Document reYx5k37e11YBJrpJJ46YnGvE

19 What Should We Expect of Respirators? By ALLEN D. BRANDT, Sc. D. Willson Products, Inc,, Hcudimj, Pa, The important features to look for are: comfort, no interfer ence with vision, large filtering area, high filtering efficiency, low resistance, and small dead air space A chemical filter respirator. the hazard in industry was extremely mild compared to that in war. Secondly, the resistance to breathing in gas masks HE need for, .-scientific control of Tatmospheric pollution has long been recognized but to a large extent was too great for the untrained work man. Consequently respirators, mostly of the mechanical Alter type were intro neglected. The recent economic disturbdu ced in industry rather generally. ance with its million dollar rackets has Practically all of the earlier respira forced the issue, and today industry is tors had small filter areas. .Many of fully cognizant of the value, both eco them were of the pig snout type which nomic and humane, of atmospheric pol had an effective filtering area of about lution control. five square inches. To keep down the Control of atmospheric pollution is breathing resistance it was necessary to largely an engineering problem. From have a rather porous filtering material the engineering point of view, there are which obviously was not very effective at present four important specific meth in dust retention. ods of decreasing the worker's exposure: As early as 1919 Fieldner of the I. Control of polluting materials at point ot generation. 2. Isolation of hazardous processes. J. Substitution of non-hazardous processes. 4. Reduction of amount of polluting ma terial in inspired air by means of respiratory protective devices. Bureau of Mines indicated very defi nitely the need for a respirator of large filtering area for industry, and in 1926 Katz. Smith and Meiter further empha sized the advantages of large filtering area.1,3 They went so far as to construct a respirator in the form of a hat which While the use of respirators is listed as one of the methods of controlling the hazard, respirators do not control dust or other polluting material: they merely decrease the wearer's exposure. Hence the wearing of respirators is a method of industrial disease prevention, but not a method of atmospheric pollution con trol. The use of respiratory devices is not of recent origin. Various types of res pirators have been in use since the days of Agricola, but they were not widely had a large effective filtering area. 'T'o my knowledge, however, this device has never been used in industry. The Burrell and Fogler masks3 have large filtering areas in the form of a knapsack which is worn at the waist. They never became popular in industry because the knapsack type filters were burdensome and the face masks used with them covered the entire face. It was not until about 1930 that a large filter area (about 60 square inches) was introduced. used in industry till after the war. Un doubtedly the widespread use of gas Modem Respirators masks in the war had a direct influence upon the more general introduction of masks of different types in industry. Army gas masks were unsatisfactory in industry, even though they afforded effective protection. In the first place. The respirators found in industry to day may be divided into three general classes: l. Mechanical niter respirators which pro tect the wearer by littering out atmospheric particulate matter from the inspired air. JUNE. 1936 2. Chemical filter respirators which neutral ize or absorb harmful gases or vapors. 3. Supplied air respirators in which air from an uncontaminated source is forced througu tubing to the wearer. The mechanical filter respirator filters out a certain percentage of the dusts, fumes or mists from the inspired air. Obviously a filter respirator should ful fill the following requirements; 1. Should be comfortable and fit the face well, affording an air-tight contact between the face and the mask. 2. Should have no interference with vision and permit the use of glasses or goggles. 3. Should have a highly effective filter which is not bulky. 4. Should have low resistance to breathing over a period of use. 3. Should have small dead air space. 6. Should have both inhalation and exhala tion valves. Filter respirators are usually con structed of a rubber or part rubber face piece and a filtering medium of felted A mechanical filter respirator .i familiar pig-snout t\p* :o A -upplied air respirator of the air line type. material or paper-like material. Exhala tion valves are now almost universal. The more common type is the flutter or Saad valve which usually serves also as a drain for the perspiration and con densed moisture. Inhalation valves are supplied in many of the respirators at present in use in industry. The value of inhalation valves is not generally recognized. They serve two useful purposes. First, they prevent the very humid exhaled air from getting into and fouling the filter, and. second, they prevent rebreathing exhaled air in res pirators which have a dead space in the niter unit or in the filter chamber. Many people think that because a respirator is supplied with a good ex halation valve the exhaled air all passes nut through it, but such is not the case. In any system of air flow where there are two or more pa 'is which the air may take, the volume ,,uich will go through each path is inversely proportional to the resistance through each respective path. In other words, if the resistance through the exhalation valve of a res pirator is the same as the resistance through the filter, one half of the ex haled air will go out through the filter if there is no inhalation valve to prevent it. Rebreathing exhaled air. which has a high carbon dioxide content, induces panting and causes the wearer to think there is a lack of air and the resistance is very high. To eliminate these diffi culties. he will figure out several solu tions. all of which will seriously impair The performance of the respirator. The efficiency of dust retention by a filtering medium of felted or paper-like material of unit thickness is influenced directly by the density of. or resistance tn the air flow through the niter. With the same filter material, the resistance is influenced inversely by the area of the filter surface, hence keeping the re sistance to air flow constant the effi ciency of dust retention is influenced di rectly by the area of the filter surface. Furthermore, with other conditions constant, the increase in resistance over a period of use is inversely influenced by the area of filtering surface. This demonstrates dearly what Fieidner and Katz showed over a decade ago; namely, the area of the filtering surface is very important in the selection of a respira tor. The hazards, as well as conditions of use of respirators in industry, are many and varied. It is as illogical to recom mend the same respirator for all pur poses as it is to expect to find a respira tor specifically designed for each differ ent operation. Xo one would use the same respirator for hay fever preven tion that he would wear if he were ex posed to a dangerous concentration of quartz. In the selection of the proper respirator for any particular operation, it is important that the buyer specify the conditions as fully as possible when asking for recommendations from res pirator manufacturers or preferably from impartial consultants, such as the Bu reau of Mines. Care and Inspection Where respirators are being used, as with any system of dust control, routine inspection is essential. If a large number of respirators is employed in any one A mechanical filter respirator with increased filtering area. Approved by the t". Bureau of Mines. industry-, it is advisable to designate one man. part or all of whose work is, to inspect respirators both while being worn and when not in use. The damaged or unsatisfactory' parts should be re placed by new parts: the respirators should be cleaned and sterilized regu larly. ' When the respirators are in actual service, this routine inspector should see A supplied air respirator of the abra sive blasting type. that they are worn properly and that all parts are functioning as intended. This inspection is very important because it is not long until the wearer will have learned a thousand and one ways to de crease the breathing resistance f such as placing a chip of wood or punching a hole in the exhaust valve, leaving out the filter, or one of them if two are recommended, wearing the headbands loose so that the air enters between the mask edge and the face, pushing several holes through the filter with a pointed stick, screwing on loosely the connection which holds the filter, and others) which invariably affect its performance seri ously. With those thoughts in mind it is veryapparent that a respirator should have its parts easily replaceable and the func tioning parts, such as the exhaust valve and filter element, should be readily visible so that no time is lost in remov ing the respirator from the wearer for inspection. Efficiency Tests While nothing has been published, it has long been known by Drinker and others that the efficiency of dust reten- (Please turn to page 64) NATIONAL SAFETY NEWS