Document pBy38DDqDEb4LxNYXoGYwzZRD

76- B. A responsible person should he assigned the task of supervis ing maintenance and housekeeping activities. Among other things he should cake tests from time to tine to cake sure than the dust control program is achieving the desired re sults. J. - PPAVIJI EbSPIKATCRS - The Conference Committee was of the unanimous op in ion that "dust elimination must he given primary consideration in solving the sili cosis problem", nevertheless, when known methods of elimination are net applicable or are ineffective, respirators should be provided as "a last resort and fer oc casional exposure only, notation of personnel under these conditions is advisable." The report definitely states that there will always, be places where other methods will he inapplicable and ineffective, and respirators will he required fer doing the work, also than there will he situations where respirators will he the primary means of protecting the workmen. The scope of good use of respirators is consider ably beyond that of occasional exposure. The need of rotating personnel depends on the type of work done and the supervision given the workmen. In some operetirs, respirators Ere as much a part of the workman's equipment as his tools. Certainly, it cannot be expected that a person can wear a respirator for several hours con tinuously - but how many jobs are there that would require a person to keep the res pirator or. continuously for ar. extended period of time. The common practice in the majority cf industrial occupations is that the person is intermittently exposed and is afforded many opportunities for the periodic removal of the respiratory protec tive device. The two general types of respirators which the Committee considered suitable for protection against silica dust are: (a) Air-purifying respirators than filter out the dust particles. (b) Supplied-air respirators in which dust-free air breathed by the worker comes to him from an uncor.taminated outside source. Host respirator manufacturers have submitted their devices for testing and approval by the U. S. Bureau of Kines, and only those which have been approved should he used. (a) Air-Purifyine Types of Respirators - Of the air-purifying cla'ss, the type most commonly used is the mechanical filter respirator for mechanically-generated cust. These respirators rive no protection from gases and v&pors. They generally consist of half facepieces to which are attached an exhaust valve and a filtering mediurr. that removes the cust from the inhaled air; some are equipped with a filter medium that removes paint mists and some fumes. They are light in weight and inex pensive. Filter pads must he changed at certain intervals, depending on the concen tration of dust. Some types restrict the field of vision. The general requirements of a safe and suitable Mechanical filter respirator are (1) adequate protection, (2) reasonable comfort and convenience, (3) an acceptable service life period of protec tion, (4) easy cleaning and sterilization, ana (5) low cost of maintenance in good serviceable condition. Studies of mechanical filtration by fibrous materials made by such agencies as the United States 3ureau of Kines (U. S.Bur. of Hines, Tech. Paper No, 394 (1926) and U.S,Pub.Health 3ull.Iio. 177 (1928)) and the Harvard School of Public Health (Journ. Indust. Kyg. 9,26 (1927)) revealed that filtering efficiency varies with the particle size and the amount of solid particulate matter retained; also that the resistance to air flow varies with the amount of solid particulate matter retained and the rate of air flow. After all, the fundamental basis for judging the suitability of a respi rator is whether or not the amount of dust that is unretained or escapes through the filter under conditions of practical use is below the amount that would be harmful to breathe. This is r.ct related to any percentage efficiency. In order to meet the Bureau of Hines requirements for approval, a respiratqr must satisfactorily remove tPC 0156 6