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REVENTION of dust inhalation by the wear P ing of cloths, handkerchiefs, and the like over the nose and (mouth was practiced in Agri Uses cola's time. Such devices, crude as they were, and Limitations reduced the discomforts of breathing smoky or dusty air. Although the medieval metallurgists lacked our chemical and medical names for their of RESPIRATORY respiratory hazards, they understood the physio logic effects of carbon monoxide, and Agricola's Protective EQUIPMENTremarks about silicosis among the Carpathian miners showed chat this disease was well known. The invention of che diving suit by Siebe early in the nineteenth century demonstrated that it was perfectly practicable for a man to breathe air By PHILIP DRINKER blown to him through a hose connected to a SCHOOL OF PUBLIC HEALTH. HARVARD UNIVERSITY, BOSTON, MASS. blower some distance away. The modem hose mask and the simpler air-line respirators remind one of Siebe's original equipment. It was not until the close of the World War, however, that industry in general began to appreciate the industrial possibili ties of gas masks, dust respirators, and other respiratory protec must not be too heavy--all of these items being subject to cer tain latitude. The amount of air breathed and the oxygen consumed by the average healthy 150-lb man is given in Table 1. tive equipment. In 1911 the U. S. Bureau of Mines began issu TABLE 1 AIR BREATHED AND OXYGEN CONSUMED ing literature on oxygen-breathing apparatus, but it was not until 1919 that the systematic development of modem respira tory protective equipment began. A respirator is a device for rendering inhaled air respirable. In recent years the word has been applied especially to devices for protection against dust inhalation, but the broader use of the term is preferable. Brown (l)1 has suggested the following classification of respirators: I Supplied-air respirators (After Henderson and Haggard) Oxygen consumption, liters per min Rest in bed, fasting........... .... Sitting................................. ... Standing.............................. ... Walking, 2 mph................. ... Walking, 4 mph.................. ... Slow run.............................. ... Maximum exertion............-- 0.240 0.300 0.360 0.650 1.200 2.000 3 to 4 . Air breathed, liters per min 6 7 6 14 26 43 65-100 A Self-contained type 1 Oxygen breathing apparatus B Hose type 1 Hose mask 2 Air-line respirator 3 Abrasive-blasting respirator II Air-purifying respirators It was decided in the gas-mask studies carried out during the War that 85 liters per minute represented the maximum amount of air likely to pass through a mask at either inspiration or expiration. Of course no one but the exceptional person, such as a long-distance runner, breathes at 85 1pm for more than a few moments, but half that rate, or 42.5 1pm, is not unusual. Since one inspires approximately one-half the time and expires A Chemical-filter respirator the other half, the actual minute volume breathed should be 1 Acid-gas, or type A doubled,1 hence the figure of 85 1pm; and it is this figure 2 Organic-vapor, or type B which is commonly used in measuring resistance. Measure 3 Ammonia, or type C ment is made with the 4 Carbon monoxide, or type D aid of simple set-up illus 3 Combinations of 1, 2, 3, and 4 trated in Fig. 1 precisely B Mechanical-filter respirator as one measures pressure 1 Dust, or type A differences in air ducts 2 Fume, or type B or in chimneys. The 3 Mist, or type C muscles which raise and 4 Combinations of 1, 2, and 3 lower the chest in res C Chemical- and mechanical-filter respirator piration are not strong 1 All combinations of A and B above (Group II) and easily become tired if GENERAL REQUIREMENTS overworked. Any seri ous impediment to inspi There are several important considerations applicable to ration. is fatiguing and all respiratory protective equipment: First, the device must causes a building up of not offer an annoying resistance either to inspiration or expira tion; secondly, it must afford a definite degree of protection under well-defined conditions; thirdly, it must be reasonably comfortable, it must not interfere unduly with vision, and it 1 Numbers in parentheses refer to similarly numbered items in the bibliography at the end of this papa. . Contributed by the Safety Committee and presented at a session on Occupational Diseases at the Annual Meeting, New York, N. Y., Dec. 2-6, 1933, of Tbs American Socistt or Mxchanical Enoinbeu. excessive carbon dioxide in the blood, a desire to breathe rapidly, and a degree of discomfort which quickly may be come so distressing as to no. 1 ARRANGEMENT FOR TESTING THE RESISTANCE TO AIR FLOW OF VARIOUS FORMS OF RESPIRATORS (R respirator, M -- water manome ter, F " flow meter with capacity of 85 liters per minute.) 1 Actually the respiratory cycle is usually irregular, but for mask testing it is permissible to consider it symmetrical and to ignore the pause at full inspiration or expiration. ---------------------- 171 PLAINTIFF'S ii; 172 Mechanical Engineer! cause che inexperi enced wearer of a mask to take ic off. Ic is nor difficulc to train oneself, to breathe against rather high resistances but this training requires che incentive of extreme hazards or the disci pline possible in war. It is not a practical peace-time expedient and should not be necessary. For gas masks the Bureau of Mines now allows an inspiratory resistance i of 3.5 in. and 1.5 in. to k expiration at 85 1pm. I In dust respirators the Bureau's sched ule permits maximum resistance of 2 in. to inspiration and 1 in. to expiration, all tests being made at the completion of filter ing-efficiency tests and no. 2 half-hour oxtgbn-bxbathinq noc simply when the APPARATUS---- APPROVES ST THB BUREAU device i*neW- TheSC op mznbs (2) resistances should be (Courtesy Mine Safety Appliances, Pittsburgh, Pa.) lowered from time to cime as general im provements in indus trial, respirators warrant more severe specifications, for it will be found chat even 2-in. resistance at 85 1pm is unpleasant for long periods. Oxygen-Breathing Apparatus. After a fire or explosion such as occurs in mines, rescue work must be quick, and the rescuers , must enter at mospheres of unknown composition. Often an. added difficulty .is dense smoke through which the visibility is poor. Rarely is there any chance for che use of hose-type equipment. In spite of such obstacles there are numerous records of rescues made by men wearing self- contained apparatus for which the wearer car ried his own oxygen supply. A modern oxygen-breathing outfit is shown in Fig. 2. Oxygen is carried in a small steel bottle which leads through a special reducing valve to che breathing bag and then to the face piece. Since an average man engaged in fairly heavy exercise needs 2 to 3 liters of oxygen per minute, the exhaled air of the wearer of oxygen-breathing apparatus must be purified and re-used. Otherwise the man would be able to carry only a few minutes' oxygen supply. The regenerating and purifying device con sists essentially of a container or cartridge of a suitable carbon-dioxide absorber such as soda lime (NaiOCaO). The oxygen consumed is then made up by che addition of oxygen from che breathing tank. At altitudes in excess of about 15,000 ft ex perienced airplane pilots use oxygen-breathing equipment v: ing from a simple arrangement for giving che piloc an occasic breach of oxygen to complete equipment which must be w continually. At sea-level pressures, chere is no limit to gas concencracion against which an oxygen-breaching eqt ment protects, although it obviously cannot protect the we; against gases, like hydrocyanic acid, which are absor: through che skin. Host Mask. In Fig. 3 is shown a hose mask with the wca carrying out a task for which che device is particularly suit. Here the air hose must be strong enough to be used as a i line in emergencies, must be impermeable to oils, gasoline, a water, and must not collapse under heavy weight. Air is si plied by a hand-operated blower. As in the case of oxygen-breathing apparatus, there is limic co che atmospheres in which hose masks give safe proti cion, saving possible harm through skin absorption. T hose must be of sufficient diameter to let che wearer breathe case the operator of the pump should have to stop for a she interval. Ic is found chat a safe minimum hose diameter V* it>- It is impracticable co pump air by hand through lot lengths of hose and difficulc co breathe through more chan 1: ft should the air supply be cut off. Therefore, the device definitely limited to use in places where che blower can I placed within 150 ft of the wearer. The Bureau of Mines requires that the exhalation valve c che face piece shall noc have a resistance at 85 1pm of moi chan 1.3 in. Because of the danger of che hand-driven blower stopping occasionally, the inspiratory resistance through cl blower, che hose, and face piece should not exceed 2.3 in. Ic has been found safe for men to enter empty tank car shallow manholes, and the like with hose masks withouc blow ers. The wearer then breaches through a gas-proof hose an is safe as long as the inspiratory resistance of the hose is lot and che inlet of the hose remains in clean air. Such an arrange ment does not dispense with the need of a strong hose whic can serve as a life line in che event of some mishap co the weare March, 1936 173 of che mask, nor should it dispense wich an observer outside the zone of danger. - Air-Lint Respirators. The positive-pressure respirator, Fig. 4, worn in such jobs as paint spraying, is an outgrowth or simpli fication of the hose mask. It is adapted to all work in which there is no severe hazard to the wearer should he remove the device momentarily. That is, it should not be used in danger ous atmospheres to which the hose mask or the oxygen-breath ing apparatus is especially suited. Air-line respirators are much less expensive than hose masks, the air line may be of small bore compressed-air hose, and no life line is needed. If the air supply is cut off, the wearer simply removes his mask and moves out of the polluted air. In general, air-line respirators can be worn for long periods, as they are light and there is little discomfort to the wearer. As yet there are no specifications for these respirators, but their effectiveness can be judged satisfactorily by requiring the wearer co spray an emulsion of black pigment in water, and after some 15 or 20 minutes' typical spraying work, comparing his nasal discharge and sputum with specimens caken before spraying. Abrasive-Blasting Respirators. One of the severest dust haz ards is abrasive blasting of sandy castings with sand as the abrasive cleaner. Of less danger is blasting with scecl shot, but neither process should be permitted unless the blaster wears a respirator of the general type shown in Fig. 5- The device must protect the workman against flying particles and should be supplied with air at sufficient pressure and volume to insure a siighc but constanc positive pressure at the nose and mouth. Unfortunately, abra sive blasters are of ten the least intelli gent workmen in che plant. It is not at all uncommon to see the blaster finish a job, open the doors of che blasting chamber, cake off his helmet and then blow the loose material off the cast ings, thus making it certain that he will breathe dust he should avoid and that his helmet and his own head are well bathed in dust. Obviously, he will breath this dust when he puts on his helmet again. Respirators suitable for this work can be made in various forms. The essential specifi cation is that the wearer receives air substantially as clean as that from che com pressed-air line. Tests demonstrating this ( ^ fio. 5 abxasivb-blasiino respirator fact should be made (Courtesy W. W. Sly Manufacturing Com- under practical blast- pany, Cleveland, Ohio.) ing conditions--cests such as that suggested for air-line respirators are quick and will eliminate many poor abrasive-blasting respiracors, but final acceptance of a blasting respirator should rest upon a practical demonstration in which che air within the device is sampled and compared with that from the air line. It was suggested by Bloomfield and Greenburg (4) that air flows of at least 6 cfm per helmet were required but it is now recognized generally that less than 6 cfm often suffices. How ever, inestimating air flows co be supplied co blasting respirators at least 6 cfm per man should be allowed. Mo harm results from using too much air within the helmet while too little may result in negative pressures during inspiration. One can notice momentary pressure drops by the sensation on the ear drums, and che wearer should be taught to turn on enough air so chat he can not notice this change even on taking a deep breath. Air Purifiers. In most mines and in most dusty plants com pressed air is available, but is apt to be wet and smell objection ably of oil. Also it may be unpleasantly cold when expanded directly into a respirator. It is not difficult to clean, dry, and warm compressed air so that it is suitable for breathing. Various expedients can be adopted, one of which is shown in Fig. 6. Plants having no compressed air would do well either to in stall compressors in which the intake air has no concact with oil or else to use a rotary compressor capable of delivering air at a pressure of 10 to 20 lb per sq in. Obviously, the air sup plied should be free from harmful dusts. Accidents in which che intake of oil-lubricated compressors has been contaminated with che exhaust gas from gasoline-driven motors or in which some of che lubricating oil has been converted into carbon 174 Mechanical Engineering monoxide are much more common chan is generally supposed. Qumical-FiUtt Rtspiiators or Gas Masks. The Bureau of Mines has detailed specifications for the construction and per formance of gas masks which protect against any gas or against any combination of gases. In Fig. 7 is shown a so-called "all service mask" which protects against any combination of gases as well as against smokes and dusts. In general the most important ingredient in gas-mask can isters is activated carbon, about 8-14 mesh in size. Carbon of high adsorptive capacity is now obtainable and is controlled by exacting specifications. It is effective against dilute con centrations of such organic gases and vapors as gasoline, and has an appreciable effect against organic acids such as formic or acetic. Furthermore, a mask approved against mercury vapor contains charcoal as the essential air purifier. Of next importance is an alkaline absorbent such as soda lime, which reacts with acid gases such as carbon dioxide, sulphur dioxide, and hydrogen sulphide. Ammonia can be caught by silica gel (6) and by the special reagent, cupramite, which is activated carbon or pumice impregnated with copper sulphate (7). Carbon monoxide is not directly absorbed by any reagent but is converted by a special catalyst, hopcalite (8), into carbon dioxide and chat in turn is caught in soda lime. One of the important difficulties in carbon-monoxide adsorption is dissipation of the heat generated when the carbon monoxide is oxidized to the dioxide. This heat loss is realized by passing the oxidized gas through a special radiator on cop of the can ister. In general, gas masks will not procect against concentrations exceeding 2 to 3 per cent of the inspired air and of course they will not make up for oxygen deficiency. Their life lasts only as long as the ingredients of the canister retain their required efficiency. Some masks, such as that shown in Fig. 7, are ob tainable with timing devices which are actuated by the wear er's respiration and thus show when the canister should be re newed. no. 6 aix-purifiex (Courtesy E. D. Bullard Co., San Francisco, Calif.) I I \ )- O no. 7 AIX-SBRVICB MASK--APFBOVBD BY BUREAU OF MUTES (5) (Courtesy Mine Safety Appliances Company, Pittsburgh, Pa.) Chtmical-Carttidft Respirators. There are many jobs in which some protection against gases is welcome but the lack of such protection does not involve a serious risk. In Fig. 8 is shown a cartridge-type respirator which is used for protection against low concentrations of such gases as gasoline and sulphur dioxide, and in certain paint-spray jobs. Obviously, such a device is cheaper than an air-line respirator or gas mask and attracts purchasers accordingly. It is not a substitute for either of these devices and should never be used for protection against severe hazards. In its favor are its extreme simplicity and the readiness with which expended cartridges can be renewed. Mechanical-Filter orDuss Respirators. These devices are intended to protect only against particulate matter and are not to be used against gases. As the result of the formulation by the Bureau of Mines of an approval schedule (9), dust respirators have been improved greatly and now are available in efficient forms with low resistance co breathing, Fig. 9. Dust respirators, unlike the filters of commercial dust col lectors, must be highly efficient at the outset--they cannot rely upon usage or dusting to plug the pores of the filter substance and thus improve the dust catching. It is not an easy matter to catch such substances as finely divided lead fume or fine quartz dust and still have a device through which the untrained wearer can breathe with reasonable comfort. In general the filter materials now in use in the approved res pirators are of wool felt or of specially impregnated paper (10) or various combinations of the two. Air -velocities through the fresh filters are about 20 fpm compared to 2 co 6 fpm used in commercial filter cloths for dust collection. It is generally recognized in practical respirator manufacture chat chin filcer March, 1936 175 than to supply approved devices which remain in the stock room or are worn only in the presence of superiors. DISCUSSION It can be said of all the mechanical-filter-type or dust respira tors that they are a poor substitute for dust control. Ulti mately it is not an economy to supply workmen with air-line respirators or with dust respirators instead of installing the proper dust-control equipment. Further, the time is not far off when the courts and compensation boards will make short shrift of the employer who lets his men work in dense clouds of dust, regardless of what the dust is. In general the employer would do well to try some of the dusty jobs himself, wear the men's respirators, and thus decide whether or not it would be better to install dust control in stead of respirators. However, dust respirators are centuries old; they have a legitimate place in industry, and are an im portant aid in the prevention of dust inhalation, but they ate not a substitute for dust prevention and never should be used as such. This sort of criticism does not apply with the same force to the other types of respirators. Oxygen-breathing apparatus, gas masks, and hose masks are all used in emergencies, usually resulting from accidents. Hose masks may be used routinely, but they are sold in single units while dust respirators are apt to be sold and used by the gross. Also, air-line respirators and abrasive-blasting respirators are often applicable to situations HO. 8 CHEMICAL-CARTRIDGE RESPIRATOR (Courtesy Willson Products, Inc., Reading, Pa.) substances plug rapidly. If they are used in respirators, pro vision for frequent changes of filters is necessary. Thick filters of wool felt; on the other hand, plug slowly but are too ex pensive to discard and are cleaned by compressed air or by shaking. There is every reason to believe that better filtering materials will be made, and it is important to noce that the Bureau of Mines' requirements permit the greatest latitude in the selec tion and manufacture of the filters. It is probable that the Bureau's resistance requirements, which are now more severe than those for gas masks, will be made still more severe in the future. Nonapprovtd Dust Respirators. There are many dusty jobs for which less effective dust respirators are suited. The Bureau's stamp of approval has in the eyes of many an unwarranted legal significance which has yet to be upheld in court. Some firms, driven panicky by the present silicosis-dust racket, have even gone so far as to stock up with ''approved" respirators so that they might be able to show they have on hand the best respira tors made in case they find themselves defending a dust-com pensation lawsuit. There is not the slightest reason to use the best respirators against flour, cocoa, limestone, cement, and many other dusts. It is more to the workman's interest to give him a less elaborate device which may be less effective but which is also more com fortable, Fig. 10. Indeed, there are jobs with high quartzdust exposure in which it would be much better to provide the men with nonapproved respirators which the men would wear FIG. 9 DUST RESPIRATOR FOR USB AGAINST LBAD AND SILICA DUST (8)--APPROVED BT THE BUREAU OF MINES (Courtesy Willson Products, Inc, Reading, Pa.) 176 Mechanical Engineerin in which the employer conscientiously has taken all reasonable precautions to prevent dustiness. At the present writing there are United States Bureau of Mines' specifications for approval of all of these devices ex cept the air-line and abrasive-blasting respirators. The American Standards Association and the Bureau of Mines are now preparing specifications for this complete list. The United States Navy and Army have further specifications for various types of equipment. The purpose of all such specifications-- certainly those of the Bureau of Mines--is to insure a product adequate for the protection needed, without putting undue re straint upon the respirator manufacturer's ingenuity. Care of Respirators. Because of their special construction and the composition of the chemical ingredients of various of these devices, their deterioration is fairly rapid. Companies like the utilities using them in considerable quantity maintain a regular repair service which sees that all equipment is inspected regularly and all is in first-class condition before being reissued. Generally, the firms which sell respirators furnish reliable direc tions for storing, cleaning, sterilizing, and repairing all equip ment. In conclusion the author wishes to make clear thac equipment of the type described in this paper ages rapidly--today's new models will appear on tomorrow's museum shelves. The Bu reau of Mines' approval, desirable as it is, does not tell the pur chaser which is the best equipment but merely insures him rh the approved article is what might be called "first-grade Testing these devices is a service offered by the Bureau for ci help of industry and it is to industry's advantage to patroni this service. REFERENCES 1 "Respiratory Protective Devices," by C. E. Brown and W. ; Yant, Trans. National Safety Council, 1935, p. 135. 2 "Procedure for Establishing a List of Permissible Self-Containt Oxygen-Breathing Apparatus," U. S. Bureau of Mines, Schedule 13/ Jan. 21, 1930. 3 "Procedure for Testing Hose Masks for Permissibility," U. ! Bureau of Mines, Schedule of April 28, 1927, and supplement of Augtr 20, 1934. 4 "Sand and Metallic Abrasive Blasting as an Industrial Hcalt Hazard," by J. J. Bloomfield and L. Greenburg, Journal Industrial H liens, vol. 15, 1933, p. 184. ' 5 "Procedure for Testing Gas Masks for Permissibility," U. S. Be reau of Mines, Schedule 14D of May 9, 1935. 6 U. S. Patent 1,586,327. 7 U. S. Patent 1,559,980. 8 "The Removal of Carbon Monoxide From Air," by A. B. Lamfc W. C. Bray, and J. C. W. Frazes, Journal, Industrial and Enghuerini Chen istry, vol. 12, 1920, p. 213. See also U. S. Pat. 1,345,323. 9 "Procedure for Testing Filter-Type Dust, Fume, and Mist Respin tors for Permissibility," U. S. Bureau of Mines, Schedule 21 of Augus 20, 1934. 10 (J. S. Patents 1,798,164; 1,814,190; 1,818,155. 1': tr no. 10 OUST ZBSratATOa. rox USB against dusts such as zinc oxide, cocoa, roue, and soda ash (Courtesy Willson Products, Inc., Reading, Pa.)