Document O1RwONe48o810D48opv7xQN3X

PERSONAL PROTECTIVE EQUIPMENT Fig. 36-17a. Welder uses air line respi Fig. 36-17b. Diagram shows parts and rator for protection against fumes. connections for air line respirator. The oxygen-generating (rebreathmg) ap paratus consists of a chemical canister, a breathing bag that acts as a reservoir, a facepiece with tube assembly, and a relief valve and check valves to regulate flow in accordance with respiratory requirements The chemical in the canister evolves oxy gen when contacted by the moisture and carbon dioxide in the exhaled breath, and also retains the carbon dioxide and mois ture (moisture retention is important as it permits fog-free lenses) The apparatus is light in weight and contains no intricate parts One model of this type of apparatus is approved by the U S Bureau of Mines for 30 minutes of service life (Fig 36-16c) However, the exothermic reaction that generates oxygen evolves significant heat (the canister surface may reach consider ably above 200 F) which might act as an auto-ignition source to some gases such as carbon disulfide The apparatus produces more oxygen than the user requires, so venting must be done periodically Some models do this automatically but with oth ers it must be done by hand The apparatus and canister should normally be stored at above-freezing temperatures and be com pletely started before being worn and used at subzero temperatures A new canister should be used each tune the apparatus is worn, for it is dangerous to enter a hazardous atmosphere (or even engage in a drill) with a previously opened canister Used canisters should be prompt ly disposed of in accordance with instruc tions printed on them Canisters should be kept away from combustibles so that residu al oxygen will not have a chance to activate them Only copious amounts of clean water should be used to destroy a canister It is important that no one wear selfcontained breathing apparatus unless he is physically fit and well trained Physical fit ness and training are essential because poor physical condition of users and lade of prop er training have been responsible for in juries and deaths After the initial training, men should receive refresher training at least every six months m order to main tain efficiency The facepiece or mouthpiece and nose 38-28