode. Dr. Haggett described work carried out using an Anotec membrane which gives a rapid response. The membrane has a cross-section capillary like structure with a high density of uniform pores, which the microbial cells are unable to penetrate. The modelling of these devices for environmental monitoring of herbicides and toxic metals was discussed. Dr. R. 0. Ansell (Glasgow, UK) described the manufacture of Pt microelectrodes and their application to the determination of oxygen, ascorbic acid and pharmaceutical products.Dr. E. J. Watt (Birkbeck, UK) described a novel microelectrode array detector which was used in conjunction with rapid scan palsed amperometric techniques to improve analysis in flowing solutions. Compari- son of dopamine detection obtained by rapid scan techniques with conventional detection techniques showed improved qualitative analysis. Dr. J. W. Paynter (Birkbeck, UK) showed us how to predict gas sensor responses using basic molecular parameters and multi-regression analysis. Anodic voltammetric determination of water in acetone at Pt micro- electrodes was presented by Dr. Z. Stojek (Warsaw, Poland). Dr. H. P. Bennett0 (Kings, UK) described how to minimize interference of endogenous electroactive compounds by placing a pre-oxidizing device before the biosensor in a flow line used for on-line monitoring of extracellular levels of glucose and glutamate in the brain. In addition to the well organized symposium dinner on Thursday evening, an extremely interesting trip to the nearby museum of science and industrial history at Coalville was laid on for those interested in the local mining history of Leicestershire. The museum, built on the site of a disused mine, housed exhibitions of local history as well as a science park for children (where most of the delegates were seen to spend a fair amount of time!). Probably the most interesting item the guide pointed out to us on our tour of the old mines was a ‘hotline’ in the control room installed by the Post Office in the provision of the event of a nuclear holocaust for rapid evacuation of the mine for safety reasons! In summary, an interesting and informative four days were well spent in Loughborough. Amiel Farrington, Birkbeck College, London, UK

ISSN:0003-2654    

DOI:10.1039/AN994190010N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

12N Analyst, January 1994, Vol. 119 Future Issues will lnclude- On-line Chromium Determination by Adsorptive Cathodic Stripping Voltammetry-Andrew M. Dobney and Gillian M. Greenway Development of a Disposable Amperometric Sensor Based on a Chemically Modified Screen-printed Carbon Electrode for Reduced Nicotinamide Adenine Dinucleotide-Steven D. Sprules, John P. Hart, Stephen A. Wring and Robin Pittson Development of Amperometric Sensors for Uric Acid Based on Chemically Modified Graphite-Epoxy Resin and Screen- printed Electrodes Containing Cobalt Phthalocyanine- Markas A. T. Gilmartin, John P. Hart and Brian J. Birch Functionalized Cyclodextrins as Potentiometric Sensors for Onium Ions-Paul S. Bates, Ritu Kataky and David Parker Hand-held Instrumentation for Environmental Monitoring- Claudius D’Silva and Gwyn Williams Selective Membrane Electrodes for Analysis-J.D. R. Thomas Organic-phase Application of an Amperometric Glucose Sensor-Emmanuel I. Iwuoha and Malcolm R. Smyth Mathematical Model of Toxicity Monitoring Sensors Incor- porating Microbial Whole Cells-Barry G. D. Haggett Determination of Nitrate in Carbon Black by Using a Nitrate-selective Electrode-Ricardo Perez-Olmos, JosC M. Merino, Izaskun Ortiz de Zarate, JosC L. F. C. Lima and Conceiqao B. S. M. Montenegro Batch and Flow Determination of Uranium(v1) by Adsorptive Stripping Voltammetry on Mercury-film Electrodes- Anastasios Economou, P. R. Fielden and A. J. Packham Horseradish Peroxidase Assay-Radical Inactivation or Sub- strate Inhibition? Revision of the Catalytic Sequence Follow- ing Mass Spectrum Evidence-Ramin Pirzad, Antony A.Dowman and David C. Cowell Ionophore-Ionomer Films on Glassy Carbon Electrodes for Accumulation Voltammetry. Investigation of a Lead(rr) Iono- phore-Damien W. M. Arrigan, Gyula Svehla, John Alder- man and William A. Lane Simple Solid Wire Microdisc Electrodes for the Determina- tion of Vitamin C in Fruit Juices-Amiel M. Farrington, Nidhi Jagota and Jonathan M. Slater Prediction of Gas Sensor Response Using Basic Molecular Parameters-Jonathan M. Slater and J. Paynter Ion-selective Field-effect Transistor and Chalcogenide Glass Ion-selective Electrode Systems for Biological Investigations and Industrial Applications-Yuri G. Vlasov, Eugene A. Bychkov and Andrey V. Bratov Amperometric Biosensor for Phenols Based on a Tyrosinase- Graphite-Epoxy Resin Biocomposite-Joseph Wang, Fang Lu and David Lopez Determination of Ultra-trace Amounts of Selenium(1v) by Flow Injection Hydride Generation Atomic Absorption Spec- trometry With On-line Preconcentration by Coprecipitation With Lanthanum Hydroxide-Elo Harald Hansen and Guanhong Tao Electrochemical Immobilization of Enzymes.Part VI. Micro- electrodes for the Detection of L-Lactate Based on Flavo- cytochrome 6 2 Immobilized in a Poly(pheno1) Film-Philip N. Bartlett and Daren J. Caruana Dynamic Separation of Mobile Species Transfer Processes at Polymer Modified Electrodes Using the Electrochemical Quartz Crystal Microbalance-A. Robert Hillman, Noelle A. Hughes and Stanley Bruckenstein Advanced Electroanalytical Techniques versus Atomic Absorption Spectrometry, Inductively Coupled Plasma Atomic Emission Spectrometry and Inductively Coupled Plasma Mass Spectrometry in Environmental Analysis- Pierre M. Bersier, Jonathon Howell and Craig Bruntlett

ISSN:0003-2654    

DOI:10.1039/AN994190012N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Analyst, January 1994, Vol. 119 13 Measurement of Coarse Aerosols in Workplaces* A Review James H. Vincent Division of Environmental and Occupational Health, School of Public Health, University of Minnesota, Box 807 Ma y o , 420 Delaware Street SE, Minneapolis, MN 55455, USA Coarse aerosol fractions in workplaces are sampled if it is felt that particles of all sizes may pose a risk to health. Although the so-called ‘total’ aerosol has been widely used to refer to the relevant coarse fraction, practical measurement has been very dependent on the actual sampling instrument used. This in turn has led to great uncertainty about what was being measured. In the 1980s’ the concept of inhalability was proposed, based on the aerosol particle size fraction that enters the human head through the nose and/or mouth during breathing.Now there is substantial agreement by most of the world’s major criteria-setting bodies on a quantitative definition taking the form of a single curve describing the probability of inhalation as a function of particle aerodynamic diameter. This definition now forms a truly health-related ‘yardstick’ against which to assess the performances of practical sampling devices. In turn, more and more countries are beginning to adopt the new criterion for health-related aerosol measurement in their standards, replacing the old ‘total’ aerosol concept. Experiments in wind tunnels to investigate the performances of previous samplers for ‘total’ aerosol show that most of them do not satisfactorily match the new inhalability criterion. A small number of samplers designed specifically for the inhalable fraction have been proposed and are available commercially.They include samplers for both static (or area) and personal sampling. Keywords: Coarse aerosols; workplace monitoring Introduction The routes of aerosol exposure may involve skin deposition, the food chain (after deposition on plants, etc.) and inhalation. Of these, the inhalation route is of great interest in occupational health, representing a major potential source of hazard for workers in many occupational environments. The nature and magnitude of the hazard in a given situation depend on a complex combination of many factors, including particle size distribution (which governs how the aerosol enters the body by inhalation, and how it penetrates into and is subsequently deposited in the respiratory tract), airborne concentration (which governs how much is deposited), and particle morphology, mineralogy and chemical composition (which govern the subsequent fate and biological responses to the presence of the particles in contact with vulnerable tissue).Ideally a standard should contain the following main components : (1) Criteria relating to the scientific basis upon which, for a given contaminant, a measurement or assessment procedure is * Presented at the Conference on Modern Principles of Workplace Air Monitoring: Pumped and Diffusive Sampling for Contaminants, Geilo, Norway, February 15-18, 1993. chosen. For aerosols, a fraction may be identified based on chemical composition and on particle size. (2) Measurement instrumentation, the technical means by which the relevant airborne contaminant, as identified in the specific criteria, can be quantified. This includes particle size-selective sampling instrumentation backed up by appropriate analytical methodology.(3) Sampling strategy, describing how such instrumentation is used in practice to assess the exposures of individuals (or groups of individuals). This involves considerations of where to sample, duration, frequency, etc., and should take account of the inter- and intra-individual variabilities in exposure. (4) A limit value, defining the upper end of the range of intensity or magnitude of permissible exposure to the fraction identified in the criterion for the substance in question.For airborne contaminants, it is usually described in terms of an airborne concentration (e.g., mass or number per unit volume of air), derived from a measurement made by sampling over an appropriate period of time. The usual underlying rationale is that this represents the ‘threshold’ level of exposure at, and below, which, according to current knowledge, there is no evidence of injury to workers if the substance is inhaled day after day. For many substances, a ‘full-shift’ 8 h time-weighted average (TWA) is appropriate; for others, a shorter reference period might be defined. In principle, a limit value should not be assigned until the other three components have been established. Some biologically active particles (e.g., bacteria, fungi, allergens) may, if they deposit in the extrathoracic airways of the head, lead to inflammation of sensitive membranes in that region, such as symptoms of ‘hay-fever’ (e.g., rhinitis).Other types of particle (e.g., nickel, radioactive material, wood dust) depositing in some parts of the same region may lead to more serious local conditions, such as ulceration or nasal cancer. Other types of particle may not produce such serious clinical effects, but may result in significant irritation and so constitute a ‘nuisance’. For all these, and for aerosol substances that are soluble and are known to be associated with systemic effects (where toxic material can enter the blood after deposition in any part of the respiratory tract and be transported to other organs), criteria for standards should be specified in terms of all that is inhaled.It is therefore clear that inhalable aerosol is a fraction which is an objective for measurement in itself in many occupational situations. This is the subject of this paper. Criteria for the Sampling of Coarse Aerosols In the past and, indeed, in most countries, the previous recommendations for the health-related sampling of coarse particles have been based on the concept of so-called ‘total’ aerosol. This concept is intended to relate to all particulate matter which might be considered airborne. However, most14 Analyst, January 1994, Vol. 119 practical sampling instruments for ‘total’ aerosol have been developed without particular regard to specific quantitative criteria or indices, and their performance characteristics have varied greatly from one to the other.Hence it follows that switching from one instrument to another in a given practical situation might well produce different measurements of exposure, even though the actual level of exposure itself might not actually have changed. With this in mind, the idea first emerged in the 1970s of the human head as an aerosol sampler and, hence, of inhalability as a quantitative definition of what had previously been known as ‘total’ aerosol. A number of important experimental studies were subse- quently conducted in laboratories in the UK and Germany to determine the efficiency with which particles enter the human head during breathing through the nose and/or mouth. These experiments, involving life-sized human mannequins in wind tunnels, provided data for a range of wind speeds relevant to workplace exposures and for particles with aerodynamic diameter up to 100 pm.1-4 All the sampling efficiency results were reported for head orientations with respect to the wind averaged uniformly over 360” about a vertical axis.It was found that this orientation-averaged efficiency of inhalation of a particle can, for most practical workplace purposes, be described in terms of a single function of particle aerodynamic diameter (dae), starting off at 100% for very small particles and falling to about 50% for particles with dae around 30 pm and above. Data from experiments such as these have formed the basis of recommendations for replacing the old ‘total’ aerosol concept with a quantitative sampling convention based on human inhalability.The first, and historically important, was by the International Standards Organization (ISO) ,5 which proposed a curve described by the empirical expression based on available data which, at the time (the late 1970s), included da, values only as high as 30 pm. In this expression dae is in micrometres and the aspiration efficiency for the human head is represented by inhalability ( I ) . The curve is shown in Fig. 1. The subsequent availability of a more comprehensive data set provided the basis for the proposal of a revised curve.6 In the recommendations of the American Conference of Governmental Industrial Hygienists (ACGIH) ,7 this new curve was adopted as a convention for defining the inhalable fraction and described by the empirical expression I = 0.5 [l + exp (- 0.06 d a e ) ] (2) for da, (again expressed in micrometres) up to and including 100 pm, beyond which it is explicitly acknowledged that there is no information on which to base a firm recommendation.This curve is shown also in Fig. 1. In these IS0 and ACGIH proposals, attention has been focused primarily on particle size-selective criteria for sam- 0 50 100 Particle aerodynamic diameter dJpm Fig. 1 fraction ( I ) Conventional particle size selection curve for the inhalable pling in indoor workplaces where wind speeds even as high as 4 m s-l are uncommon. However, there are some outdoors workplaces where conditions might sometimes lie outside this wind-speed range. Further, at least as far as the IS0 is concerned, sampling in the ambient atmosphere for the purpose of evaluating the risk to the community at large is an important part of its general remit. From the more recent experimental evidence,4 it is clear that the existing I S 0 and ACGIH conventions do not properly represent what happens at those higher wind speeds.In particular, the experimental data suggest that using samplers with performance based on either of these curves could lead to a significant underestimation of the exposure of humans to large particles. This could be important in situations where there are large particles containing potentially hazardous substances (e.g., radioactive nuclides, heavy metals, polycyclic aromatic hydrocarbons). It is therefore appropriate to consider how the definition of inhalability might be extended.With this in mind, a new convention has been proposed, based on a simple modification of the old ACGIH curve, along the lines I = 0.5 [l + exp(-0.06 dae)] + B where the wind-speed-dependent term B is given by B = 10-5 P.75 exp(0.55 dae) (3) (4) where U (m s-1) is the wind speed. This modified curve is being incorporated into a revised set of I S 0 proposals. At the time of writing, considerable progress has been achieved on harmonization of the I S 0 and ACGIH proposals, in particular agreement that the ACGIH curve should be universally adopted for workplaces. Now discussion is focus- ing increasingly on the practicalities by which the curve described (and also the equivalent curves for health-related finer fractions) might be used as a ‘yardstick’ for the performances of sampling instruments.In general, the defini- tion of a curve for defining a particular aerosol fraction raises the difficult question of how we decide whether or not the performance of a given instrument in relation to the conven- tion is acceptable. At first glance, ‘acceptability’ might be defined simply by requiring that an instrument’s performance curve falls within the specified tolerance band. However, herein lies a potential problem. As may be demonstrated numerically for aerosol samplers with performance charac- teristics apparently matching fairly closely a given convention, and for ranges of typical workplace aerosol particle size distributions, the collected mass of that particular aerosol fraction can vary enormously. This therefore alerts us to the general need, when testing aerosol samplers in relation to specific particle size-selective criteria, to take account not only of the proximity of data points to the ‘target’ curve but also the implications for errors in mass measurement dependent on particle size distribution. Some progress has been achieved in understanding the nature and magnitude of the problem.* However, further work is needed to achieve a practical solution. In the meantime, the best that can be recommended is that we should continue to judge sampler performance on the basis of its proximity to the specified curve, but that we should be vigilant to the errors that can arise and the conditions under which they can become significant.Strategies for the Sampling of Coarse Aerosols Health-related aerosol measurement in general, whether it be for coarse or for finer aerosol fractions, needs to be carried out with regard not only to such particle size-selective criteria but also to (a) the kinetics of the processes by which the particles can cause harm after inhalation and (b) the variability of exposure.Rappaport9 has recently addressed these factors in relation to occupational exposure. From such considerations,Analyst, January 1994, Vol. 119 15 it is clear that, for aerosols, we should be concerned not only with choices about the particle size selectivity of measuring instruments but also with the duration and frequency of sampling. For some workplace aerosols, the biological effects of exposure for short periods at high concentration may be severe and rapid.For these, sampling should be of appro- priately short duration and at relatively frequent intervals. On the other hand, for most aerosols encountered in workplaces, such biological processes are relatively long-term so that the effects of short-term high exposures are strongly damped out by the body’s defence mechanisms. For such aerosols, the sampling strategy may be based on longer duration (typically full-shift 8 h TWA) and less frequent measurements. In any given sampling exercise, there remains the further question about how best to reflect the true exposures of individual workers (or of groups of workers), either static (or area) measurement, where the chosen instrument is located in the workplace atmosphere and provides a measurement of the ambient aerosol concentration, or personal measurement , with the chosen instrument mounted on the body of the exposed subject and moving around with him or her at all times.When choosing one or other of these alternatives, some important considerations need to be taken into account. For a few workplaces (e.g., some working groups in longwall mining), it has been shown that reasonably good comparison may be obtained between suitably placed static instruments and personal samplers. More generally, however, static samplers have been found to perform less well, tending to give aerosol concentrations that are consistently low compared with those obtained using personal samplers. One advantage with static samplers is that a relatively small number of instruments may be used to survey a whole workforce.If this can be shown to provide valid and representative results, it is a simple and cost-effective exercise. Further, the high flow rates that are acceptable for static samplers mean that, even at very low aerosol concentrations, a relatively large sample mass can be collected in a short sampling period. In contrast, the use of personal samples is more labour intensive, requiring more instruments and hence greater effort in setting them up and in recovering and analysing the samples afterwards. Further, it involves the direct co-operation of the workers themselves. Also, for such samplers, it is inevitable that the capacities of the pumps used will be limited by their portability.Hence flow rates will usually be low (usually less than 4 1 min-1). However, personal aerosol sampling is widely accepted as the only reliable means of assessing the true aerosol exposures of individual workers. This is therefore by far the most common mode of aerosol measurement adopted by industrial hygienists. Implications of New Sampling Criteria for Limit Values As already stated, a limit value is prescribed in terms of an appropriately time-weighted average (TWA) airborne concentration of a given fraction of a given aerosol above which ‘unacceptable’ health risks may occur if exposure occurs at that level ‘day-after-day’. In addition, however, for some substances where exposure can lead to acute health effects, maximum exposure (or ceiling) limits (MELs) are assigned, indicating levels of exposure which should not be exceeded under any circumstances.The American (ACGIH) list of threshold limit values (TLVs) is highly influential, not only in the USA but also in many other countries. In that list, limits are suggested for a wide range of substances that can appear as aerosols. Regarding coarse aerosols, the TLV list currently recom- mends limits for ‘total’ aerosol only, although progress is being made in many countries towards a change to inhalability- based limit values. In the UK, the Health and Safety Executive (HSE) has already taken that step. There, in the occupational exposure standards (OESs, generally equivalent to the American TLVs), the old ‘total’ aerosol concept has been replaced by the inhalability criterion and options for suitable sampling instrumentation have been clearly identi- fied.It is noted that limit values for many types of coarse aerosol are the same for both ‘total’ and inhalable aerosol in the American and British lists, respectively. This poses an interesting problem since, although such numbers were usually derived from the same source, they are now subject to different measurement criteria. This was highlighted during a recent Swedish study,lO which compared individual dust exposures of flour mill workers using two different personal sampling instruments, one of the type widely used in the USA for ‘total’ aerosol and the other a new sampler with performance conforming to the inhalability criterion. The results showed that, on average, the inhalable aerosol sampler collected about twice as much mass as the ‘total’ aerosol sampler.Such a difference is strongly dependent on the particle size distributions of the aerosol studied, and so will vary substantially from one workplace situation to another. Hence the actual result in the flour mills should not be generalized directly to other industries. However, it is likely that the broad trend will be the same elsewhere; indeed, results just beginning to emerge from studies in other industries appear to be consistent with this expectation. This new knowledge carries the implication that it is inappropriate, for a given substance, to assign the same numerical limit value in lists of limit values where the underlying criteria are different (e.g., the American and British lists).Practical Sampling for Coarse Aerosols in Workplaces Static (or Area) Samplers for ‘Total’ or Inhalable Aerosol Static (or area) samplers have been used for many years in the sampling of coarse aerosol in workplace atmospheres. The simplest are open-filter arrangements mounted on the box which contains the pump (see Fig. 2) or systems in which the open-filter holder is mounted independently. The sampler shown is widely used in the UK, sampling at flow rates up to lo0 1 min-1. Similar devices have been used elsewhere, both in workplace and in ambient air sampling. So too have many other forms of static device, including the widely used (and aptly named) ‘Hi-Vol’ sampler. The performances of such Fig. 2 Typical open-filter arrangement of the type widely used for the static sampling of coaise aerosol in the UK (shown in the pump-mounted version with a recommended flow rate of 60 1 min-1)“16 Analyst, January 1994, Vol.119 instruments, originally intended as samplers for ‘total’ aerosol, should now be assessed in the light of the latest health-related particle size-selective criteria described earlier. The available data suggest that none of them adequately matches the inhalability criterion.11 Ideally, the design of sampling instruments for sampling the inhalable fraction should be based on a detailed knowledge of the physical processes by which particles are aspirated from the air into the instrument itself. Despite the fact that we have a fairly good appreciation of what happens for thin-walled sampling probes (such as those used for so-called isokinetic sampling in stacks and ducts) and other very simple sampler configurations, theory has not yet reached the stage where it can be applied to the types of device which might typically find application in aerosol sampling in the industrial hygiene context. This is an area where further work is clearly needed.In the meantime, the design of new practical sampling instruments matching the latest particle size-selective criteria has been, and continues to be, largely empirical and based on trial-and-modification. Nevertheless, new generations of aerosol sampler are beginning to appear, designed from the outset to match the inhalability criterion. One intended for use in workplaces is the 3 1 min-1 Institute of Occupational Medicine (IOM) static inhalable aerosol sampler (shown in Fig.3). 12 It incorporates a number of novel features. First, the sampler contains a single sampling orifice located in a head which, mounted on top of the housing containing the pump, drive and battery pack, rotates slowly about a vertical axis. In this way sampling is carried out whilst the orientation of the entry with respect to the wind is uniformly averaged. Hence it is analogous to the manner in which the inhalability curve had been defined for the human head. The entry orifice forms an integral part of an aerosol-collecting capsule which is located mainly inside the head. This capsule also houses the filter. In the use of the instrument, the whole capsule assembly (tare weight of the order of a few grams) is weighed before and after sampling to provide the full mass of aspirated aerosol.This system eliminates the possibility of errors associated with internal wall losses of the type described earlier. When the capsule is mounted in the sampling head, the entry itself projects about 2 mm out from the surface of the head, creating a ‘lip’ around the orifice itself. This has the effect of preventing the secondary aspiration of any aerosol particles which strike the outside surface of the head and fail to be retained. The performance of this sampler, shown in Fig. 4, is in fairly good agreement with the inhalability curve for particles with d,, up to about 100 pm for wind speeds up to 3 m s-1. At present this is the only static sampler specifically for the inhalable fraction which is commercially available (from Negretti Automation, Aylesbury, UK) , although prototype higher flow rate versions were built at the Institute of Occupational Medicine in Edinburgh during the late 1980s, and have subsequently been tested at Warren Spring Laboratory (Stevenage, UK) as possible candidate samplers for atmospheric suspended particulate matter.Personal Samplers for ‘Total’ or Inhalable Aerosol For reasons outlined above, personal sampling is generally the preferred approach for workplace aerosols. Here, for coarse aerosol, a large number of different devices have been used, again originating, historically, for the purpose of sampling for ‘total’ aerosol. Again, the simplest is the open filter arrange- ment, that shown in Fig.5 being the 25 mm open filter used in the UK by occupational hygienists in some applications. Other personal samplers for ‘total’ aerosol currently in use in the UK are the single (4 mm) hole sampler recommended by the HSE for lead aerosol and the modified seven-hole version recom- mended for general coarse aerosol sampling. These are also shown in Fig. 5. Both of these closed-face samplers also employ 25 mm filters. All three samplers are intended for use at a sampling flow rate of 2 1 min-1. 1 .o C 0.5 0 O . A O 9 A A A 50 1 00 Particle aerodynamic diameter d,&m Fig. 4 Sampling efficiency (shown here as A) of the IOM static inhalable aerosol sampler as a function of particle aerodynamic diameter for a range of relevant wind speeds.12 (Also shown for the purpose of comparison is the ACGIH inhalability curve.) U: 0,l and A , 3 m s-1 (a 1 (b ) (c 1 Fig.5 Three personal samplers of the type widely used for sampling coarse aerosol in the UK:13 (a) open filter holder; (b) single-hole sampler; and (c) seven-hole sampler. Recommended sampling flow rate for each is 2 1 min-1 Fig. 3 The IOM 3 1 min-1 static sampler for inhalable aerosol12Analyst, January 1994, Vol. 11 9 17 Experiments have been conducted to compare their per- formances with the inhalability curve.13 It is particularly important to note here, and for all the other personal samplers discussed below, that only data obtained with each sampler tested whilst mounted on a life-size torso (e.g., of a manne- quin) are considered useful in this context.It should not be assumed that, if such samplers were to be tested whilst located independently, they would necessarily provide the same results. It follows as a general principle that devices designed as personal samplers should not be used in the static mode. The results reported by Mark and Vincent13 for the three samplers in Fig. 5 indicate that all match the inhalability criterion fairly well for particles with d,, up to about 15 pm and for wind speeds of 1 m s-1 and below. However, for conditions outside these ranges, yet typical of those found in many workplaces, the performances are less satisfactory, with a strong wind-speed dependence (especially for the single-hole and seven-hole samplers) and with a tendency towards undersampling. Interestingly, it was found that the per- formances of these, and indeed other personal samplers, are not strongly dependent on where the device is mounted on the torso.Fig. 6 The 37 mm cassette of the type widely used in the US for the personal sampling of coarse aerosol. Recommended sampling flow rate is 2 1 min-1 The physical and design features of these three samplers are, in one way or another, representative of those exhibited by most of the many others which have been designed and used over the years in many countries. One is the 37 mm plastic cassette which is employed widely, either open-faced or closed-faced, by occupational hygienists in the USA (see Fig. 6). Test results for this sampler are limited in number and range of d,, covered,l4 but they are sufficient to suggest similar trends as for the samplers shown in Fig. 5, in particular that this sampler also provides a fair measure of the inhalable fraction for particles with d,, less than about 15 pm, but again tends to undersample for the large particles.In the light of the generally poor performances of many existing ‘total’ aerosol samplers with respect to the inhalability criterion, a new personal sampler has been proposed.13 This is the 2 1 min-1 IOM personal inhalable aerosol sampler (see Fig. 7). It features a 15 mm diameter circular entry which faces directly outwards when the sampler is worn on the torso. Like the IOM static inhalable aerosol sampler in Fig. 4, the entry is incorporated into an aerosol-collecting capsule which, during sampling, is located behind the face-plate.Use of this capsule ensures that the over-all aspirated aerosol is always assessed. Also, as for the static sampler, the lips of the entry protrude outwards slightly from the face-plate in order to prevent oversampling associated with particle blow-off from the external sampler surfaces. Experimental data for this instru- ment are shown in Fig. 8, and they show a good match with the inhalability curve for particles with d,, up to 80 pm and for wind speeds up to 2.6 m s-1. Again, as for the IOM static inhalable aerosol sampler, this instrument is the only one currently available commercially (from SKC, Blandford Forum, Dorset, UK) that is known to match adequately the inhalability criterion. Conclusion During the past decade or so, great progress has been made towards placing the health-related sampling of coarse work- place aerosols on a more rational footing.In particular, recognition of the inconsistencies of the old ‘total’ aerosol approach and the emergence of a new criterion based on human inhalability have been great steps forward. The wide degree of international agreement has been most reassuring, and some regulatory bodies have begun to adopt the new approach. However, its wider acceptance as the basis of standards is tempered in some quarters by fears of the possible implications for limit values (as suggested earlier). Mean- while, the current commercial availability of appropriate instrumentation should expedite full implementation of the inhalability criterion and hasten the development of new and I I i + Fig.7 The IOM 2 1 min-l personal sampler for inhalable aerosol.l3 (Photograph supplied by courtesy of SKC) 0 20 40 60 80 Particle aerodynamic diameter d,&m Fig. 8 Sampling efficiency (shown here as A ) of the IOM personal inhalable aerosol sampler as a function of particle aerodynamic diameter for a range of relevant wind ~peeds.1~ Also shown for the purpose of comparison is the ACGIH inhalability curve. U: 0, 0.5; 0, 1.0; and +, 2.6 m s-118 Analyst, January 1994, Vol. 119 improved standards. Indeed, there appears to be no justifica- tion for further delay. At the same time, the adoption of the proposed new framework for standards would stimulate the development of further new, and improved, instruments. References Ogden, T. L., and Birkett, J. L., in Inhaled Particles IV, ed. Walton, W. H., Pergamon Press, Oxford, 1977, pp. 93-105. Vincent, J. H., and Mark, D., in Inhaled Particles V , ed. Walton, W. H., Pergamon Press, Oxford, 1982, pp. 3-19. Armbruster, L., and Breuer, H., in Inhaled Particles V , ed. Walton, W. H., Pergamon Press, Oxford, 1982, pp. 3-19. Vincent, J. H., Mark, D., Miller, B. G., Armbruster, L., and Ogden, T. L., J. Aerosol Sci., 1990,21,577. International Standards Organization, Air Quality-Particle Size Fraction Definitions for Health-related Sampling, Technical Report ISO/TR/7708-1983 (E), ISO, Geneva, 1983. Vincent, J. H., and Armbruster, L., Ann. Occup. Hyg., 1981, 24,245. 7 8 9 10 11 12 13 14 ~~~ ~ American Conference of Governmental Industrial Hygienists (ACGIH), Particle Size-selective Sampling in the Workplace, Report of the ACGIH Technical Committee on Air Sampling Procedures, ACGIH, Cincinnati, OH, 1985. Kenny, L. C., J. Aerosol Sci., 1992,23,773. Rappaport, S . M., Ann. Occup. Hyg., 1990,35,61. Lillienberg, L., and Brisman, J., in Inhaled Particles VZZ, in the press. Mark, D., Vincent, J. H., Stevens, D. C., and Marshall, M., Atmos. Environ., 1986,20,2389. Mark, D., Vincent, J. H., and Gibson, H., Am. Znd. Hyg. Assoc. J., 1985,46, 127. Mark, D., and Vincent, J. H., Ann. Occup. Hyg., 1986,30,89. Buchan, R. M., Soderholm, S. C., and Tillery, M. I., Am. Znd. Hyg. Assoc. J., 1986,47,825. Paper 31032OOK Received June 4, 1993 Accepted August 17, 1993

ISSN:0003-2654    

DOI:10.1039/AN9941900013

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Analyst, January 1994, Vol. I I9 19 Measurement of Fine Aerosols in Workplaces* A Review James H. Vincent Division of Environmental and Occupational Health, School of Public Health, University of Minnesota, Box 807 Mayo, 420 Delaware Street SE, Minneapolis, MN 55455, USA The fine aerosol fractions of interest in occupational health are those associated with the regional deposition of inhaled aerosols in the different parts of the human respiratory tract. The recent recommendations of the International Standards Organization, the American Conference of Governmental Industrial Hygienists and the Comit6 Europetin de Normalisation define the thoracic fraction (inhaled particles which penetrate into the lung) and the respirable fraction (inhaled particles which penetrate further into the alveolar region).Based on the results of inhalation experiments with humans, conventional curves for these fractions are proposed, which provide ‘yardsticks’ for health-related sampling devices. Samplers for the respirable fraction have been in existence since the early 195Os, and a fairly large range of acceptable instrumentation is available commercially. Recently, however, attention has been drawn to the effect of even small departures from the ‘target’ curve on the respirable mass sampled. This suggests the need for additional criteria for sampler acceptability, based on sampled mass in addition to particle size selectivity. Samplers for the thoracic fraction may be based on similar physical concepts to those for respirable aerosol. In addition, versatile devices capable of providing information about more than one fraction simultaneously are being proposed and are finding increasing use as investigative tools for industrial hygienists.Finally, measurement of fine fibrous aerosols is recognized as a special case, and so is treated separately. Keywords: Fine aerosols; workplace monitoring Introduction The preceding paper1 sets out the background describing the nature of aerosol exposure in workplaces and the ideal basis of standards aimed at protecting workers. It then goes on to describe the rationale and variety of technical options for the sampling and measurement of coarse aerosol-the inhalable fraction (previously referred to as ‘total’ aerosol). This paper proceeds to extend those ideas to the measurement of fine health-related aerosol fractions.The Human Respiratory Tract The human respiratory tract is a complex system, its primary objective being to supply the body with oxygen (during inhalation) and to eliminate carbon dioxide (during exhala- tion). For the present purposes, a rudimentary description is sufficient. As shown in Fig. 1, the inhaled air enters the respiratory tract through either the nose or the mouth. It first encounters the upper region of the respiratory tract, compis- * Presented at the Conference on Modern Principles of Workplace Air Monitoring: Pumped and Diffusive Sampling for Contaminants, Geilo, Norway, February 15-18, 1993. ing the airways of the nose and mouth which, together, form the nasopharynx. The over-all ‘head’ region is assumed in the present context to include both the nasopharynx and the larynx.The whole region below the larynx is the lung, referred to as the thoracic region. Air enters through the larynx into the trachea, which in turn leads to a branching system of conducting airways referred to as bronchi and, eventually, the conducting and terminal bronchioles. Beyond the terminal bronchioles is the alveolar region where the gas exchange takes place. This consists of the respiratory bronchioles, alveolar ducts and alveolar sacs. Aerosol Regional Deposition in the Respiratory Tract The first part of the process of aerosol exposure occurs during the entry of particles into the respiratory tract during inhalation. The second part involves the arrival of particles at relevant sites inside the respiratory tract as the result of deposition by a combination of physical mechanisms (includ- ing sedimentation, impaction, diffusion and electrostatic forces). This has been investigated by aerosol inhalation experiments involving human volunteer subjects.Such experi- ments have permitted the determination of the, probability of deposition as functions of partical aerodynamic diameter (d,,) in the extrathoracic (nasopharyngeal), tracheobronchial (the conducting airways) and the alveolar regions. The efficiency of thoracic deposition is defined as amount deposited in tracheobronchial + alveolar regions amount inhaled Cthor = (1) Based on typical data from the literature,2-4 this is shown as a function of d,, in Fig. 2. The efficiency of alveolar deposition is amount deposited in the alveolar region amount inhaled G I ” = (2) Nasopharynx Larynx Trachea Bronchi Bronchioles Alveoli Fig.1 Simplified schematic diagram of the human respiratory tract20 Analyst, January 1994, Vol. I 1 9 for which typical data2 are shown in Fig. 3. These show that Calv falls to zero for particles with d,, larger than about 10 pm, reflecting the non-availability of larger particles due to the filtration effect of the upper respiratory tract. As d,, decreases, Calv exhibits a maximum around d,, = 3 ym, then decreases again. Although not revealed by the data as plotted, Calv reaches a minimum at around d,, = 0.5 pm then rises again for still smaller particles (as a result of increasing particle deposition by diffusion).The dip in Calv for dae below about 3 pm represents the exhalation of undeposited particles. It should be noted that none of the above relates to fibrous aerosols. Because there have been no experiments with human subjects for such substances (because of the very significant health risk that is associated with the fibrous and, frequently, durable nature of such particles), there are no data which correspond to those for non-fibrous particles. Criteria for the Measurement of Finer Aerosol Fractions The experimental data in Fig. 2 provided the basis of the conventional curve for thoracic aerosol proposed in 1983 by 10 20 30 Particle aerodynamic diameter d,&m Fig. 2 Typical experimental data (for human subjects) for thoracic deposition; also shown is the conventional particle size-selection curve for the thoracic fraction6 1 - 8 2 8 5 .E 0.5 8 2 a, 0 5 Particle aerodynamic diameter d&m Fig.3 Typical experimental data (for human subjects) for alveolar deposition; also shown are various conventional curves for the respirable fraction: A, the BMRC curve;5 B, the 1985 ACGIH curve;6 and C, the proposed new curve7 the International Standards Organization (ISO)5 and in 1985 by the American Conference of Governmental Industrial Hygienists (ACGIH);6 it is the same for both. This curve takes the form of a cumulative log-normal function with its median at dae = 10 pm and having a geometric standard deviation (a& of 1.5. It is seen from Fig. 2 that the conventional curve lies above the majority of the data points, the rationale being that, if anything, the conventional curve should err on the side of the ‘worst-case’ situation.Of the thoracic aerosol that penetrates below the larynx, a further subdivision takes place between what is deposited in the tracheobronchial region and that which penetrates down to the alveolar region. The fine fraction penetrating down to the alveolar region is known as the respirable fraction. In Fig. 3 are shown, alongside the alveolar deposition data from experiments with human subjects, a number of the curves that have been adopted over the years as conventions for the respirable fraction. These include the historically important British Medical Research Council (BMRC) curve, which first emerged in the early 1950s, and the 1985 ACGIH curve. Also shown is the new version proposed as a basis for international harmonization on the matter.7 Again, it is noted that none of these conventional respirable aerosol curves truly reflect alveolar deposition at very small particle sizes.This does not pose a problem so long as the aerosol in question does not contain a significant proportion of its mass in particles of diameter below about 1 pm. However, caution should be exercised in applying such respirable aerosol conventions to mixed aerosols where there are important components falling almost entirely in the sub-micrometre particle size range (e.g., diesel fume in the presence of dust). The latest criteria for health-related aerosol standards, representing the results of harmonization between IS0 and ACGIH, and latterly the ComitC Europe& de Normalisation (CEN), include recognition of the various processes by which aerosols come into contact with the human respiratory system.These reflect (a) aerodynamic processes outside the body by which particles are inhaled through the nose andor mouth and (b) aerodynamic processes inside the body whereby those inhaled particles are deposited. Thus inhaled aerosol is seen to be a fraction of the true total workplace aerosol. In turn, thoracic and respirable aerosol are sub-fractions of the inhalable fraction. For the fine aerosol fractions, there is now general agreement (led by ISO, ACGIH and CEN) on the following quantitative definitions: For the thoracic fraction, described as a sub-fraction of inhalable aerosol, the median d,, value for the cumulative log-normal curve is 11.45 pm and the geometric standard deviation (og) is 1.5; this means that, as a fraction of true total aerosol, the median dae value would be 10 pm, as described in the 1983 I S 0 and 1985 ACGIH recommendations.For the respirable fraction, again described as a sub-fraction of inhalable aerosol, the median for the cumulative log- normal curve is d,, = 4.25 pm and the geometric standard (og) is again 1.5; this means that, as a fraction of true total aerosol, the median d,, value would be 4 pm. In the new recommendations, tolerance bands are defined as before. However, as already discussed,’ the practical application of such tolerance bands in assessing the accept- ability of a given sampling instrument is not sufficient alone. In practice, ‘acceptable performance’ must be defined by also requiring that an instrument’s performance allows the collec- tion of aerosol mass which, under expected practical condi- tions, falls sufficiently close to what would be expected using a ‘perfect’ sampler.How to achieve this within a framework for an overall performance standard is still under consideration .g Fine fibrous aerosols can, as already mentioned, pose a particularly serious risk to health, and so represent a specialAnalyst, January 1994, Vol. 119 21 problem for the occupational hygienist. Asbestos-containing dusts come into this category. Because of their unusual morphological characteristics, such fibres are specifically not included in the above conventions. Instead, there are different criteria for measurement, based on an appreciation of both the aerodynamic characteristics of particle motion which govern fibre deposition in the deep lung and the biological effects that can then ensue and govern the subsequent fate of the particles.With these equally important factors in mind, it has been a common convention, since the 1960s, to assess ‘respirable’ fibres in terms of the airborne number concentration of particles which, when examined by optical microscopy under phase contrast conditions, have an aspect ratio greater than 3, a length greater than 5 pm and a diameter less than 3 pm, as recommended, for example, by the Asbestos International Association (AIA) .9 Standards Based on Fine Aerosol Fractions One health-related class of aerosols is for particles that may lead to adverse health effects after deposition in the tracheo- bronchial region of the lung.In this category are substances that can provoke local responses leading to such effects as bronchoconstriction, chronic bronchitis and bronchial carci- noma. For the health-related measurement of such aerosols, it is appropriate to think in terms of sampling according to a tracheobronchial criterion. However, for practical purposes, the overall thoracic fraction is more convenient to define and measure, and is sufficient. Another class is for particles that deposit in the alveolar region of the lung. Here local effects include the pneumo- conioses (e.g., silicosis and asbestosis), emphysema, alveolitis and pulmonary carcinoma. In relation to these, the respirable aerosol fraction represents a convenient and appropriate sampling criterion. As discussed previously for the inhalable fraction,l any such criteria need to be applied within sampling strategies that best reflect individual worker exposures to health-related sub- fractions and reflect the dynamics of possible health effects as well as the variability of exposure.Sampling for Fine Aerosol Fractions The history of sampling fine aerosols in workplaces began with the respirable fraction, in particular with the emergence in the 1950s of the BMRC respirable aerosol criterion. A number of types of sampling device have since been developed. Most have in common the fact that they first aspirate a particle fraction which is assumed to be representative of the total workplace aerosol, from which the desired fine fraction is then aerodynamically separated inside the instrument using physical options (e.g., elutriation, cyclone) with particle size-dependent penetration characteristics matching the desired criterion.The fine fraction of interest is that which remains uncollected inside the selector and passes through to collect on to a filter or some other collecting medium. Static (or Area) Samplers for the Respirable Fraction According to the philosophy embodied in the latest sampling criteria, if an instrument is to be used for collecting a fine aerosol fraction corresponding to deposition in a particular region of the respiratory tract, it should (ideally) first aspirate the inhalable fraction. Otherwise, if a sampler has a poorly defined aspiration efficiency, or one which varies in an uncontrolled way with (say) wind speed or orientation, then bias can result in the determination of the fine fraction of interest.Therefore, in samplers intended primarily for deter- mination of finer fractions, it is relevant to consider their aspiration efficiency in relation to the inhalability criterion. Static samplers commonly used in Europe for sampling the fine respirable fraction include, for example, the British 2.5 1 min-1 MRE Type 113A (see Fig. 4) with a pre-selector based on horizontal elutriation principles, and the German 50 1 min-1 TE3F50 (not shown) with a pre-selector based on the cyclone. Both were developed for applications in coal mines. Data for the aspiration efficiency of these instruments show that neither instrument matches the inhalability criterion particularly well for particles in the coarse size range exceeding about 10 pm.10 However, for finer particles in the respirable range, the agreement is much better.Here, reasonable consistency with the ideal inlet efficiency require- ment embodied in the latest sampling recommendations is maintained under most conditions. However, results for the performance of the MRE instrument in relation to the collection of respirable dust do show a strong dependence on wind speed, especially above 5 m s-1.11-13 These strongly suggest the onset of significant changes in aspiration efficiency at higher wind speeds. Caution is therefore recommended in interpreting respirable dust data, obtained using such instru- ments under these conditions.Regarding their performance for the finer respirable fraction, experimental results for the internal selection properties of both the above instruments are in good agreement with the BMRC curve. Personal Samplers for the Respirable Fraction Horizontal elutriators have been found to be very satisfactory for static respirable aerosol sampling, but they are inevitably rather bulky and not conducive to miniaturization. Therefore, horizontal elutriation is not promising for personal respirable (4 Parallel plate elutriator Glass-fibre membrane Filter clip reservoir - / - Terylene backing filter Adjustable crank \/ Valves Fig. 4 British MRE Type 113A static sampler for respirable aerosol (sampling flow rate 2.5 1 min-I), with pre-selector based on the horizontal elutriator principle22 Analyst, January 1994, Vol.119 aerosol samplers. On the other hand, cyclones are ideally suited for such purposes, and so have found wide application. Well known examples are the British 1.9 1 min-1 Casella cyclone (see Fig. 5) and the equivalent American 1.7-2.1 1 min-1 10 mm cyclone (not shown). Experimental data for their selection characteristics are in good agreement with the BMRC and ACGIH curves, respectively. Unfortunately, there are no aspiration efficiency data available for such samplers. However, based on the experience gained for other types of sampler, it is reasonable to assume that the aspiration efficiency will follow the inhalability curve fairly well for fine particles in the respirable size of primary interest in the use of these devices.Fig. 5 The 1.9 1 min-1 cyclone-based personal sampler of the type widely used for respirable aerosol in the UK There are two other devices that have emerged relatively recently as samplers primarily for finer aerosol fractions, having some interesting and unusual features and so deserving special mention. The first is the French CIPlO14 (see Fig. 6). It is particularly interesting because it incorpor- ates its own built-in pumping unit, consisting of a battery- driven, rapidly rotating polyester foam plug. Aerosol is aspirated through a downward-facing annular entry and is collected efficiently by filtration in two stationary, coarse- grade plastic foam plugs located inside the entry as well as on the finer-grade rotating plug.As a result of the low pressure drop characteristics of such foam filtration media, a flow rate of up to 10 1 min-1 can be achieved. By personal sampler standards, this is very large indeed. For this device, the fine-fraction pre-selector operates on the basis of foam filtration, where aerosol entering porous polyester foam media is collected by a combination of gravitational settling and inertial forces. Experimental data for the fine aerosol selection characteristics of the CIPlO lie approximately midway between the BMRC and ACGIH curves, and so come close to matching the new curve for the respirable fraction. One interesting feature of the CIPlO is the observed decrease in penetration for small particles with dae less than about 3 pm.This is the result of the penetration of fine particles through the final rotating collector foam (and so their escape from the instrument). This feature brings the performance of the CIPlO more closely into line with true alveolar deposition than any of the other respirable aerosol samplers described. The second interesting personal sampler is the Italian PERSPEC, a device aimed at collecting not only total aerosol but also the finer thoracic and respirable fractions (see Fig. Fig. 6 French CIPlO personal sampler for respirable aerosol.14 It contains its own air moving apparatus and operates at a sampling flow rate of 10 1 min-1 Fig. 7 Italian PERSPEC personal sampler,15 developed primarily as a sampler for the fine thoracic and respirable fractions, but also having potential for use for inhalable aerosol.Sampling flow rate is 2 I min-lAnalyst, January 1994, Vol. 11 9 23 7).15 Aerosol enters at 2 1 min-1 through a pair of crescent- shaped orifices and is separated by inertial forces into the finer sub-fractions of interest (which are deposited on different, well defined parts of the same filter). Sampling for ‘Respirable’ Fibres Because the definition of a ‘respirable’ fibre is based on purely geometric criteria, selection is best carried out not aerody- namically but visually under the microscope. This means that, in practical sampling, the main priority is to achieve deposition on a suitable surface (e.g., a membrane filter), which can then be ‘cleared’ and mounted for subsequent visual analysis by optical microscopy under phase-contrast conditions.It follows that actual physical sampling can be very simple, usually involving the collection of particles directly on an open filter (sometimes with the use of a cowl or some other baffle to protect the filter from large airborne material). Such sampling is carried out routinely in both the static and personal modes. In asbestos measurement, great emphasis is placed on the visual assessment of the sampled fibres. For routine assess- ment of workplace asbestos, this is usually carried out using an optical microscope under phase-contrast conditions at a magnification of ~ 4 5 0 . An appropriate graticule is used to provide ease of classification of fibres matching the criteria referred to earlier.Sets of ‘counting rules’ have been recommended to aid the microscopist in what, and what not, to count, guiding, for example, the assessment of fibrous aggregates, fibres in the presence of other, non-fibrous particles and fibres not fully contained within the microscope field of view. The technical methods for sample preparation and microscopy and the processes of selecting and counting fibres have been extensively researched and fully documented in the various reference methods that have been published.9 One important practical aspect is the setting of the sampling flow rate, as sufficient flow is required to achieve, over a sampling shift, a sample that is dense enough to provide good counting statistics and reliable visual counting,16 yet not so dense as to cause problems with fibre overlap.17 As far as the effects of sampling flow rate on aspiration efficiency for fibres are concerned, it has been demonstrated that, over a very wide range of flow rates, fibrous particles of asbestos are so fine that aspiration efficiency is nearly always close to unity.18 Therefore, for practical purposes, sampling bias due to aspiration effects can be neglected, providing considerable flexibility in the choice of flow rate in a given situation.Sampling for More Than One Fraction Simuhneously The important concept that thoracic aerosol is a sub-fraction of the inhalable fraction and that respirable aerosol is a further sub-fraction of the thoracic sub-fraction provides a framework by which all three aerosol fractions can be obtained simul- taneously.Such aerosol measurements could be important for assessing aerosol-related risk in certain situations, and appropriate practical sampling devices are just beginning to emerge. One interesting such personal sampler is the Italian PERSPEC already mentioned (see Fig. 7). A second instru- ment20-22 is derived directly from the Institute of Occupational Medicine (IOM) personal inhalable aerosol sampler (see Fig. 8)23 as described in the preceding paper.’ Here, aerosol is again aspirated through a 15 mm circular entry and, as before, the entry forms an integral part of an aerosol-collecting capsule which acts as a receptacle for the whole inhalable fraction. Now, however, the capsule is extended in length in order to house two porous polyester foam selectors, each using different grades of foam.The first is chosen ( i t ? . , grade of foam, dimensions) to provide penetration characteristics matching the thoracic fraction. The second selector, placed immediately behind the first, is chosen to provide penetration characteristics matching the respirable aerosol curve. In the practical use of this instrument, the whole capsule is weighed before and after sampling (to provide the inhalable mass fraction). Then the second (fine) foam plug and the backing filter are removed and weighed separately. The sum of the resultant two masses provides the thoracic mass fraction. The mass on the backing filter is the respirable mass sampled. This instrument is still at the prototype stage at the time of writing, so is not yet available commercially.Aerosol Spectrometers In principle, if we know the particle size distribution and the mass of the sampled aerosol, then we can determine the particle size distribution and mass contained in any sub- Sampling for the Thoracic Fraction Methodology for the sampling of thoracic aerosol in the occupational context was not widely considered prior to the emergence of the new IS0 and ACGIH criteria. For workplaces, the nearest we have come to a thoracic aerosol standard is in the US cotton industry, where a criterion was established in 1975 by the US National Institute of Occupa- tional Safety and Health (NIOSH), based on a selection curve which falls to 50% at 15 pm. This seems to imply recognition of the role of particle deposition in the large airways of the upper respiratory tract in cotton workers’ byssinosis.The recom- mended static sampling method employs the concept of vertical elutriation.19 Now, as the ISo and recommendations begin to be translated into new standards, more energetic consideration is Fig. 8 IOM 2 1 min-1 persona] sampler developed for the simu]- taneous sampling of inhalable, thoracic and respirable aerosol .20-22 It being given to the development of samplers for the thoracic fraction, and first attempts are being based On modification Of existing respirable aerosol samplers. incorporates an inhalable entry23 and two porous foam pre-selecton (located inside the nose-piece of the sampling head) operating on filtration principles24 Analyst, January 1994, Vol. 11 9 fraction.Aerosol spectrometers that can provide such infor- mation are more versatile than the dedicated samplers described above as they can provide data about any number of sub-fractions from just one sample. This can have important implications, in particular for epidemiological research. For example, in one recent study, the approach outlined above has been used to examine the effects on the actual dust uptakes (or deposited lung dose) in mineworkers of different breathing patterns, and hence different lung deposition characteristics, associated with different work rates.24 A wide range of physical possibilities exists upon which to base a family of aerosol spectrometer devices. The type that has achieved the greatest popularity since it first emerged in the 1940s is the cascade impactor.In this device, sampled aerosol passes through a succession of impactor stages, each taking the form of a jet directed on to a solid surface. Particle deposition takes place by impaction on to the surface, strongly dependent on particle aerodynamic size, jet width and jet air velocity. Decreasing jet width at each successive stage ensures that smaller and smaller particles are deposited as the aerosol penetrates from stage to stage. From the masses of aerosol collected at each stage, together with knowledge of the particle deposition (or ‘cut’) characteristics of the impactor stages, the cumulative and, in turn, the frequency size distribution of the sampled aerosol can be obtained. More detailed information of the principles, performances and types of cascade impactors and on data reduction appears widely elsewhere in the literature.Here just two specific instruments are mentioned. As they take the form of personal samplers, they are of particular potential value for applications in the investigation of aerosol- related occupational lung disease and, indeed, are finding increasing use as such. The first is the sampler proposed by Rubow et al.25 shown in Fig. 9 (the so-called ‘Marple’ device). It is an eight-stage device, with radial slot-shaped jets at each stage where aerosol is collected on polycarbonate membrane films. By weighing the films before and after sampling, the mass of aerosol collected on each is assessed gravimetrically. The second device is the IOM personal inhalable dust spectrometer (PIDS) shown in Fig.10.26 The general configu- ration is similar to that for Rubow et al.’s*5 device. exceDt that the slot jets are replaced with circular jets. The aerosol is collected directly on the back of each disc-shaped aluminium impactor surface, which also incorporates the jets for the next stage. All the collection surfaces are greased prior to sampling and the masses of collected aerosol are obtained by weighing each disc before and after. The key feature of this instrument that distinguishes it from the previous type is that it incorporates a 15 mm circular entry similar to that for the IOM inhalable aerosol sampler, so it begins by aspirating the inhalable fraction. This entry is incorporated into a ‘cassette’, which, by also weighing before and after sampling, provides the mass of aerosol that is collected between the entry and the first impactor stage.Using this mass together with knowledge of the penetration characteristics of the entry stage, the particle size distribution obtained from the cascade impactor part of the instrument may be corrected to allow for Fig. 9 an actual workplace situation. Photograph courtesy of Andersen Fig. 10 IOM 2 1 min-1 personal inhalable dust spectrometer Instruments, Atlanta, GA. Marple 2 1 min-1 personal cascade impactor,25 shown in use in (PI D S)2625 Analyst, January 1994, Vol. 11 9 deposition (of both coarse and fine particles) in the entry, thus providing the particle size distribution of the whole inhalable fraction. Conclusion At present, limit values (e.g., in the ACGIH threshold limit value list) for fine aerosols are assigned only for the respirable aerosol fraction.For practical workplace measurement of this fraction, existing instrumentation appears adequate to meet most of the requirements of the latest criteria under most practical conditions. It is believed that, to match the compro- mise curve proposed by Soderholm,7 minor adjustments in sampling flow rate will achieve the desired purpose. Regard- ing assessment of sampler acceptability, however, there remain questions as to the best protocol.8 Few instruments are available specifically for the thoracic fraction. However, sufficient knowledge exists about the performance of pre-selectors such as those used for the respirable fraction to permit the design of adequate samplers for the thoracic fraction as soon as the demand is stimulated (i.e., when limit values for appropriate substances are expressed in terms of the thoracic fraction). Finally, the role of aerosol spectrometers as investigatory tools for industrial hygienists has been clearly identified. References Vincent, J. H., Analyst, 1994, 119, 13. Lippmann, M., in Handbook of Physiology; Section ZV, Environmental Physiology, eds. Lee, D. H. K., and Murphy, S., Williams and Wilkins, Philadelphia, 2nd edn., 1977, pp. Chan, T. L., and Lippmann, M., Am. Znd. Hyg. Assoc. J., 1980, 41, 399. Stahlhofen, W., Gebhart, J., and Heyder, J., Am. Znd. Hyg. Assoc. J . , 1980, 41, 385. International Standards Organization, Air Quality-Particle Size Fraction Definitions for Health-related Sampling, Technical Report ISO/TR/7708-1983 (E), ISO, Geneva, 1983.213-232. 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 American Conference of Governmental Industrial Hygienists, Particle Size-selective Sampling in the Workplace, Report of the ACGIH Technical Committee on Air Sampling Procedures, ACGIH, Cincinnati, OH, 1985. Soderholm, S. C., Ann. Occup. Hyg., 1989,33, 301. Kenny, L. C., J. Aerosol Sci., 1992, 23,773. Asbestos International Association, Recommended Technical Method No. I : Reference Method for the Determination of Airborne Asbestos Fibre Concentrations at Workplaces by Light Microscopy (Membrane Filter Method) AIA, London, 1979. Vincent, J . H . , Aerosol Sampling: Science and Practice, Wiley , Chichester, 1989. Ford, V. H. W., Ph.D. Thesis, University of Newcastle-upon- Tyne, 1971. Ogden, T. L., Birkett, J. L., and Gibson, H., Improvements to Dust Measuring Techniques, IOM Report No. TM/77/11, Institute of Occupational Medicine, Edinburgh, 1977. Mark, D., Lyons, C. P., and Upton, S. L., Appl. Occup. Environ. Hyg., 1993, 8, 370. Courbon, P., Wrobel, R., and Fabries, J.-F., Ann. Occup. Hyg., 1988,32, 129. Prodi, V., Belosi, F., and Mularoni, A., J. Aerosol Sci., 1986, 17, 576. Cherrie, J. W., Jones, A. D., and Johnston, A. M., Am. Znd. Hyg. Assoc. J . , 1986,47, 465. Iles, P. J., and Johnston, A. M., Ann. Occup. Hyg., 1983, 27, 389. Johnston, A. M., Jones, A. D., and Vincent, J. H., Ann. Occup. Hyg., 1982,26,309. Walton, W. H., Br. J. Appl. Phys., 1954, 5 , Suppl., S29. Mark, D., Borzucki, G., Lynch, G., and Vincent, J. H., paper presented at the Annual Conference of the Aerosol Society, Bournemouth, 1988. Aitken, R. J., Vincent, J. H., and Mark, D., Appl. Occup. Environ. Hyg., 1993, 8, 363. Vincent, J. H., Mark, D., and Aitken, R. J., J. Aerosol Sci., 1993,24, 929. Mark, D., and Vincent, J. H., Ann. Occup. Hyg., 1986,30,89. Vincent, J. H., and Mark, D., Ann. Occup. Hyg., 1984,28,117. Rubow, K. L., Marple, V. A., Loin, J., and McCawley, M. A., Am. Znd. Hyg. Assoc. J . , 1987, 48, 532. Gibson, H., Mark, D., and Vincent, J. H., Ann. Occup. Hyg., 1987,31,463. Paper 3103201 I Received June 4, 1993 Accepted August 16, 1993

ISSN:0003-2654    

DOI:10.1039/AN9941900019

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Analyst, January 1994, Vol. 119 27 Performance Parameters for Assessing the Acceptability of Aerosol Sampling Equipment* Goran Lid& National Institute of Occupational Health, S-171 84 Solna, Sweden The European standardization organization (CEN) has been asked by the General Commission of the European Community to prepare standards for chemical agents in workplace atmospheres. The CEN Technical Committee 137 'Assessment of Workplace Exposure' has divided its work into working groups. Its main area of work is concentrated on sampling strategy; general performance requirements; sampling conventions for particulate matter; and performance requirements for gas and vapour sampling instruments, aerosol samplers, and personal sampling pumps. This paper presents the test procedure the CEN working group on particulate matter has proposed that shows how to evaluate the performance of aerosol samplers.The draft requirements on personal sampling pumps for dust sampling are also presented. The draft test procedure for aerosol samplers will be tested and evaluated in a pan-European test of samplers for inhalable dust, which is presented below (the study is ongoing). Keywords: Aerosol; performance; pumps; sampler; standardization Development of an Aerosol Sampler The modern approach of designing samplers from sampling conventions, rather than designating a specific existing sampler to be a reference sampler, irrespective of how it samples, is based on two factors: medicaVphysiologica1 knowledge of the human respiratory system and a conviction that it is technically possible to construct a sampler with the desired sampling characteristics.Although the human respiration system consists of many component parts, it may, from a medicaVphysiologica1 stand- point, be divided into three different regions with similar properties. The three regions are the head airways, the trachea and bronchi, and the alveolar region. These regions differ in function and surface tissues, air residence times, particle separation mechanisms and capacities, and clearance mechanisms.' The head airways act as an inlet and clean the inhaled air of large particles. Most deposited particles are cleared in a few minutes by sneezing or by swallowing, although some particles, e.g., those of hard wood can reside there for a long time and cause nasal cancer.2 The tracheo- bronchial region transports the air to the part of the lung where gaseous exchange takes place.The particle separation capacity here is low, and what has deposited is transported towards the mouth and swallowed within a few hours. In the alveolar region gas exchange between the air and the blood occurs. In this region only a small fraction of the air is changed with each breath, and hence the long residence time leads to considerable particle deposition. Deposited particles are either transported towards the bronchioles by macrophages, * Presented at the Conference on Modern Principles of Workplace Air Monitoring: Pumped and Diffusive Sampling for Contaminants, Geilo, Norway, February 15-18, 1993. dissolved in the blood, or moved into the blood or lymphatic systems.The removal time for these deposited particles may be up to a few months. From an aerosol sampling point of view, the human respiratory system may be considered as a sampling train consisting of an inlet, a pre-separator, a transport line with some losses, and a collection filter. For many years the regional particle deposition in the human respiratory system has been studied both experimen- tally and theoretically and the effects of particle size, breathing pattern, age, sex, individual variation, etc., have been measured.3-6 In the last 15 years experiments have also been performed to quantify the fraction of airborne particles that actually enter the respiratory system (the inhalability).7 Although deposition studies have been performed on humans, the inhalability studies have used breathing (in- and ex-haling) mannequins mounted in a wind tunnel.Using the results from the deposition studies it is possible to estimate an average human deposition as a function of particle size (and other human individual parameters) and to add on a safety margin in order to include a large fraction of the healthy working population. The inhalability studies on the other hand have mainly been assessed for a particular set of physiological conditions that correspond to light-to-medium work, however, the inhalability was found to have negligible dependence on small variations in breathing patterns. From a knowledge of the distribution of particle deposition in human breathing systems it is possible to formulate standards that represent a given fraction of the human population.Such a standard describes the fraction of particles in the ambient air that will reach a certain region in the respiratory system. The standards are called sampling conven- tions and the instruments used to sample any fraction ought to have a sampling efficiency as close to the sampling convention as possible. The European and international standardization organizations, and the American Conference of Governmen- tal Industrial Hygienists (ACGIH) have all agreed on identical sampling conventions for the three regions of the respiratory system ,8-10 based on Soderholm's review of deposition data." However, the sampling conventions are not defined as one convention per region. Instead they are defined cumulatively: the respirable convention for the alveolar region; the thoracic convention for the tracheo-bronchial and the alveolar regions; and the inhalable fraction for all three regions.The three sampling conventions are shown in Fig. 1 as functions of particle aerodynamic size. The main difference between the inhalable convention and the two other conventions, is that due to experimental difficulties the inhalable sampling con- vention is only known up to 100 pm (where it has not come down to zero sampling efficiency), whereas the respirable and thoracic conventions have a virtually zero sampling efficiency above 10 and 30 pm, respectively. The new respirable sampling convention is a compromise between the older American ACGIH convention,12 and European convention, originally defined by the British Medical Research Council (BMRC) and given international recognition at The Second Pneumoconiosis Conference in Johannesburg in 1959.1328 Analyst, January 1994, VoE.119 The sampling conventions were not formulated with the object of enabling sampling of doses for specific individuals. The statistical nature of the definition implies that the sampling conventions are to be used for measuring the quality of the air that a worker inhales, rather than the dose a specific worker has received. Although there is wide variation in individual deposition doses, the air quality (or contamination as measured according to the sampling convention) is a unique property. Therefore, the wide human dose variation may not be used as an argument for allowing a wide variation among samplers.However, it might be argued, that any sampler that only poorly matches the sampling convention, most probably corresponds to the deposition of at least one worker in the world. If a wide variation among sampler efficiencies were allowed, a deplorable situation can occur where the vested interest of management, workers, or factory inspectors could determine the choice of sampler. If a specific individual’s dose is to be measured, then that individual’s deposition must first be determined under hisher working conditions. Aerosol Sampler Performance To evaluate a sampler’s performance it must be compared with either another sampler or a sampling convention, in order to ensure that different samplers using different inlets and different means of size-selection measure similar aerosol concentrations.Some samplers are in themselves implied standards. This is often the case with those samplers devel- oped in the 1960s and 70s and presently used for sampling total and respirable dust. Total dust, for example, is measured world-wide, but many countries have their own definition of it, i.e., their national version of a total dust sampling head. In US Coal Mines a specific cyclone is required for sampling respirable coal dust, i.e., the 10 mm nylon cyclone.14 In British coal mines, coal dust is measured in the return air with a stationary horizontal elutriator, which in calm air perfectly follows the BMRC sampling convention for respirable dust. 15 The latter sampling convention was itself designed as the theoretical penetration of a horizontal elutriator.Presently, only cyclones used to sample respirable dust (excluding coal mines), and samplers for inhalable dust used in some countries in Europe (e.g., United Kingdom16) can be said to be designed to follow a specific sampling convention. However, because a virtual one-design monopoly exists on which sampler to use in any particular country, the sampler commonly used may be viewed as a standard in itself. The aim of the CEN standards on aerosol sampling is to ensure that different samplers may be used, provided they give similar results. This is only 1.0 I 1 o-2 I 01 +- -...__ 1 1 10 100 Particle aerodynamic diametedpm Fig. 1 CEN-ISO-ACGIH sampling conventions for: A, inhalable; B, thoracic; and C respirable fractions possible if the samplers follow a pre-determined sampling convention, rather than all being standards in themselves.To elevate any of the national samplers presently used in Europe to a European standard was deemed not to be politically possible, and furthermore was contrary to the General Performance Requirements of CEN.17 In order to better follow the new international sampling conventions, national (standard-in-itself) samplers may have to be optimized if they deviate too much from the sampling convention. CEN’s approach stimulates the development of new and hopefully better, samplers, as opposed to the present system. In principle, three different methods exist to establish whether a new sampler follows a sampling convention.The first, and simplest, method is possible only if a reference sampler that perfectly follows the sampling conven- tion exists. In such a case the mass concentrations sampled simultaneously both with the new and the reference sampler may be compared. Such a comparison must be repeated for several different aerosols with different size distributions. A possible requirement is that for each size distribution both the bias and variance of the new sampler is within some specified limits. References 18 and 19 describe tests based on some of these principles. In the second method the sampling efficiency of the new sampler is compared with that of the prescribed sampling convention. Usually the efficiency data for the new sampler are plotted against those of the sampling convention to construct a sampling efficiency curve.A possible requirement here is to establish tolerance bands on how much the sampling efficiency may deviate from the convention, together with some requirements on the particle size corresponding to 50% efficiency and the slope of the new sampler’s efficiency curve .20,21 In the third method the efficiency data for the new sampler are also used to construct a sampling efficiency curve. However, in this case the data are used to compute the sampled mass fraction of the new sampler for a set of log- normal size distributions, and then compare these computed data with a similar set based on an ideal hypothetical sampler that perfectly follows the sampling convention. A possible requirement in this case is that some combination of bias and variance, somehow determined over the whole set of size distributions, should be below a specified value.22 All three methods have their pros and cons.The first method is easy and cheap to use, but requires several different test aerosols. It is only possible when a reference instrument exists, as for example the horizontal elutriator for the BMRC convention in calm air. The second method gives more information, but the relationship between the tolerance bands and measured concentrations is not apparent.15.23 The third method gives results that are more related to the needs of the end users. However, the validity of the calculations of sampled concen- trations have, at least in one case, been questioned.24 In order to be able to test and evaluate a sampler the test configuration has to be determined.The ideal configuration is one which tests a sampler for all possible situations likely to occur in field sampling. It is, however, neither possible to anticipate all possible situations, nor would it be economically feasible. An example of a field sampling situation is shown in Fig. 2. Both the wind velocity and the aerosol concentrations far from the worker are low. The dust source, possibly with simultaneous emission of air jets, is local and is thus related to the worker’s actions. There is, therefore, a preferred direction relative to the source. Hopefully a local exhaust is also present. In order to test a sampler an ideal (simplified) model that emulates only the most significant aspects of field sampling, must therefore be designed.The concept of inhalable dust is based on such a simplified ideal model. The inhalability is determined in a wind tunnel using a rotatingAnalyst, January 1994, Vol. 119 29 life-sized breathing mannequin and homogeneously dis- tributed particles released remotely upstream from the mannequin and thus in a steady-state with respect to the external air flow. Fig. 3 shows a schematic diagram of this set-up. In this ideal model no objects disturb the air flow, and there is no local emission of particles or air jets. For this ideal situation it is possible to design experiments to determine how well a sampler emulates a sampling convention. Workplace reality must therefore, not be confused with the ideal test configuration.In workplaces that differ significantly from the ideal model one cannot assume that the measured inhalable fraction approximates what the worker inhaled. This is exemplified when the exposure is extremely unidirectional, or the particles are released into the air in such a way that they are not in a steady-state relative to the external air flow, when sampled or aspirated by the worker. CEN Sampler Performance Test Procedure Using a sampler that emulates a sampling convention, we need to be sure that the measured concentrations when used for workplace sampling are correct within acceptable tolerances. In order to determine if a sampler is good enough it must be evaluated. Preferably this should be done in a simple, cheap, quick, generally applicable, and easily performed experiment that for a standardized test aerosol gives results that are valid for all aerosols encountered in the work environment.Such a test is not possible to design, and the performance test that is proposed by the CEN working group is concerned mainly with the fact that the results obtained should be valid in most work environments. This paper presents a broad outline of the draft performance test standard.25.26 Readers interested in the full text may contact the working group’s convenor. The object of the working group was that the test procedure should follow the Technical Committee’s General Performance Require- ments.17 However, because of the special nature of aerosol sampling, some deviations were necessary and these will be presented explicitly later in the text. The CEN working group on particulate matter has pro- posed two different test procedures to evaluate the perfor- I IY Fig.2 Model of a workplace with worker close to emissions of particles and air jets. A local exhaust is used. Far from the source, both the wind speed and aerosol concentrations are low Fig. 3 Ideal model of a workplace used for determining inhalability in wind tunnels. All particles are generated far from the worker, where both the aerosol concentration (C,) and wind velocity (w) are constant. No large objects close to worker, and therefore all local air movement is caused by wind divergence around the worker mance of aerosol samplers. The first is a laboratory evaluation of personal or static reference samplers.This test is only intended for samplers with aerodynamic separation of par- ticles and subsequent collection of the sampled particles on a substrate, e.g., a filter. The classification obtained as a result of the test will be a property of the sampler. The second test is a field comparison of any type of sampler, e.g., a light- scattering instrument, with a reference sampler. In this case the classification will be specific to the test situation and will not be valid under other circumstances. Reference Sampler Clussifcation The laboratory evaluation of sampler performance is a comprehensive test that measures the sampling efficiency as a function of particle size and other influencing variables, such as wind speed. The test should preferably be performed on used commercial samples, not prototypes.The test is com- prised of several stages. The first stage is a critical review of the physics of the sampling process, including all the steps in the process by which the instrument aspirates, transports, separates and collects particles. In the laboratory experiment all influencing variables considered to be of importance for the sampling process are investigated. From the measured effi- ciency data, sampling efficiency curves are determined. There is no specific requirement on which type of curve should be used to model the sampling efficiency. The only requirement is that the efficiency curve must have a shape consistent with the physics of the sampling process and not have unrealistic asymptotics outside the range of the data points.Using the efficiency curves the mass collected by the sampler is calculated for a set of log-normally distributed aerosols. These masses are compared to what would have been collected by an ideal hypothetical sampler perfectly following the sampling convention. Both the sampler bias and variance are calcu- lated. Finally the sampler is classified by combining the bias and variance. CEN assumes in its General Performance Requirements17 that the performance test is specific for each substance, that is, the same sample is used for the determination of both sampling and analytical errors, expressed as the total overall uncertainty. This implies that one test should be performed for each substance on the threshold limit value list, for each of its solifliquid occurrences, for each sampling method and for each analytical method.It is not feasible to perform such a long list of performance tests. In addition, monodisperse test particles, which are necessary for a test against a sampling convention, cannot be generated from all kinds of substances. Therefore, the laboratory evaluation of a reference sampler using only one type of aerosol which may not even have a threshold limit value is the first departure from the scheme laid out by the CEN General Performance Requirements. Critical Review of Sampling Process The purpose of the critical review is to identify instrumental or instrumentaknvironmental interaction factors that influence the sampler performance relative to the sampling convention.The critical review may analyse the following steps of the sampling process: sampler preparation (e. g., cleaning); collec- tion and substrate preparation (e.g. , selection and application of impaction media); airflow adjustment; aerosol aspiration; internal aerosol separation; aerosol collection; transport of collected material to analytical laboratory; and chemical analysis. The critical review will determine the design of the test to quantify the effects of the most important factors. The draft standard lists typical factors that may be important (see Table 1). It also specifies some potential problems, as for example particle de-agglomeration and particles flying into30 Analyst, January 1994, Vol. 119 the inlet under their own momentum, rather than being aspirated into the sampler by air velocities caused by a combination of external air movement and sampler airflow.For the factors most likely to have strong influences, the draft standard specifies the ranges over which the influencing variables should be tested. A summary of these variables is presented in Table 2. Laboratory Experiment Based on the critical review an experimental plan is designed. The draft standard provides some efficient statistical designs that allow the effects of particle size, one environmental factor (e.g., wind speed), sampler specimen variability and personal sampler position to be determined simultaneously. Instruments that are to be used as personal samplers, must be tested as such, i.e., mounted on a lifesize mannequin in a wind tunnel.The internal penetration of samplers for the respirable and thoracic fractions may be tested separately in a calm air chamber or by introducing the aerosol directly into the sampler inlet, if the aspiration efficiency of a sampler in a wind tunnel and in calm air are both known. The flow dependence of the sampler must be known, or experimentally determined, for subsequent analysis. The draft standard does not specify exactly how the aerosol experiments are to be carried out. Instead a great deal is left to the discretion of the testing laboratory, but with requirements on the allowed experimental sampling and analytical errors. The laboratory tests may be performed with either mono- or poly-disperse aerosols. The choice of test aerosol depends on the availability of suitable methods for measuring particle aerodynamic size with unique and monotonic calibration functions.Correction factors for particle density and shape Table 1 Factors influencing sampler performance Environmental Particle size Wind speed and direction Aerosol composition Aerosol concentration Aerosol charge Temperature, pressure, humidity Vibration, orientation Instrumental Specimen variability How variations Surface treatments Sampler position Sampled aerosol mass Sample transportation Electromagnetic susceptibility may be used. The test aerosol concentration and size distribution should be spatially homogeneous. The allowed analytical errors in determining the sampling efficiency must be less than 1-2%. The ambient aerosol concentration should be sampled with thin-walled sharp-edged probes, operating iso-kinetically in a wind tunnel.The experimental uncertain- ties should be evaluated. Several aspects of the wind tunnel test are still provisional and will be studied over the next few years. Among these answers are required to the following questions: Should the mannequin be breathing? May the mannequin be replaced by a simple wood board? What is the effect of turbulence? Data Treatment How the experimental sampling efficiency data is to be treated is extensively described in the draft standard. Only a broad outline will be presented here. From the measured sampling efficiency data, an average sampling efficiency curve, Eff, (dae), is drawn as a function of particle aerodynamic diameter, d,,, for each environmental factor tested.This curve is then used to calculate the sampled mass fraction for a set of log-normal aerosol size distributions. For all three sampling conventions the set is based on the following size distribution parameters: aerodynamic mass median diameter (MMAD) in the range 1-25 pm in steps of 1 pm, geometric standard deviation (og) in the range 1.75-3.50 in steps of 0.25. Size distributions for which the fraction is less than 5% of the total ambient are excluded (this occurs only with the respir- able fraction for narrow size distributions with large MMADs). The average sampled mass fraction, F,, is calcu- lated by 00 Fe (MMAD, og) = J Effe(dae) A(dae I MMAD, o g ) ddae (1) 0 where A(d,, I MMAD, og) is a log-normal aerosol size dis- tribution with parameters MMAD and og.The mass fraction that would have been sampled by an ideal hypothetical sampler perfectly following the sampling conven- tion is calculated using the same equation, but exchanging Eff,(d,,) for the sampling convention curve. From these two sets of mass fraction data, the bias of the sampler is calculated as the percentage difference between the mass fractions sampled by the sampler and the sampling convention. It is a function of log-normal aerosol size distributions (with parameters MMAD and og) and environmental factors. For Table 2 Range and number of influencing variables to be tested Variable Particle size Wind speed Wind direction Range Inhalable 1-100 pm Thoracic 0.1-35 pm Respirable 0.1-15 pm Indoor workplaces 0-1.5 m s- Outdoor workplaces 0-4 m s- Omnidirectional average Aerosol composition Sampled mass Aerosol charge Sampler specimen variability Flow rate variations Particle collection surfaces Position of use (personal samplers) Phase: solid andor liquid; particles of known shape Up to mass corresponding to: maximum concentration x design flow rate X sampling time Charged or neutralized aerosol; conducting or insulating sampler Test group to be as large as possible and always at least three specimens Design flow rate f5% Choice of collection materials (e.g., filters and foams) and details of any surface treatments to be stated Within area stated in the user instructions Number of values 9-12 3 3 Continuous revolution or 24 Choose suitable materials values stepwise Choose and document 3 1-531 Analyst, January 1994, Vol.I1 9 each tested influencing variable, a bias map is drawn showing the sampler bias relative to the sampling convention as a function of aerosol size distribution parameters. An example is shown in Fig. 4. In the diagram the area marked with horizontal lines represents a bias between f O and + 10%. The thick solid lines represent the region in which the performance will be classified. If the average bias is similar for aerosol size distributions of interest and all tested relevant influencing variables, the bias may be reduced by multiplying all concentrations with a correction factor. A correction factor that significantly decreases the bias is allowed and shall then always be applied when the sampler is used. Using all the experimental efficiency data the uncertainty in the sampler bias and the variance due to differences among sampler specimens is calculated. The total sampler variance has two components, the specimen variability and the flow setting errors.The draft standard presents two performance indexes, the overall uncertainty as defined by the CEN General Perfor- mance Requirements,l7 and the sampler accuracy (defined in the draft standard). The overall uncertainty is calculated as the sum of the absolute bias and twice the relative standard deviation, incorporating any error from a subsequent chem- ical analysis (which therefore has to be added to the total sampler variance). The sampler accuracy is defined for the sampler itself, excluding any subsequent chemical or gravi- metric analysis.It is the maximum error relative to the true value that 90% of all samples taken with the sampler will have, with 90% confidence (incorporating the uncertainties in measured bias and total sampler variance). The CEN working group prefers the accuracy criteria for sampler classification because it classifies the sampler itself, even though it is at variance with the CEN General Performance Requirements. Similar to bias maps, accuracy maps should be drawn for each tested relevant influencing variable, presenting the accuracy as a function of the aerosol size distribution parameters. See Fig. 5 for an example of an accuracy map obtained for one value of a tested influencing variable. The thick solid lines represent the region in which the performance is classified.ClassiJicaton The draft standard suggests that a sampler is deemed to be satisfactory for any environment where its accuracy for the calculated sampled mass fraction is within or equal to +30%. This figure of 30% is regulated in the CEN General Performance Requirements for samples taken in the concen- tration range from one half to twice the limit value.17 It is believed that there would not be many samplers having an accuracy better than 30% for all size distributions of interest and all tested environmental factors. Instead of rejecting those samplers with an accuracy >f30% which is obtained in some of these cases, a classification scheme is designed so that a sampler is assigned to a higher class the wider the range of conditions for which it has an accuracy S230%.This is the third major deviation from the CEN General Performance Requirements. The accuracy is calculated for the set of size distributions defined above, and in the classification scheme the individual size distributions used are termed classification points. Three classes were designed, labelled 1,2 and 3. The draft classification scheme has been arbitrarily decided and will be reviewed in light of the experience gained from the pan- European test of inhalable samplers. Samplers failing to meet any of the class requirements and untested samplers will be termed unclassified. These shall not be used for health-related aerosol sampling in workplace air. Class I sampler The average sampling efficiency for this sampler at each tested particle size should be in the range 8&125% of the ideal efficiency given by the sampling convention, for particle aerodynamic diameters larger than 1 pm and where the value of the sampling convention is greater than 10% it meets the required accuracy for 100% of the classification points, for all tested values of relevant influencing variables.and Class 2 sampler This sampler meets the required accuracy for 270% of the classification points, for all tested values of relevant influenc- ing variables it meets the required accuracy for 100% of the classification points, for only two out of three tested values of relevant influencing variables. or Class 3 sampler This meets the required accuracy for 230% of the classifica- tion points, for all tested values of relevant influencing variables it meets the required accuracy for 100% of the classification or Fig.4 Example of bias map, showing contours of equal bias (%) in Fig. 5 Example of accuracy map, showing contours of equal the thoracic fraction of a tested sampler, relative to the sampling accuracy (%) in the thoracic fraction of a tested sampler, relative to convention for one tested influencing variable, for log-normal aerosol the sampling convention for one tested influencing variable, for size distributions, as a function of MMAD and up log-normal aerosol size distributions, as a function of MMAD and ug32 Analyst, January 1994, Vol. I19 points, for only one out of three tested values of relevant influencing variables. In the case of a thoracic sampler as shown in Fig.5, the accuracy is less than 30% in all classification points for this tested relevant influencing variable. Field Sampler Comparison The draft standard presents a method for field comparisons between any type of aerosol sampler (e.g., a light-scattering instrument) and a reference sampler having an accuracy better than or equal to f30% under the circumstances of the field test. The purpose of the field test is to obtain a correction function relating the tested sampler concentrations to those of the reference sampler. If an acceptable correction function is obtained, the tested sampler is placed in class 4, otherwise it remains unclassified. A class 4 award following a field comparison is only valid under the exact conditions under which the test was carried out.That is, it depends on the properties of the aerosol sampled, and on the environmental conditions of the test. It cannot be assumed that the correction function may apply to other circumstances. At the test a personal sampler should be compared with a personal reference sampler, and a static sampler compared with a static reference sampler. The number of measurement pairs should be as large as possible and never less than 10. The measurements should cover the range of aerosol properties, including concentration and environmental conditions occurring at the sampling sites. To check the stability of the correction function two separate comparison exercises should be carried out, each consisting of at least 10 measurement pairs. The correction function between the tested sampler and the reference sampler concentrations may be calculated by any statistical procedure. The data and the curve should be plotted onto a graph, and the residuals of the curve should be examined.The tested sampler is classified according to whether it passes some preliminary statistical tests which will later be reviewed. The first requirement is that the average relative residual bias differs insignificantly from zero. The second requirement is that the average relative residual biases from the two comparison exercises must not differ significantly. The third requirement is that no more than 10% of the absolute residual biases exceed half of the average concentration. Sampling Pump Requirements Another CEN working group has drafted a standard on personal sampling pumps, both for aerosol and/or gas-vapour sampling.27 This standard is applicable to any personal sampling pump with a flow rate in the range 5 ml min-* to 5 I min-1.The standard gives both the performance require- ments and the procedure to test the pumps. Table 3 lists the performance requirements. Pumps which have passed the test should be specially labelled. The performance of a personal sampling pump is evaluated in a laboratory test. The test of the influence of back pressure is made at the minimum and maximum nominal flow rates claimed by the manufacturer. The test of the pump's capability to withstand long operating times is made at two flow rates, 2 1 min-1 and maximum nominal flow rate, with a flow resistance of 1.6 kPa (corresponding to an unused 37 mm cellulose acetate filter of 0.8 pm pore size).For the test of the influence of temperature, and orientation, a flow rate of 2 1 min-1 and a flow resistance of 0.5 kPa (corresponding to an unused 37 mm cellulose acetate filter of 8 pm pore size) is used. In the test for mechanical strength, a flow rate of 2 1 min-1 and a flow resistance of 3.2 kPa is used. The pulsation test is carried out at a flow rate of 2 I min-* using a flow resistance of 0.75 kPa. The test does not require flow resistances as large as the pressure drop at approximately 2 1 min-1 over 25 mm cellulose acetate filters with 0.8 pm pore size (=4 kPa) or 25 mm polycarbonate filters with 0.4 pm pore size (=5 kPa). The problem of accurate airflow measurements is not addressed by this standard.European Test of Samplers for Inhalable Dust As mentioned earlier, the aerosol sampler test protocol will be used in a European test (which began in spring 1993) of personal samplers used for sampling inhalabk dust or total dust.28 This sampler test will also be a test of several assumptions behind the test procedure, and hopefully, as a result future tests of samplers for inhalable dust may be carried out according to a more simple procedure. The following samplers are included in the test: The SKC IOM personal sampler for inhalable dust, the British seven- hole sampler, the French Arelco CIP-10 with the internal respirable separator removed, the German Strohlein GSP Table 3 Performance requirements for personal sampling pumps for aerosol sampling Features Mass Mechanical safety Electromagnetic compatibility Operating time Flow-rate stability due to back pressure Flow-rate stability over operating time Emergency indicator/ shut-down Temperature Mechanical strength dependence Flow-rate pulsation Orientation Explosion resistance Clock accuracy Instructions for use Labelling Charger Holder to attach pump to wearer Malfunction indicator or automatic Fuse or electrical current restrictor in case Inadvertent flow adjustment made difficult Including batteries and integral holders Avoid sharp corners or uncomfortable parts Meet requirements in EN 50 081-1 and At 2 1 min-1 and maximum nominal Flow rate within +5% if pressure varies emergency stop of short circuit S1.2 kg EN 50 082-1 capacity, at least 2 hand preferably 8 h 10 times, e.g., for a pump with nominal capacity of 2 1 min-1 the pressure range is 0.34.0 kPa Within k5%0 at 20 and 5 "C If flow is reduced by 50% for 1 min, indicator must activate and remain until reset, or pump must stop and not start by itself In range 540 "C flow rate may deviate G +5% from value set at 20 "C No general pump function impaired by shock treatment.The flow rate may deviate <+5% S10% For pump tilted go", flow rate must deviate If claimed by manufacturer, according to For pumps with internal clock, after 8 h The minimum requirement for the <?5%0 EN 50 014 use, deviation <1 min instruction manual is listed in the draft standard manufacturer, type designation, serial number, the European standard, and whether it may be used in explosive areas battery type, and meets requirements of The pump shall be labelled with Designated by manufacturer, tuned to EN 60 335-133 Analyst, January 1994, Vol.I1 9 sampler for inhalable dust, the Italian Lavoro e Ambiente PERSPEC, the Dutch PAS-6 sampler, and the 37 mm cassette in open and closed face versions. The laboratory experiments use a breathing mannequin in a wind tunnel. The test aerosol are nine monodisperse particle sizes, made of fused aluminium oxide and ranging from 5 to 90 p,m. The samplers are tested in three positions on the front of the mannequin. The wind speeds tested are 0.3, 1.5 and 4 m s-1. The draft standards described are the result of the collective work of the CEN working groups. 1 2 3 4 5 6 7 8 9 10 11 12 13 References Phalen, R.F., in Particle Size-Selective Sampling in the Workplace, Report of the ACGIH Technical Committee on Air Sampling Procedures, ACGIH, Cincinnati, USA, 1985. Nordiska Expertgruppen for Gransvardesdokumentation 77, ‘Troestgv’ (Nordic Expert Group Basis for an Occupational Health Standard 77, Wood Dust), Arbete och Halsa, 1987: 36. Hatch, T., and Gross, P., Pulmonary Deposition and Retention of Inhaled Particles, Academic Press, New York, 1964. Chan, T. L., and Lippmann, M., Am. Ind. Hyg. Assoc. J., 1980, 41, 399. Heyder, J., Gebhard, J., Rudolph, G., Schiller, C. F., and Stahlhofen, W., J. Aerosol Sci., 1986, 17, 811. Miller, F. J., Martonen, T. B., Menache, M. G., Graham, R. C., Spektor, D. M., and Lippmann, M., in Inhaled Particles V I , eds.Dodgson, J . , McCall, R. I., Bailey, M. R., and Fisher, D. R., Pergamon Press, Oxford, 1988, pp. 3-10. Vincent, J. H., Mark, D., Miller, B. G., Armbruster, L., and Ogden, T. L., J. Aerosol Sci., 1990, 21 (4), 577. ComitC EuropCen de Normalisation, EN481 Workplace Atmos- pheres. Size Fraction Definitions for Measurement of Airborne Particles, Brussels, Belgium. International Organisation for Standardisation, Technical Com- mittee 146, DIS 7708 Air Quality-Particle Size Definitions for Health-related Sampling, Geneva, Switzerland. American Conference of Governmental Industrial Hygienists, 1992-1993 Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices, ACGIH, Cincinnati, OH, 1992. Soderholm, S. C., Ann. Occup.Hyg., 1989, 33 (3), 301. Committee on Threshold Limit Values, Threshold Limit Values of Airborne Contaminants for 1968, American Conference of Governmental Industrial Hygienists, Cincinnati, OH, 1968. Orenstein, A. J . , Proc. Pneumoconiosis Conference, Johannes- burg 1959, J & A Churchill, London, 1960. 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 30 Code of US Federal Regulation, part 74, 1982. LidCn, G., and Kenny, L. C., Ann. Occup. Hyg., 1991,35 (5), 485. Health and Safety Executive, MDHSl4 General Methods for Gravimetric Determination of Respirable and Total Inhalable Dust, London. ComitC EuropCen de Normalisation, prEN482 General Require- ments for the Performance of Procedures for Workplace Measurements, Brussels, Belgium. Tomb, T. F., Treaftis, H. N., Mundell, R. L., and Parobeck, P. S., Comparison of Respirable Dust Concentrations Measured with MRE and Modified Personal Gravimetric Sampling Equip- ment, Report RI7772, US Bureau of Mines, Pittsburg, USA, 1973. Caplan, K. J., Doemeny, L. J., and Sorenson, S. D., Am. Ind. Hyg. Assoc. J., 1977,38 (4), 162. Luftbeschaffenheit am Arbeitplatz- Einatembarer und alveolen- gangiger Staub, (Workplace Air Quality-Inhalable and Respir- able Dust), NLuft/AA 11 AK No. 8-88, Deutsches Institute fur Normung e.v., Berlin, 1988. McCawley , M. A., in Particle Size-Selective Sampling in the Workplace, Report of the ACGIH Technical Committee on Air Sampling Procedures, ACGIH, Cincinnati, OH, 1985. Bowman, J. D., Bartley, D. L., Breuer, G. M., Doemeny, L. J., and Murdock, D. J., Accuracy Criteria Recommended for the Certification of Gravimetric Coal Mine Dust Samplers, National Institute of Occupational Safety and Health, Cincinnati, OH, 1984. Bartley, D. L., Doemeny, L. J., Am. Ind. Hyg. Assoc. J . , 1986, 47 (8), 443 and A498. Treaftis, H. N., Gero, A. J., Kacsmar, P. M., and Tomb, T. F., Am. Ind. Hyg. Assoc. J., 1984, 45, 826. CEN/TC137/WG3/N125 Workplace Atrnospheres-Assessment of Performance of Instruments for Measurement of Airborne Particles (draft 5). Available from the CEN working group convenor, Ogden, T., Health and Safety Executive, London. Kenny, L. C., 1. Aerosol Sci., 1992, 23 (7), 773. CENITC137lN90 Workplace Atmospheres-Pumps for Per- sonal Sampling of Chemical Agents. Requirements and Test Methods. Available from the CEN working group convenor, Siekmann, H., Berufsgenossenschaftliches Institut fur Arbeits- sicherheit, Germany. Measurement and Testing Programme of the Council of Ministers of the European Community, Contract CT920047, Pilot Study of CEN Protocols for the Performance Testing of Workplace Aerosol Sampling Instruments. Paper 3103207H Received June 4, 1993 Accepted September 9, 1993

ISSN:0003-2654    

DOI:10.1039/AN9941900027

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Analyst, January 1994, Vol. 119 35 Direct-reading Instruments for Aerosols*J A Review P. A. Baron US Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, 4676 Columbia Parkway, Cincinnati, OH 45226, USA Direct-reading instruments for aerosols have not had the popularity within the industrial hygiene community that similar instruments for gases and vapours have enjoyed. There are several reasons for this: aerosols have complex properties that are difficult to characterize with a single measurement, commercial instruments often do not provide an accurate measure of a useful aerosol property and aerosol instruments are relatively expensive for industrial hygiene use. A variety of instruments are commercially available and are briefly reviewed. Two general classes of instruments used for industrial hygiene measurements are covered: field instruments and research instruments.The International Symposium on Air Sampling Instrument Performance held in Research Triangle Park, NC, USA, in October, 1991 included a workshop on direct-reading aerosol instruments that produced several recommendations to advance the state of the art. The two primary recommendations approved by the symposium attendees were to develop voluntary consensus standards for aerosol mass measuring instruments and optical particle counters and to develop an accurate, portable, direct-reading aerosol mass monitor. Some progress is being made on the latter recommendation through a project supported by the US Bureau of Mines.Other instruments have found specific application in industrial hygiene measurements. A miniaturized condensation nucleus counter is being used to estimate fit factors for respirators. A fibre monitor is used for monitoring asbestos, especially in asbestos abatement operations. Optical particle counters are used for low-concentration aerosols, especially in clean rooms. Aerosol research instruments are being used to evaluate and improve field instrumentation, such as respirable, thoracic and inhalable samplers and cascade impactors. Several such direct-reading instruments are now commercially available that can rapidly measure aerosol concentration and size distribution. These instruments can also be used to make field measurements.Accurate aerosol sampling is often difficult in uncontrolled atmospheres; many direct-reading instrument manufacturers have paid little attention to inlet characteristics of their instruments. Errors due to sampling and internal instrument losses can be large. Keywords: Direct-reading instruments; aerosols Introduction There are many aerosol contaminants in workplace environ- ments that can cause detrimental health effects. Monitoring techniques for estimating aerosol contaminant concentrations frequently require that a sample be taken and sent to a * Presented at the Conference on Modern Principles of Workplace Air Monitoring: Pumped and Diffusive Sampling for Contaminants, Geilo, Norway, February 15-18, 1993. 1 Mention of a product or company name does not constitute endorsement by the Centers for Disease Control and Prevention. laboratory for analysis.However, it is often desirable to obtain concentration information rapidly in order to estimate hazard levels, to evaluate control systems or to provide feedback so that exposed persons can modify behaviour and thus reduce health risk. These instruments can also allow the laboratory-analysed samples to be taken in an efficient manner, e.g., in the most appropriate location and for an optimum duration. Direct-reading instruments can fulfil these needs and portable instruments of this type are often the most convenient to use. Some areas related to direct-reading aerosol instruments are surveyed. Several commercially available portable instru- ments are discussed briefly, as these are generally of most interest to industrial hygienists, and some directions of current research will be indicated.A discussion of some aerosol research instruments is included. These discussions do not attempt to be comprehensive, as there are publications available on measurement techniques. 1 7 2 A recent workshop on air sampling instruments, held at a symposium sponsored by the American Conference of Governmental Industrial Hygienists (ACGIH) ,3 produced a set of recommendations regarding direct-reading aerosol instruments. These recommendations will be summarized. The full set of recommendations from all the workshops at this symposium has been published. The last area of interest is peripheral to direct-reading instruments, but can significantly affect measurement accu- racy.Sampling efficiency, internal instrument losses, and instrument calibration are all important factors in this regard. Direct-reading Instrumentation Different types of instruments are used for making workplace measurements of aerosols. These instruments are used to obtain specific information about the aerosols. The most common type of measurement is to determine the mass concentration of the aerosol. Many regulatory exposure limits are based on mass concentration, as the health effect due to exposure is proportional to aerosol mass. Within this cate- gory, several types of mass measurements are made, including those for respirable mass (representing particles that reach the alveolar region) , thoracic mass (particles reaching the thoracic region) and inhalable (or total) mass .4 For direct-reading instruments, a pre-classifier is often used to remove non-respirable or non-thoracic particles, so that the instrument only detects the desired fraction.Respirable mass measurements are perhaps the most common type of aerosol measurement because insoluble particles reaching the alveolar region of the respiratory tract are removed from the lung relatively slowly and have the greatest time to induce adverse health effects. Many of the instruments that purport to measure mass are unsatisfactory because of a lack of accuracy, portability or ease of use. In addition, the specific requirements of some applications may preclude the use of certain collection or detection techniques, e.g., explosive36 Analyst, January 1994, Vol.11 9 atmospheres in coal mines necessitate the use of spark-free (intrinsically safe) instruments. For certain types of measurements, the number concentra- tion of an aerosol is useful. One such measurement is the leakage rate of respirators. At low aerosol concentrations, measurement of the number concentration of particles inside and outside the respirator is a useful way of determining penetration of an aerosol through and around the respirator. Number concentration is also a useful measure of low- concentration aerosols, such as in clean rooms. The behaviour of aerosols often measured in the workplace is largely governed by the particle aerodynamic diameter. For instance, the settling and impaction of particles within the respiratory system can be explained using the aerodynamic diameter.Measurement of the aerosol aerodynamic diameter size distribution is therefore useful in understanding aerosol behaviour. With the variety of chemicals to which workers can be exposed, it is often useful to determine specific components of an aerosol. Thus, instruments that measure only particles with a certain chemical, element or shape can be useful. There have been several attempts to make field analytical instruments specific for certain elements, e.g., lead5 and other elements,6 but none of these are portable instruments. There are several particle properties that are important in different applications. In monitoring for the control of detrimental health effects, the toxicity of individual particles is clearly important. Health effects from aerosol exposure often depend directly on particle chemistry, although in certain instances they may depend on particle size (e.g., respirable) and shape (e.g., asbestos fibres).Unfortunately, there are very few direct-reading aerosol instruments capable of provid- ing qualitative analysis. It is difficult enough to perform such analyses, especially for multiple analytes, on collected sam- ples in a laboratory. However, for some specific chemicals, the development of such instruments may be warranted. Light-scattering Instruments Photometers or nephelometers are perhaps the most com- monly used direct-reading aerosol instruments. These have been commercially available for over 20 years and are available in a variety of configurations.7 The detection mechanism is depicted in Fig.1. A light source illuminates the detection volume through which the aerosol passes. Light scattered from the particles is collected and detected. The angle of light detection relative to the direction of illumination will determine the relative detection efficiency for small and large particles. Large particles are detected more efficiently at small scattering angles, while sub-micrometre particles scatter more uniformly in all directions. Many of the particles of interest are in the Mie scattering range. For simple geometric shapes such as spheres and rods, the Mie scattering pattern can be predicted theoretically .8 However, for most dust particles, the complex and varied shapes do not warrant even attempting the difficulties of predicting their scattering patterns.Each instrument uses a specific range of scattering angles. In addition to size, particle refractive index and shape also play an important role in the direction and intensity of scattering. Particles smaller than 0.3 pm in diameter are detected very inefficiently, if at all, as scattering decreases as the fourth power of particle diameter in this size range. Large particles scatter light proportionally to their cross-sectional area. Maximum detection efficiency generally occurs in the 0.5-2 pm particle diameter range. The shape of the particle volume (or mass) response curve is indicated in Fig. 2. The fall-off in the 1-10 pm range is approximately similar to the respirable dust curve,9 so these instruments are often used as indicators of respirable dust concentration.Of course, the calibration of the instrument for this purpose is important, because the calibration will change with particle size distribution, refractive index and shape. The instrument measures the light scattered from all particles present in the detection volume and, therefore, is fairly sensitive to low concentrations of aerosol. The aerosol can be measured on a continuous basis, and the components of the detection system are relatively common and inexpensive. The measured concentration is independent of the flow rate through the sensing volume. Hence the instrument can be used at a variety of flow rates; some instruments use ‘passive sampling’, i.e., the natural convection in the environment, to push the aerosol through the sensor. Hence the photometer is useful as a relatively inexpensive, approximate, real-time indicator of aerosol concentration.Improvements to photometers are not likely to make these instruments more useful than current instruments for typically desired measurements of workplace aerosols, such as mass, respirable mass or other particle properties. The intrinsic response to scattered light depends in a complex way on particle shape, refractive index and size. For instance, changes in particle size distribution or chemistry can readily cause changes of 50% or more in the detected light scattering signal for the same particle mass. These instruments, because of their relative simplicity, can be made small and portable.Hence they are convenient for sniffers in providing approximate indications of aerosol concentration. In this vein, they can be used for locating aerosol sources, evaluating respirators, evaluating control systems or determining approximate concentrations of respir- able dust. Optical particle counters (OPCs) are very similar to photometers in principle (Fig. l), except that the detection volume is much smaller and the aerosol flow rate through the detection volume is carefully controlled so that particle Rayleigh Geometric regime regime optics Complex Fig. 1 Optical detector for aerosol particles 0.01 0.01 0.1 1 10 100 1000 Particle diametertpm Fig. 2 diameter Light scattering per mass of aerosol as a function of particleAnalyst, January 1994, Vol. 119 37 concentration can be determined.' The signal from each particle generally increases with increasing particle size, so that some size distribution information can be obtained from these instruments.These instruments may be used for low-concentration measurements, since single particles are counted. They have been used for clean room measurements. OPCs are generally more sophisticated than photometers, requiring better control of airflow, including a sheath air system and more complex electronics. A great deal of literature and many commercial OPC instruments exist, indicating a mature technology. As with photometers, it is unlikely that there will be any real breakthroughs in improve- ments for specific measurements. However, the light-scatter- ing detection principle is very sensitive and well understood, so that it is possible to combine the OPC principle with other detection or particle separation mechanisms to produce an instrument responsive to some desired particle property.Examples of such an approach include aerodynamic particle sizers, which use nozzle acceleration, and fibrous aerosol monitors, which use electrostatic alignment. These instru- ments are discussed further below. Detection of light transmission is another approach to aerosol particle detection. However, the sensitivity is not as high as for light scattering and this approach is used for high-concentration aerosols, such as in smoke stacks, or in environmental measurements, where long measurement path lengths can be used.Piezoelectric Microbalance The piezoelectric balance consists of a piezoelectric crystal on which particles are deposited by electrostatic precipitation or impaction (Fig. 3).1* The collected mass is measured from the change in resonant frequency of the crystal. Because the particles must couple to the crystal surface, the surface must be frequently cleaned. Some particles may not couple well to the surface. One end of a chain or fibre may attach to the surface while the other end moves freely and does not couple to the crystal surface; large particles may not adhere suffi- ciently to the crystal surface to change the resonant frequency, and some collected liquids may flow to the nodes of vibration, also resulting in reduced sensitivity. A recent evaluation of a piezobalance-based cascade impactor found that highly charged particles can cause measurement biases.1 1 High voltage n Aerosol flow - Collected- particles / - - T \ Electrostatic and precipitation Piezoelectric crystal charging Fig. 3 Piezoelectric detector with electrostatic precipitator particle collection (Model 8510, TSI) for These instruments are available in both a single-stage, hand-portable instrument (Model 8510, TSI, St. Paul, MN, USA) and multiple-stage, cascade impactor instruments (Model C-lOOOA, QCM Research, Laguna Beach, CA, USA; PC-2, California Measurements, Sierra Madre, CA, USA). The hand-portable instrument can be used with reasonable accuracy for certain types of aerosols that are primarily respirable. This instrument uses an electrostatic precipitator and is not designed to be safe for use in explosive atmos- pheres.Condensation Nucleus Counters There is a commercially available portable condensation nucleus counter (Portacount, TSI) that has been used pri- marily for quantitative fit testing of respirators. 12 This device uses an ambient aerosol as a challenge aerosol. The condensa- tion nucleus counter (CNC) works by passing the aerosol through a supersaturated vapour (Fig. 4). The vapour condenses onto the particles so that they grow to a uniform size. The particle concentration is determined by counting with an OPC or measuring with a photometer. These instruments are in relatively common use and have been accepted by the Occupational Safety and Health Administra- tion as an alternative technique for quantitative fit testing.There are also miniature, fixed-location versions of the condensation nucleus counters that have been used for clean-room monitoring because of the CNC's ability to detect sub-micrometre particles. Oscillation Microbalance The tapered element oscillating microbalance (TEOM) (Rupprecht and Patashnick, Albany, NY , USA)lO currently belongs in a class by itself, as there are no other commercially available instruments that use a similar sensing element. It is not available as a portable instrument, but is included here as the general technique shows promise and is in an area of current development. The TEOM uses the resonant fre- quency of a tapered oscillating tube, on the end of which is a particle collection element, to determine the mass of the collected particles (Fig.5). The principle is the same as that of a pendulum, with the collected mass decreasing the resonant frequency of the sensor. The collection element is typically a Pump @ Filter Optical c.' detection Mw Condenser I I ' . I I Mask sampling Port Ambient sampling Port Switching valve Fig. 4 Condensation nucleus counter (PortaCount, TSI) sensor38 Analyst, January 1994, Vol. 11 9 small filter. At a sampling rate of 3 1 min-1, the manufacturer estimates the mass resolution to be +15 pg m-3 for a 2 min measurement. The coupling of the particles to the filter surface is usually much better than that for the piezoelectric crystal since the resonant frequency is much lower and the vibrational motion is parallel to the surface rather than perpendicular.Particles also adhere to the rough surface of a filter better than the smooth surface of a crystal. Hence these instruments are probably the most accurate direct-reading instruments for particulate mass. One version of this instru- ment has been certified for PM-10 ambient air monitoring by the Environmental Protection Agency. However, the instrument cannot be used as a portable monitor. Although the sensor is relatively compact, it is sensitive to temperature changes and vapour ( e . g . , water) condensation, so the air entering the sensor must be condi- tioned to a constant, higher than ambient temperature. The conditioning system makes the instrument large, expensive and relatively immobile. There was a development programme some years ago to build a device based on the TEOM sensor that could provide a respirable dust mass readout at the end of a work shift.13 This device worked successfully, but was not commercialized.With some additional research and development, a device based on the TEOM or similar oscillating sensor principles would be a very useful tool for compliance and research in the occupa- tional and indoor environment. Another instrument based on the oscillation of filter- collected aerosol was marketed for some time by Hund (Model MESA, Helmut Hund, Wetzlar, Germany). This device was based on a filter tape collection system that combined both mass measurement (from the resonant oscil- lation frequency of a clamped section of tape) and photometer measurement. The oscillating mass measurement was sub- sequently removed from the MESA instrument because of the cost and complexity of the mass detection mechanism.A device now under development by MIE (Bedford, MA, USA) is based on a circular filter clamped in a holder. The mass collected on the filter is sensed by the change in resonant frequency of the filter, which is made to vibrate like a drum. This effort is being supported by the US Bureau of Mines and is currently in its initial phase, so no further information is available. fiRadiation Attenuation Monitors Several devices have been developed that use the attenuation of @-radiation to indicate particle mass collected on a thin film or filter. The mass is approximately proportional to the difference in attenuation of @-radiation before and after the Temperature conditioned aerosol - i t - * Filter A.c.excitation Optical detection of resonant frequency - t - To pump Fig. 5 precht and Patashnick) sensor Tapered element oscillating microbalance (TEOM, Rup- particles are collected. The radiation counting process limits the precision with which mass measurements can be per- formed, thus limiting the sensitivity of the instrument. The radiation scattering that produces the observed attenuation is a function of electron density within the particles.10 For example, hydrogen-containing materials tend to have a lower attenuation than higher atomic mass elements. Several portable instruments of this type were marketed in the 1970s and early 1980s (GCA, now MIE), but are no longer available.These instruments required sampling periods from 1 min to hours, depending on concentration. There are several commercial fixed-location tape samplers that are used to monitor environmental concentrations of aerosol. In this application, the instrument response time is not as critical, so sampling times of 21 h are acceptable. Aerodynamic Particle Sizers There are several commercial instruments based on the detection of particles with scattered light combined with particle acceleration. These instruments attempt to measure a useful parameter of aerosol behaviour directly, namely the aerodynamic diameter. These are basically research instruments that can be used for size distribution measure- ment in the field. The most common instrument of this type is the aerodynamic particle sizer (APS3300, TSI) .I4 It uses the accleration of particles through a nozzle and measurement of particle velocity to estimate aerodynamic size (Fig.6). A computer provides a sophisticated display of size distribution (0.5-30 pm) and allows the calculation of a number of other parameters. The acceleration field of this instrument is high enough that true aerodynamic diameter is not measured directly and adjustments have to be made for particle density and shape. Liquid particles may also distort in the acceleration field and appear smaller. Because of the more complex detection system, coincidence artefacts can appear in the detected size distribution. Phantom particles are produced throughout the detected size range, mainly as a result of partially detected small particles.Another instrument that uses a similar detection system is the Aerosizer (Amherst Process Instruments, Amherst, MA, USA).14 This device uses a critical flow nozzle as the particle accelerating device, resulting in sonic flow. This higher velocity requires even larger corrections to be made for calculating aerodynamic diameter. The Aerosizer has a larger measurement size range (0.2-200 pm) than the APS and can be used at higher concentrations. Another instrument, developed in Russia, is marketed by GIV (Breuberg, Germany). There have been no published evaluations of this instrument, so it is difficult to assess its utility. The instrument is currently being improved by GIV in Total flow 5 I min-' Sensor flow Filter Sheath flow valve Focusing Acceleration Laser beams 0 nozzle Fig.6 Aerodynamic particle sizer (APS3300, TSI) sensorAnalyst, January 1994, Vol. 11 9 39 cooperation with the developers. This device uses an acceler- ating nozzle, but measures the particle acceleration in front of the nozzle. The acceleration is lower and an improved detection system reduces coincidence problems. The lower acceleration also has the advantage of reducing correction factors for particle density and shape. The low flow rate through the small sensing volume allows measurements of high aerosol concentrations, as in powder analysis, but may make it difficult to measure low concentrations. Another instrument, the electric single particle aerody- namic relaxation time analyser (ESPART, Hosakawa Micron International, Osaka, Japan) ,I4 accelerates particles by using either an acoustic or an electric field (for charged particles). The commercial version of this device is expensive and large and is primarily intended for measuring the size and charge of toner dust particles.However, there are several research versions in use that are more mobile. As the particle velocity relative to the surrounding air is relatively low, only small corrections are needed to estimate aerodynamic diameter. At a single operating frequency, the instrument has a sizing range of about 1.5 orders of magnitude. The frequency can be changed to extend the range, but this requires recalibration of the system. Fibrous Aerosol Monitors The fibrous aerosol monitor (Models FAM-1 and FM7400, MIE) was developed primarily to measure asbestos fibres.14JS The instrument operates by aligning fibres in a high-voltage oscillating electric field.The oscillation rotates the fibre in a plane perpendicular to the illumination from a laser beam. A detector senses the scattered light at right-angles to the laser beam (Fig. 7). The scattered light is sensed as a series of pulses for fibres and a relatively constant signal for compact particles. Hence fibres are preferentially detected and counted. The fibrous aerosol monitor has been widely used for monitoring asbestos removal operations. It provides a real- time indication of fibre concentration to evaluate the controls used to contain the asbestos aerosol. The instrument has not been demonstrated to be sufficiently accurate to replace the standard filter collection/phase contrast light microscope method for fibres.Another instrument operating on similar principles, but using a multidetector light-scattering system rather than fibre rotation, is under development by Hygenius (FACT-1000, Hygenius, Mississauga, Ontario, Canada). The instrument uses a high-speed data processing system to analyse scattering patterns in real time and classify particles according to length and diameter. The classified particle data are stored for readout and further analysis. Beam Mirror ai r Lase? beam mirror detector Fig. 7 Fibrous aerosol monitor (FAM-1, MIE) sensor Recommendations of ACGIH Workshop There is clearly room for improvement of direct-reading aerosol instruments for use in industrial hygiene.A recent workshop on direct-reading aerosol instruments, sponsored by the ACGIH,3 produced a series of recommendations addressing some areas of improvement. The recommenda- tions are being made to instrument manufacturers and to various national and international groups, including national industrial hygiene organizations, the American Society for Testing Materials (ASTM), American National Standards Institute (ANSI), the European Standards Organization (CEN) and the International Standards Organization (ISO). The first recommendation was to develop voluntary consen- sus standards on specifications, calibration and operation of direct-reading aerosol instruments. The standards should be developed for two specific types of instruments: those measuring number concentration and those measuring mass concentration.Part of this recommendation is to develop guidelines for manufacturers on how to present data on their instruments. This part could be implemented as a separate effort, as a full consensus standard usually takes many years. Such standards would reduce some of the confusion that results when comparing instrument manufacturers’ specifica- tions for their products. The second recommendation focused on the need for an accurate, portable, direct-reading aerosol mass monitor. A variety of instruments are commercially available, but they measure a surrogate parameter for mass, e.g., photometers measure light scattering. These instruments need calibration for the specific aerosol size and material being measured. Microbalances are available, some based on piezoelectric crystals and others based on the tapered element oscillator.The piezobalances have problems with non-uniform sensitiv- ity on their surface, frequent cleaning requirements and adequate coupling of collected particles to the crystal surface for various types and sizes of particles. The tapered element oscillating microbalance (TEOM) meets most of the require- ments, but is not available in a portable instrument. This recommendation has already been acted upon. As mentioned previously, the US Bureau of Mines, responding to a request by the US Mine Safety and Health Administration, has funded the development of a direct-reading mass monitor based on an oscillating filter membrane. Another recommendation was to provide additional educa- tion and promotion in the industrial hygiene community to utilize more fully the capabilities of direct-reading aerosol instrumentation. Some possible mechanisms for providing this education could be through development of video training tapes, short courses and improved instructional materials. Finally, it was recommended that manufacturers follow quality assurance guidelines for the manufacture of their instruments, e.g., Guides 9000-9004 produced by the Interna- tional Standards Organization.Such an approach might remove some of the problems that have been observed in the past when instruments were produced that were unreliable. Marketing of such instruments resulted in users being discour- aged from using similar instruments.ngle Sampling Issues Although sampling efficiency is a more general aerosol measurement issue, it also applies to direct-reading instrumentation. Because of the ease with which numbers can be obtained with direct-reading instruments, sampling issues are often overlooked. The sampling biases produced at the inlet of an aerosol measuring system can be as great as or greater than some of the biases noted in the discussion of various instrument sensors. The inlets of many instruments40 Analyst, January 1994, Vol. 11 9 consist of a tube protruding from the side of the box enclosing the sensor. Little guidance is given to the user with regard to sampling arrangements or an indication of potential losses under various wind conditions. Recent work on thin-walled inlets has resulted in empirical algorithms for calculating sampling efficiencies.16 The situation with the sampling inlet projecting slightly from the surface of the instrument is represented better as a blunt sampler.This is an area of active research, so there is not a great deal of guidance for instrument users. 17 Many of the instrument sensors require that aerosol entering the instrument be uniformly distributed in the flow stream. If there is a pre-classifier upstream of the sensor, this may not always be the case. For instance, a cyclone will create a vortex in the exit stream. The aerosol in this stream is likely to be non-uniformly distributed. Similarly, aerosol passing through an impactor is also non-uniformly distributed. For instruments that use impactors to deposit the detected aerosol on a surface, the deposit may not be uniform.Recent work indicates that larger particles sampled with a circular nozzle impactor will be deposited in a ring, while smaller particles will be deposited with something approaching a normal distribution.18 Such deposits may have important conse- quences for instruments that assume uniform sample deposi- tion. Further, aerosol losses may occur within the instrument by various mechanisms. If the instrument inlet and sample handling lines are not properly designed, particles smaller than about 0.1 pm may diffuse to the inlet and sample line walls; particles larger than about 3 ym in diameter may exhibit significant settling and impaction. In small-diameter sample handling lines, electrostatic losses may occur with charged particles, especially if the inlet and lines are non-conduc- tive.19.20 Particles larger than 15 pm typically exhibit order-of- magnitude or greater biases during aspiration into the inlet.In addition to losses, particle deposition on sensor surfaces may produce biases that increase with measurement time. For instance, some simple photometers expose the light source and detector windows to the aerosol stream, resulting in increased light scattering detected by the instrument. A detected increase in signal level occurs with aerosol exposure, biasing the measurement .21 Conclusions A variety of aerosol instrumentation for monitoring in the workplace is available and new instruments are being deve- loped. However, further work is needed, not only to improve the accuracy of these instruments but also to ensure that they are being used properly.This requires efforts by both the instrument manufacturers and the industrial hygiene com- munity to provide proper information and education in the use of these instruments. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 References Aerosol Measurement: Principles, Techniques, and Applica- tions, ed. Willeke, K., and Baron, P., Van Nostrand Reinhold, New York, 1993, p. 876. Air Sampling Instruments, ed. Hering, S . V., American Conference of Governmental Industrial Hygienists, Cincinnati, OH, 7th edn., 1989, p. 612. Baron, P., Appl. Occup. Environ. Hyg., 1991, 8,405. Soderholm, S. C., Ann. Occup. Hyg., 1989, 33, 301. Smith, W. J., Dekker, D. L., and Greenwood-Smith, R., Am. Ind. Hyg. Assoc. J . , 1986, 47, 779. Baron, P. A., in Symposium-Advances in Air Sampling, ACGIH, Asilomar, CA, 1988, p. 205. Gebhart, J., in Aerosol Measurement: Principles, Techniques, and Applications, ed. Willeke, K., and Baron, P., Van Nostrand Reinhold, New York, 1993, p. 313. Kerker, M., The Scattering of Light and Other Electromagnetic Radiation, Academic Press, New York, 1969, p. 666. American Conference of Governmental Industrial Hygienists, Ann. Am. Conf. Gov. Ind. Hyg., 1984, 11, 23. Williams, K., Fairchild, C., and Jaklevic, J., in Aerosol Measurement: Principles, Techniques, and Applications, ed. Willeke, K., and Baron, P., Van Nostrand Reinhold, New York, 1993, p. 296. Horton, K. D., Ball, M. H. E., and Mitchell, J. P., J. Aerosol Sci., 1992, 23, 505. Cheng, Y. S., in Aerosol Measurement: Principles, Techniques, and Applications, ed. Willeke, K., and Baron, P., Van Nostrand Reinhold, New York, 1993, p. 427. Patashnick, H., and Rupprecht, G., Personal Dust Exposure Monitor Based on the Tapered Element Oscillating Micro- balance, Rupprecht and Patashnick, Albany, NY, 1983. Baron, P. A., Mazumder, M. K., and Cheng, Y. S., in Aerosol Measurement: Principles, Techniques and Applications, ed. Willeke, K., and Baron, P. A., Van Nostrand Reinhold, New York, 1992, p. 381-409. Lilienfeld, P., Elterman, P., and Baron, P., Am. Ind. Hyg. Assoc. J . , 1979, 40, 270. Hangal, S., and Willeke, K., Environ. Sci. Technol., 1990, 24, 688. Vincent, J. H., J. Aerosol Sci., 1987, 18,487. Sethi, V., and John, W., Aerosol Sci., Technol., 1993, 18, 1. Liu, B. Y. H., Pui, D. Y. H., and Szymanski, W., Ann. Occup. Hyg., 1985,29, 251. Baron, P. A., and Deye, G. J., Am. Ind. Hyg., Assoc. J . , 1989, 51,51. Willeke, K., and DeGarmo, S. J., Appl. Ind. Hyg., 1988,3,263. Paper 310321 2 D Received June 4, 1993 Accepted September 3, 1993

ISSN:0003-2654    

DOI:10.1039/AN9941900035

出版商:RSC    

年代:1994

数据来源: RSC