Document VJYB8Zjo420X6BVz48VVJmvXo

344 FRANK A. PATTY really offered dependable protection was not made available in the Unite^^| until the United States Bureau of Mines set up approval schedules and prpv'SjflT"* for permissibility tests. These schedules1 are revised from time to time with advances in research and development. It was not until 1935 thatfufV! dust respirators became available to American industry, when the first r*< ' passed the official schedule of tests.. Scores of inferior, and in many useless, devices were discarded after these tests demonstrated their unsatiXfa^ performance. jSwjw These tests now cover oxygen-breathing apparatus, canister gas mllifSSE. masks, abrasive-blasting and other air-line respirators, filter-type dust rcsphjfjpj^ and chemical cartridge respirators. The tests specify the minimum pon'S.,jl|ra performance and the maximum permissible resistance to inhalation and ellSS^ Certificates of approval issued by the Bureau for the accepted devic^^a basis for all lists of approved industrial respiratory protective equipmiJ^fa^ lished by any agency in the United States. No data are published ena/1, public to choose the respirator giving the best performance, but lists oftff: meeting the minimum requirements are published. However, these requTr^^ are raised occasionally to keep pace with the more progressive maiiuf1*' and holders of early approvals are encouraged to improve the perfor their devices to meet these higher standards in order to retain thS| label. Nominal fees charged for approval testing vary with the tirnls for men to perform the scheduled tests. All approved devices are stamp an .appxovaLlabLor-n.umber.rsuch-as-BM--1400i-4n-whieh-the-first the number refer to the schedule of tests under which the device was ap||| the last two are specific for the particular device. .111II. Types and Uses of Respiratory Protective Devices /-\L Respiratory protective devices are used to supplement other .ufigg control and are more frequently used as an emergency measure. 'RcSnjlS protection against all classes and combinations of air contaminants' under two general classifications: (1) air-purifying respirators, which pmur air by removal of the contaminant, and (8) atmosphere-supplying, nesju^ which supply respirable, uncontaminated air or oxygen to the wearer .......... "........ ............... ~~......^............" " A. AIR-PURIFYING RESPIRATORS Air-purifying respirators provide protection only by removing sp'e^j| taminants from the atmosphere. Obviously, sufficient oxygen mui,J! present in the atmosphere to support life. -1 'Self-contained breathing apparatus, U. S. Bur. Mines, Schedule 13G (1946\,*,\Gjj V. S. Bur. Mines, Schedule I4F (1955). Filter-type dust, fume, and mist respirators^ Mines, Schedule 2IA (1955). Supplied-air respirators, V. S. Bur. Mines, Schedule-rlVBjjj) Nonemergency gas respirators, U. S. Bur. Mines, Schedule 23A (1955). RESPIRATORS and respiratory devices 345 1. Gas Masks (Canister Type) 1 r xjkm i||r gas mask Uhlng tube to usually consists of a a,canister containing full facepiece connected by a materials for purifying the air, Itfwith a suitable supporting harness. A check valve in the canister Station valve in the facepiece control the direction of flow of air llevice. The air-purifying materials in the canister vary with the type Since no one substance will remove all contaminants. Alkaline malH' Caustite and soda lime combine with and remove any of the acid nitrogen oxides.; silica gel and activated carbon adsorb organic lUjhia is removed by various materials, such as silica gel adsorbent or Jgvlbstance that has been impregnated with copper or cobalt salts to ISthe ammonia; while carbon monoxide is catalytically oxidised to si- Ulfv pfe by Hopcalite, a trade preparation of manganese and copper oxides. Sbe provided within the canister for removal of particulate matter. wtoa that a canister provides determines its type, and depends upon fjpbth which it is filled. It may be for a single gas, one or more classes ||f'pr all gaseous contaminants. The types of canisters are designated laa a color code, as listed in Table 1. am. TABLE 1 Color Code for Canisters -Gontaminaiits-to*be-proteeted against IF"Acid gases Organic vapors Ammonia Carbon monoxide Dusts, fumes, mists, fogs, and smokes in combination with any of the above gases or vapors Bli Acid gases and organic vapors kv Acid gases, organic vapors, and ammonia AU of the above atmospheric contaminants . . Color White Black Green Blue >/i in. contrasting black or white stripe (on the re spective color) YellowBrown Red jTeOSySeSpiSjiitnfi''iLor.gaEL'masikij^emergency equipment and is not suitable to wear of work, because of discomfort and fatigue due to the ^^wg^oji-pialation and exhalation. This type of respirator is approved for S^t'jl^'uiCratioris of acid gases and organic vapors up to 2 per cent by volume ''Pl'Wn* r .Aceonnft nawmiwmionnniina. The rs>eArHvinicnen lliiffne ro\ff na ncannniifsfftaear depends TuT.pnAoVnl tt'Khje; ggffirSffliMSfi'Sgas encountered, the volume of air inhaled by the wearer, the ^MA^-u^s-'and, amount of the chemical absorbents, and other factors. Ob- ^^l^tuniyi'ersal type of canister must be filled with a variety-of materials- jfet^tuJ^Fotfect.agamst practically all gaseous contaminants. For protection., jgBji1u@eiknown gas, or class of gases, a single-absorbent type of canister is