October, 19501 CLARK 525 The Testing of Atmospheric Conditions in Theatres and Cinemas BY J. F. CLARK (Read at the meeting of the Society on Wednesday, May 3rd, 1950) SVNoPsIs-The terms on which theatre and cinema licences are granted usually include some requirements regarding the ventilation, and an investiga- tion has been carried out to test the adequacy of the conditions laid down in the licences. Temperatures, humidities and carbon dioxide concentration were determined at several points in each. It was found that temperature and humidity varied more with weather conditions than with the internal atmosphere, but the carbon dioxide content of the air was a reliable indication of the ventilation. In particular it was noticed that “stufiness” became apparent to the observer a t a carbon dioxide level of 15 to 20 parts per 10,000.A simple method of sampling and testing for carbon dioxide concentra- tion, accurate to 0.2 part per lu,uOO, was developed. Rapidity of sampling was essential because not infrequently adjustments of ventilation were made while sampling was in progress. With most systems of ventilation it was considered that the usual require- ments of a maximum of 10 parts per 10,000 was too stringent, since to maintain this level near draught screens and in high balconies an air supply that produced pronounced draughts in the more open parts of the auditorium was required. Ventilation giving a maximum of 15 parts of carbon dioxide in the least ventilated areas resulted in an average concentration of under 12 parts throughout the auditorium (corresponding to a rate of 700 to 800 cu.f t . of fresh air per head per hour) and this could be maintained by any efficient ventilating system without producing noticeable draughts. Theatres and cinemas were inspected at peak periods. CINEMAS and theatres are subject to licensing and control by local Justices of the Peace and in laying down the conditions under which a licence is granted an attempt is usually made to ensure that an adequate standard of ventilation is maintained. During a review of these conditions of licence it was decided to investigate the practicability of the Justices’ requirements. The standard of comfort and hygiene of an auditorium atmosphere depends on many factors, including temperature, humidity, outside weather conditions, arrangement of seating, supply of fresh air and its velocity, and suspended impurities; for control purposes it is desirable to have some index of an easily determinable nature to show the state of the air.It is not proposed to enter into a discussion of the whole question of ventilation here. That was very ably done some time ago by R. C. Frederick at an Institute of Chemistry lecture, and the monograph1 is available to anyone wishing to follow up the subject. We might briefly define an undesirable atmosphere in the circumstances we are now considering as one that has been too much used. It will be hot, humid, hazy (if smoking is permitted) and will contain too high a proportion of the products of respiration and, not infrequently, perspiration also.Such an atmospheric state is the result of an insufficient supply of fresh air, but an excessive supply, although more hygienic, may be almost as unpleasant if it results in a cold draughty hall. The object of adequate ventilation is to strike the mean between draughts and “ stuffiness.” The optimum temperature is a matter of personal preference and is relative to outside weather conditions and other factors. It is a matter of comfort more than health, and so may be regarded as something to be arranged by the manager to suit his patrons in com- petition with similar establishments. It should, however, be borne in mind that it is cheaper to use the bodily heat of an audience to warm the atmosphere than to supply warm air. This will be referred to later. Humidity is influenced both by the audience and by outside conditions, and also by526 CLARK: THE TESTING OF ATMOSPHERIC [Vol.75 the fact that in many modern buildings the air drawn in is washed by passing through a water spray. The katathermometer, by measuring rates of heat loss, gives a very useful indication of the combined effect of temperature, humidity and air flow, but unfortunately it is not a suitable instrument for operating in crowded cinemas in the dark, so that it was decided not to use it in the investigation. An interesting possibility in this direction would be the use of one of the “drinking birds” which appeared as toys a year or two ago. If such a device could be standardised or calibrated, it would provide a very simple wet kata, and it would only be necessary to take the rate of dipping.A large number of tests were made with a whirling hygrometer, from which it was found that the relative humidity was lower inside a building than outside, owing to the higher temperatures, but there was little consistency i,n the results. Calculated as the percentage of water vapour in the air, the humidity ran parallel with the atmospheric conditions on any particular occasion, but no correlation was found possible in the results from different theatres on different days. The method was discarded with regret, as it seemed a very suitable one by which managements could have checked the efficiency of ventilation for themselves. Respired air, of course, contains more carbon dioxide and water vapour than fresh air, and also contains in suspension moisture droplets which can carry infection.The hygienic reason for ventilation is the need for the removal of these droplets and the associated bacteria, and also the avoidance of the effect of high temperature and humidity on respiratory surfaces, which are rendered less resistant to infection. Since the attempt to assess ventilation conditions by humidity measurements proved unsuccessful, owing to the many contributory factors, the accepted method of using the carbon dioxide concentration as an index of the extent to which the air had been used was investigated. It cannot be regarded as more than an indicator, as in the worst ventilation conditions the amounts found are of no toxic significance. One of the first symptoms of an excessive carbon dioxide concentration is a diminution of the critical faculties and a tendency to hilarity, which might not be disadvantageous at times in theatres and cinemas, The normal carbon dioxide output of a man at complete rest is just over 0.5 cu.ft. per hour, which can increase to 2 or even 3 cu. ft. with heavy exertion. For women and children the amounts are less. The average output of an audience under normal conditions was taken as 0.6 cu. ft. per person per hour, and on this basis, knowing the carbon dioxide contents of the fresh air supply and the air in the auditorium, it is possible to calculate the rate of supply of fresh air in terms of cubic feet per hea.d per hour. Working on these lines, the testing of ventilation resolves itself into problems of sampling and estimation of carbon dioxide.A reasonable size of sample is desirable, to cover a small area rather than a single point, as the latter might consist of almost undiluted exhaled air. It should be taken at about the height of the faces of the audience, and with as little noise and fuss as possible, since the most useful time of sampling is when the house is full and settling down, and distracting circumstances are then unpopular. It must be taken fairly rapidly, in view of the fact that some economically-minded managers stop the fans for a while after the house has refilled, to allow the theatre to warm up from the body heat of the audience. In such instances, the immediate reaction to the knowledge that tests are being made is generally a speeding up of the ventilation fans.EXPERIMENTAL First tests were carried out with absorption trains using various absorbents, but the amount of air to be passed to give a weighable amount of carbon dioxide necessitated too rapid a flow for efficient absorption. A small calibrated electric pump was useless, in view of the varying resistance to gas flow in the tubes. More success followed the use of a standard hand pump drawing 125 ml. per stroke, but this, had to be used very slowly. The apparatus was cumbersome and attracted undue attention. With too slow a stroke, the full 125 ml. was not drawn, and too rapid a stroke meant incomplete absorption. In the latter event, with solid absorbents, a loss in weight was recorded in some instances, possibly because of the removal of fine particles of absorbent from the tubes by the pumping.In view of these difficulties, the attempt to combine sampling and estimation in one operation was discontinued, and sampling alone was done on the site. This was accomplished most successfully by blowing up football bladders, which, when fitted with well-greased glass stopcocks, proved most useful gas containers. They can be filled quickly and, if in good condition, will take 4 to 5 litres of air and hold it without determinable change for severalOctober, 19501 CONDITIONS I N THEATRES AND CINEMAS 527 days. Some apprehension was felt about the possible condensation of moisture inside the bladders and at first they were pumped up through a tube containing anhydrone, but this introduced complications, as allowances had to be made for loss in volume of the gas on drying. It was found that con- densation did not take place in the bladders if extreme changes in temperature were avoided.When exhausted they contain only 3 or 4ml. of residual air. -APPARATUS- A simple apparatus, shown in Fig. 1, was devised for the estimation of the carbon dioxide, and consisted of an aspirator and a bubbler. The aspirator was an ordinary 5-litre bottle with a pressure tube so that the internal gas pressure could be observed and adjusted to atmospheric. The bubbler consisted of a large test tube with a centre tube, blown into two bulbs, fitting fairly closely inside it. The absorbent was barium hydroxide, roughly 0.1 N , containing about 5 per cent. of barium chloride. The effect of this type of bubbler is that the gas is held below and between the bulbs in contact with the liquid and released in a stream of bubbles through two layers of absorbent.With the carbon dioxide concentrations experienced and rates of flow not exceeding 2 litres per hour, it was found that one bubbler was quite sufficient and no carbon dioxide was absorbed in a second tube connected in series. 5 LlTRE ASPlRATOR BUBBLER Fig. I FOOTBALL BLADDER METHOD- Ten millilitres of baryta were used in the tube and in a “blank” tube of the same type, kept closed during the passage of the air; the same pipette was used to measure into both tubes. After passing the air, the contents of the tube and the blank were washed into flasks with carbon dioxide-free water and titrated with oxalic acid adjusted to such a strength (approximately 0.084 N ) that 1 ml.was equivalent to 1 ml. of carbon dioxide gas under room conditions of temperature and pressure. Phenol thymol phthalein was found to be the most suitable indicator, with a good colour change and sensitive to 0-02ml. The titration gave a direct reading of the volume of carbon dioxide in the volume of air passed. The procedure was to connect the bubbler to the aspirator and the bladder to the bubbler. The bladder stopcock was partially and cautiously opened, and when the aspirator was in equilibrium with the bladder (at a pressure of about 30 cm. of water) the water was drawn from the aspirator into a measuring cylinder at a slow trickle. The control of pressure from the bladder enabled a very steady gas flow to be maintained.When about 2 litres had been drawn off (or less, if barium carbonate was seen to be forming quickly) the bladder stopcock was closed and the water st.ream continued until the pressure in the aspirator was atmospheric. The volume of water collected was taken as the volume of gas passed at atmospheric pressure.628 CLARK: THE TESTING OF ATMOSPHERIC p o l . 75 It was actually very slightly higher, owing to the amount of water vapour picked up by the gas on passing through the bubbler, but the difference is well within the experimental error. At all the theatres and cinemas, samples of street air were taken and, although on the outskirts of the town, or in the town itself on breezy days, the carbon dioxide concentration was steady at 3.2 to 3.6 parts per 10,000, on still days in the town it sometimes rose as high as 6 per 10,000.These figures were taken into’ account in assessing ventilation efficiency. RESULTS AND CONCLUSIONS- It was concluded from the investigation that the usual limit of 10 parts per 10,000 in any part of the auditorium (necessitating an air supply of 1000 cu. ft. per head per hour in the most sheltered areas) was too stringent to be effectively operated, as it involved violent draughts and an average carbon dioxide concentration of 7 to 8 parts per 10,000 throughout the theatre. With a concentration of 5 to 6 parts per 10,000 in the outside air, this level is impracticable. It was decided that a practical limit which could be reasonably enforced was 15 parts per 10,000 in any part of the auditorium.In a modern cinema, when this level is reached in the least ventilated areas, the average concentration is found to be below 12 parts per 10,000, corresponding with an air supply of 800 c x . ft. per head per hour. It was found that 15 parts per 10,000 was the approximate point where “stuffiness” became noticeable on entering from outside, although acclimatisation was very rapid. After a little experience it was quite possible to tell on going into a cinema whether the concentration was above or below this point. The main ventilation systems found in public halls are generally either “plenum” in the more modern buildings, or exhaust, in the older ones. They can be roughly distinguished as “push” and “pull” systems.In the plenum cinema arrangement, air is drawn through a fine wire mesh, washed by a water spray, and injected through grilles alongside the screen. It is exhausted through grilles situated under the balcony, in the roof at the back of the balcony and often high up on the back and side walls. The air distribution is good and few dead areas are found, these being generally in front of draught screens and at the back of the balcony. With such systems there is little difficulty in keeping the carbon dioxide content below the suggested limit, even with a packed house. Inefficient ventilation in such buildings means that the fans have been slowed down or stopped, which may have been done to allow the house to warm up. With the exhaust system, air is admitted or finds its way through doors, windows or grilles, and is withdrawn by exhaust fans from the walls or roof.Dead areas are plentiful, particularly in the centre of blocks of seats anti under balconies, and there is considerable difficulty in maintaining a good atmosphere with a full house. A cinema with an exhaust system was inspected at 9 p.m. one evening when the house was full, and concentrations of carbon dioxide ranging from 21 to 25 parts per 10,000 were found (outside air 3.5). Next morning, with a wind blowing and all the doors and windows open, the air on the ground floor was at the same concentration as the street air, but at the back of the balcony there was still 11 parts per 10,000. The same evening, again with a full house and the fans at full speed, the results ranged from 13 to 18 parts per 10,000-obviously an unsatisfactory system.A plenum system cinema, with a full house, gave figures from 12.1 to 17.6 (outside air 3.3). Next morning, the doors having been kept closed, the atmosphere was the same inside as outside the cinema. Re-inspected by arrangement with the management, the carbon dioxide ranged from 9.7 to 10-7, showing that the system was quite efficient. Samples taken from the inlet and exhaust ducts showed that the washing did not affect the carbon dioxide content of the incoming air, although it removed a surprising amount of dirt. In the main extraction duct the concentration was 11.3 parts per 10,000 and in one from under the balcony, 8-9. The hand pump and bladders proved very convenient for taking air samples from ducts and otherwise inaccessible places. A final point concerns a question which is often raised-the effect of smoking on the carbon dioxide content of the atmosphere.The amount of carbon dioxide produced from one cigarette is of the order of 0.02 cu. ft., and it is doubtful if the consumption of cigarettes exceeds on the average one per person per hour. Thus the additional carbon dioxide produced Some results from typical cinemas with these systems may be of interest.October, 19501 CONDITIONS I N THEATRES AND CINEMAS 529 by smoking is of the order of 3 per cent., which is far less than the individual variation in expired air. Much more significant than the increase in carbon dioxide is the haze produced, which is composed of minute droplets of tarry matter.In the darkness of a cinema this is kept down to a satisfactory level by the suggested ventilation rates, but it is worth remarking that countries which allow smoking in cinemas are, in my experience, in the minority. In well-lit theatres and concert halls where smoking is permitted, ventilation can almost be left to look after itself, since any system which will keep the atmosphere satisfactorily clear of tobacco smoke will ensure that the concentration of carbon dioxide is well below the suggested maximum limit. REFERENCE 1. Frederick, Robert C., ‘‘Ventilation Conditions-Xormal and Abnorimal, and Their Investigation, ” Royal Institute of Chemistry Monograph, 1929. CITY ANALYST’S DEPARTMENT, MOUNT PLEASANT, LIVERPOOL, 3. DISCUSSION MR. C.H. MANLEY said that, with regard to the question of smoking in cinemas, he understood (and he noted that Mr. Clark agreed) that in Australia smoking was forbidden in the auditorium, there being a half-time interval during which patrons could smoke and partake of refreshments. DR. H. E. Cox noticed that the author expressed the opinion that the proper limit for carbon dioxide was about 15 parts per 10,000, and he wondered whether i t could really be valid to arrive a t such a figure on a chemical basis alone. He thought the limits both of carbon dioxide and moisture needed to be related to their physiological effects. Much data on this had been accumulated in relation to submarines. The present problem should be studied in the light of experience in mines and submarines. MR.J. G. SHERRATT referred to the type of carbon dioxide absorption tube used by Mr. Clark and asked by what method the author had proved that it was fully effective. In the questioner’s experience there was risk of incomplete absorption because of the relatively large volume of air enclosed within each bubble, and he had discarded this type of tube in favour of one utilising glass beads moistened with barium hydroxide solution. MR. F. L. OKELL, in reply to Mr. Sherratt, said that the efficiency of a bubbler of the type used by Mr. Clark did not depend on the size of the gas bubbles, but on the narrow space, about half a millimetre, between the wet walls of the bulb and the outer vessel through which the gas had to pass in a thin layer. Between each “bubble,” the surfaces of the gas passage were re-moistened by the absorbent and the result was very efficient absorption.The original designer was G. Nevi11 Huntly, who was for many years a well- known member of the Society. MR. CLARK, in reply to Dr. Cox’s point, said that the carbon dioxide had no physiological significance in the concentrations ordinarily found in theatres and cinemas. It merely served as an indicator of the ventilation by showing the extent of dilution of exhaled air. The suggested limit of 15 parts per 10,000 had been decided on as a reasonable and attainable compromise between over-ventilation causing draughts and under-ventilation causing stuffiness. Mr. Frederick’s paper, to which he had referred, went much more thoroughly into the physiological effects of extremes of ventilation, and the data there had mostly been accumulated in connection with Admiralty work, with particular reference to atmospheres in confined spaces. If the bulbs of the bubbler fitted closely to the sides of the tube, a second bubbler in series did not absorb a determinable amount of carbon dioxide, and a known amount of carbon dioxide was completely recovered within the limitations of accuracy of the method. The bubbler had been successfully used for other carbon dioxide estimations such as the testing of self-raising flour and baking powder. It was, however, inadvisable to exceed about two-fifths of the absorptive power of the baryta. What would the physiologist say? His experience confirmed Mr. Okell’s statements regarding the efficiency of the bubbler.