March, 1977 CODE OF PRACTICE FOR USE OF GAS CYLINDERS 57 SAFETY IN ANALYTICAL LABORATORIES While safety in the chemical laboratory has been a matter of general concern for many years, interest in laboratory conditions and practices has been heightened by the recent introduction of the Health and Safety at Work Act. The laboratory concerned with analytical chemistry has, in addition to problems that occur in all laboratories, requirements that relate to its own particular work and the implications of these requirements have not been widely discussed in the literature.An occasional series of articles on aspects of safety of particular interest to analytical chemists is therefore to be published in Proceedings. It is hoped that these articles will provide a forum for further discussion, and correspondence on the individual articles and on all safety matters is invited.The first article, which takes the form of a code of practice for the use of gas cylinders in analytical laboratories, appears below. Code of Practice for the Use of Gas Cylinders in An a lyti ca I Laboratories About 2 years ago, the Analytical Chemist’s Committee (ACC) of Imperial Chemical Indus- tries Limited decided to set up a small team to study the use of gas cylinders in analytical laboratories and to recommend a code of practice.The team, comprising W. J. Cank (Mond Division), D. R. Deans (Petrochemicals Division), D. M. Peake (Imperial Metal Indus- tries) and L. F. C. Underwood (Petrochemicals Division), completed its task early in 1976 and, after taking account of comments from labora- tory managers and administration and safety officers in both the UK and Europe, the ACC approved the adoption of the code of practice for all of the Company’s analytical laboratories.The code evoked such widespread interest that it was decided to publish it in the belief that it would be of value to other analysts, and that it might stimulate constructive comment and discussion in what, for many laboratories, can be a difficult area.1. Scope The code covers the storage, transport, handling and use of gas cylinders in analytical laboratories only. Excluded from the code are the filling of cylinders, including the preparation of calibration mixtures, and pressure testing of cylinders and regulators. Also excluded is the transport of cylinders outside the laboratory.2. Gas Cylinder Hazards 2.1. Nature of the gas Gases should not be used without prior con- sideration being given to any hazards associated with them. If possible, use an alternative with a lower risk. The appropriate safety pre- cautions should be taken to safeguard personnel from any risk. Gases can be broadly classified as follows: 2.1.1.Inert asphyxiants (e.g., nitrogen, argon). This group of gases is non-toxic but can act as asphyxiants by displacing the air neces- sary to sustain life. 2.1.2. Toxic (e.g., sulpkur dioxide, Jzydrogen sulphide). Toxic gases in relatively low con- centrations may have adverse physiological effects. These effects will vary in form and degree depending on the gas.2.1.3. Flammable (e.g., butane, propane). The hazards associated with gases in this group are those of fire and explosion. Table I gives the flammability ranges (in air) of some of the more commonly used gases. There is a wide variation in flammability range for different gases. Ethylene oxide, for example, has explosive limits of 3-100% V/V in air, while butane has the relatively narrow range of Fire, possibly without explosion, will occur if a leak develops under conditions where the gas immediately comes into contact with a source of ignition (hydrogen escaping a t high pressure may ignite spontaneously).However, if igni- tion is delayed, an explosion (external to the 1.9-8.5% V/V.58 CODE OF PRACTICE FOR USE OF GAS CYLINDERS Proc. AnaZyt. Div. Chem.Soc. TABLE I FLAMMABILITY RANGES OF GASES IN AIR Gas Hydrogen . . Methane .. Acetylene . . Ethane . . Ethylene . . Cyclopropane . . Butane .. Butenes .. Carbon monoxide Ethylene oxide. . Methyl chloride Methylamine . . Ammonia . . Hydrogen sulphide Propane .. Explosive limits, yo V/V in air .. 4-75 .. 5-15 . . 3-52 . . 3-12.5 . . 3.1-32 . . 2.2-9.5 . . 2.4-10.4 . . 1.9-8.5 . .1.6-9.7 .. 12.5-74 , . 3-100 . . 10.7-17.4 . . 4.9-20.8 . . 16-25 . . 4.3-46 cylinder) will occur provided that the concen- tration of the gas in air, at the time of ignition, lies between the explosive limits of the particu- lar gas. Sources of ignition can include sparks from static discharges to or from cylinders. 2.1.4. Corrosive (e.g., chlorine, sulphur di- oxide). Gases in this category are usually toxic and corrosive.Most are lachrymatory and will irritate the skin, and some can be absorbed through the skin. 2.1.5. Decomposition. Some gases, particu- larly acetylene, can decompose spontaneously when stored under pressure. Above pressures of about 9 p.s.i.g., undissolved (free) acetylene will begin to dissociate (decompose) and revert to its basic elements, viz., carbon and hydrogen.Considerable amounts of heat are given off during dissociation and may result in explosions of great violence. For this reason, acetylene is dissolved in acetone contained in a porous material (massing) inside the cylinder. If a void should occur in the porous mass of a cylinder of dissolved acetylene, then the acetylene may decompose. This decomposition may be initiated by some mechanical shock, such as dropping the cylinder.The voids in the porous mass can occur through natural settling of the mass or through damage to the cylinder in the form of denting. 2.1.6. Others (e.g.. oxygen, compressed air). Small increases in oxygen concentration greatly increase the fire hazard. An oxygen-enriched atmosphere will permit the burning of sub- stances that are not readily combustible in ordinary air.Fluorine and chlorine trifluoride, both of which are toxic, are very reactive chemically; in contact with many substances these gases will cause spontaneous fires and very vigorous burning can occur. 2.2. Density of gases Gases heavier than air can travel considerable distances and accumulate at a lower level than the source of a leak, thus producing an explosive or toxic hazard at a remote point.Leaks of gases lighter than air tend to be self-venting but can be trapped at higher levels than the leak. Hydrogen in particular can present an explosive hazard in this way. 2,3. Liquefied gas Dangers can exist due to hydraulic pressure if cylinders are not filled to the correct ullage or if subjected to a temperature increase (above 45 “C is considered unsafe).Liquefied gas cylinders should not be placed close to the surface of radiators, steam pipes, ovens, etc. 2.4. Gas cylinder identification It is essential to know what gas is contained in a given cylinder. All cylinders must therefore be clearly labelled with regard to their contents. For normal industrial gases, labelling according to BS 349:1973 is recommended.Commercial industrial gas cylinders should normally be colour coded according to the above British Standard. Colour codes can be ambiguous ; “industrial” gas colour codes are different from those for “medical gases.” This ambiguity can present a considerable hazard when both types of cylinders may be in use. The colour coding of gas pipes and hoses, which may be supplied with gas from cylinders, is not standardised.Consequently, any colour- coded pipes that are to be connected through a suitable regulator to the cylinder are likely to be colour coded differently. The main hazard is that it is not necessarily correct to connect a cylinder of one colour code to a pipe of the same. colour code. As a further means of distinguishing between flammable and non-flammable gases, the cylin- der valve outlets are screwed left-hand and right-hand, respectively.The outlets of valves for oxygen cylinders are screwed right-hand, as oxygen itself is non-flammable. The valve outlets of American helium cylinders have left- hand threads, although the gas is non-flammable. Hazards can arise through the use of an incorrect regulator on a cylinder.For instance, acetylene regulators should not be used onMarch, 1977 CODE OF PRACTICE FOR USE OF GAS CYLINDERS 59 hydrogen cylinders, which are filled to a higher pressure. The gauge for hydrogen is up to 3 000 p.s.i. but for acetylene 600 p.s.i. 2.5. Accidental escapes of gas Accidental escapes of gas will give rise to the hazards outlined in Section 2.1.Hazardous conditions may also arise if the escaping gas comes into contact with a substance with which it is chemically reactive. Such escapes may be occasioned by, for example, a defective cylinder valve or failure to close the valve properly, non- tight gas connections and defective hoses, pipes or connected apparatus. - 2.6. Gas pressure Some hazards arise only because the gas in a cylinder is at a pressure greater than atmos- pheric.For example, there is the risk of bursting should a cylinder receive a severe mechanical blow, or as the result of a pressure rise following an increase in temperature, such as involvement in a fire. Should the cylinder valve be broken off, the contents of the cylinder will be discharged to the atmosphere in an un- controlled manner, creating the risk of fire, explosion, poisoning or asphyxiation (depending on the gas), and the cylinder could, in some circumstances, be propelled like a rocket, so causing considerable damage. A considerable amount of energy is stored in a gas cylinder.For example, a 5.7-m3 cylinder when charged to 172 bar (2 500 p.s.i.g.) con- tains the energy equivalent to the contents of a small high-explosive shell.It is important to ensure that fittings and apparatus (on the high-pressure side of an installation) will safely withstand the maximum pressure of the cylinders that are to be connected. 2.7. Cylinder masses Cylinders in common use weigh between 23 and 113 kg when fully charged but are also of considerable mass when empty. Personal injury could arise through mishandling or insecure positioning.The dropping of a cylinder could result in damage to the cylinder with the associated hazards (see Section 2.6). 3. Example of Instructions for the Use of Gas Cylinders in Analytical Laboratories These instructions are intended as a guide, and the actual instructions issued at any site should take into account any local conditions and in particular local emergency procedures, which may differ from those included.Specific start-up and shut-down instructions should be provided for each major analytical installation incorporating gas cylinders. 3.1 Storage No part of any working area should be used for the purpose of long-term storage of gas cylinders. The number of gas cylinders held in the laboratory should be kept to the minimum necessary to meet working requirements.If a cylinder of a little used gas, particularly if corrosive, is kept in a laboratory for a lengthy period, it should be inspected periodically by a “competent” person. 3.2. Movement Cylinders should always be handled carefully and should not be allowed to receive blows likely to damage them or their valves, e.g., by being dropped on to unyielding surfaces.The mass of large cylinders makes it essential that they should always be moved in a cylinder carrier or trolley, which are available com- mercially. Staff should have instruction in kinetic handling and lifting, to avoid the risk of personal injury through mishandling. A film3 is available on kinetic handling, which includes the lifting of cylinders. Cylinders should not be handled with greasy hands, gloves or rags.When provided, valve covers should be kept in position in order to protect the valve during handling operations. 3.3 Correct use of cylinders 3.3.1. Size of cylinders. Whenever possible the size of cylinder should be such that the contents are used up within a reasonable time.3.3.2. Siting. Cylinders may be located in shelters outside the facility where the gas is required and the supply piped in. Any pipework should be designed by or approved by an engineer and include an isolation valve which can be operated from inside the laboratory. Cylinders may also be located in the laboratory. In both instances care must be taken to protect the cylinder from any source of heat likely to increase its temperature much above ambient.Care must also be taken to avoid contact with corrosive materials or dirt. Cylinders used in the open for lengthy periods should be protected from rain, snow and ice and consideration must be given to the effect that a decrease of the temperature to below ambient will have on the contents of the cylinder.Entrances, exits and passages must not be blocked by gas cylinders. 3.3.3. Care ‘and use of cylinder valves and fittings. Cylinder valves should be kept clean.60 CODE OF PRACTICE FOR USE OF GAS CYLINDERS PYOC. AnaZyt. Div. Chem. SOC. Loose dirt lying within the valve socket must be removed either by “snifting,” i.e., momen- tarily opening the valve to allow a small volume of gas to blow through, or preferably by blowing the dirt out with a compressed air-line if available.“Snifting” must not be carried out in confined spaces when toxic and/or flammable gases are involved, and in the latter instance not where there is any possibility of ignition. The operator should stand clear of the outlet while performing this operation. The cylinder valve must be cleared of loose dirt before fitting the regulator in order to allow it to seat properly.Only the standard key should be used to operate the valve spindle. Leverage must not be increased by any means, nor must excessive force be used. Valves should always be opened slowly. Some valves are fitted with non-captive spindles and care must be taken not to unscrew them too far (normally a half turn is sufficient).Cylinder valves and fittings should not be lubricated, except under specific advice from the gas supplier. On no account should oil or grease be used on oxygen cylinders, because of the risk of fire or explosion. Gas cylinders, valves and safety valves must never be repaired or modified by unskilled people. Cylinders, their valves and fittings should not be handled with greasy hands, gloves or rags.3.3.4. Use of regulator. With permanent, i.e., non-liquid, gases, the cylinders must be fitted with a pressure-reducing valve and the gas distributed at a reduced pressure. A regulator of the correct type (with respect to the pressure and nature of the gas) must always be used when gas is required from a cylinder. The cylinder valve must not be used to regulate the flow of gas.With liquefied gases, control of the gas flow should be arranged in accordance with the supplier’s instructions, which may or may not advise the use of a regulator. When a cylinder is not in use the cylinder valve must be closed. 3.3.5. Stability of cylinders. Cylinders must be secured against unintended movement. Cylinder stands, clamps or cylinder trolleys can be used for this purpose.3.3.6. Special precautions f o r cylinders of acetylene, liquefied gas and ammonia. Acetylene cylinders and cylinders of liquefied gas must be used upright in order to avoid outflow of liquid (acetone in the case of acetylene) into the regulator. Joint fittings or piping made of copper or of an alloy that contains more than 70% of copper must not be used with acetylene cylinders.Acetylene in contact with copper can form copper acetylide, which will readily explode when subjected to friction, heat or impact. Fittings used to connect ammonia cylinders must not be made of copper or copper alloys because of their susceptibility to chemical attack. 3.3.7. Testing for leaks. Joints in fittings and piping can be tested for leak-tightness by applying a soap solution.With fluorine, use a filter-paper soaked in potassium iodide solution, when a brown stain will appear at the leak. There are commercially available leak detectors for specific gases and explosion meters to detect leaks of hydrogen, etc. Leaks can also be detected by closing all exits, pressurising the system and isolating the inlet, then observing any pressure drops in the system with time.When particularly hazardous gases are to be used, the advisability of installing continuous leak detectors should be considered. 3.3.8. Pressure gauges. Pressure gauges for use with oxygen should be permanently and plainly marked “Oxygen.” They should be used as supplied and not allowed to become contaminated with oil, as an explosion may result from contact between oil and oxygen under pressure.The maximum scale reading of any pressure gauge connected to a gas installation should be at least one third greater than the greatest pressure to be applied to that gauge. This includes gauges used to indicate cylinder pressure (unless the gauge is specifically marked for full-scale operation).3.3.9. Miscellaneous. Cylinders should not be allowed to come into contact with electrical apparatus. Cylinders, whether charged or empty, must not be used as rollers for moving equipment. Personnel responsible for the acceptance of gas cylinders should satisfy themselves that the cylinders supplied are undamaged and that the contents are readily identifiable. When in doubt the cylinder should not be used and the supplier should be notified. The valve on an empty gas cylinder must be closed, and any protecting valve cover replaced.Also, the cylinder must be marked “empty.’J Air and moisture should not be allowed to enter cylinders (air would present a decontamina- tion problem to the supplier, and moisture would present a corrosion risk). This could occur if a cylinder was emptied and the valve left open.For these reasons, cylinders should not be completely blown down, but a slight pressure should always remain in them.March, 1977 CODE OF PRACTICE FOR USE OF GAS CYLINDERS 61 3.4. Emergency firocedures 3.4.1. Fire. In all instances of fire, raise the fire alarm locally, which should immediately bring into operation local procedures; if neces- sary call the Fire Brigade; don breathing apparatus. When fire has originated in other material, try to extinguish the fire.If it is safe to do so, remove from the area cylinders not yet involved in the fire; ensure valves are properly closed. Cylinders that have become heated should be left where they are pending the arrival of the Fire Brigade. If safe to do so, they should be cooled by copious hosing.When flammable gas leaking from a cylinder is burning at or near the source of the leak, try, to close the valve. Try to remove any material being burned by the flame, using tongs for this purpose. If neither of these actions is possible apply a suitable extinguishing agent to any burning material, but never try to extinguish the gas flame itself other than by closing the valve.Do not spray water on to a cylinder of liquefied petroleum gas where the escape of gas is burning, as this could increase the output of gas where the cylinder has become cooler than ambient. When flammable gas is leaking from a cylinder but not burning, try to close the valve. Extinguish any means of ignition. Remove the cylinder into the open if possible. If not, evacuate the building and inform the site emer- gency service. When a cylinder of acetylene is thought to be “burning” internally (i.e ., the acetylene is undergoing decomposition), as evidenced by a hot spot on the cylinder wall, close the valve, .warn persons in the vicinity and tell them to leave the area.Call the Fire Brigade, then inform the suppliers as soon as possible-do not wait until the cylinder is thought to besafe.The Fire Brigade should deal with the cylinder until the supplier’s representative arrives. When any fire incident is over, never attempt to examine, use or tamper with a cylinder that has been involved; always inform the suppliers and allow them to take appropriate action. 3.4.2. Toxic gas leaks.If no respiratory protection is available, evacuate the area and inform the site emergency service. If canister-type gas respirators (“gas masks”) of a type specifically approved for the gas con- cerned are readily available, don a respirator and, if the leak is small, try to stop i t ; if not immediately successful, leave the area. If the leak is large, leave the area at once and inform the site emergency service.Warning. Canister-type gas respirators will not give protection against high concentra- tions of gas. Generally, 30-min protection will be available provided the gas concentration does not exceed 1 yo. The use of self-air sets is preferable provided that another person similarly equipped is standing by to effect rescue if necessary. NOTE: There may be a need to wear pro- tective clothing, e.g., against chlorine trifluoride. 3.4.3. Inert asphyxiant gas leak. If the leak is small, try to stop it, but if it is large leave the area and inform the site emergency services. 3.4.4, Shearing off of cylinder valve. If a gas cylinder valve is sheared off, there will be an uncontrolled outflow of gas, and there is a possibility of the cylinder becoming jet propelled. Evacuate the area and inform the site emergency service. 4. Statutory Requirements following Government Regulations : Cylinders of gases are covered by parts of the 1. Petroleum (Consolidation) Act 1928, CH 2. The Petroleum (Compressed Gases) Order 3. The Highly Flammable Liquids and Liquefied Petroleum Gases Regulations Explosives Act 1875, Order in Council No. 32. 1930. 1972. 30. 4. 5. Bibliography 1. UK Atomic Energy Authority, “Safety in the Use of Gas Cylinders,” A.H.S.B. Rep., A.H.S.B. ( S ) R-84, 1965. 2. ‘*Identification of Contents of Industrial Gas Containers,” BS 349 : 1973. 3. “Make Light of Lifting,’’ ICI Film Library, London. 4. “Matheson Gas Data Book,” Fourth Edition, Herst Litho Inc., New York, 1966.