45 minutes. For your personnel protection you shouldset the timer on the OBA for 30 minutes, allowing15 minutes to leave the area and return to fresh air.When in operation, the air within the apparatus iscontinuously replenished with oxygen while thechemicals in the canister remove exhaled carbondioxide (CO2) and water vapor. As a result of thischemical action, the OBA wearer may survive and workin a toxic atmosphere, such as a smoke-filledcompartment. With the facepiece and canister in place,using the OBA forms a closed self-sustaining system.For personnel having eyeglasses, a spectacle kit isavailable for the installation of prescription lenses in thefacepiece.WARNINGWhen removing the candle cover, do notremove the cotter pin while pulling the lanyard.Removal of the cotter pin fires the candle andstarts generating oxygen. If that happens whilethe copper foil is intact, internal pressure in thecanister will build up, causing the copper foil orcanister seam to rupture. Do not pull the cotterpin until the canister is inserted in the OBA andthe bail assembly is up and locked.CAUTIONDo not pull the breathing bag tab during normaluse because the oxygen in the bags will leakinto the atmosphere, causing loss of yourbreathing oxygen.WARNINGNever allow grease, oil, or water to enter theneck of the canister. Any of these liquids maycause a violent chemical reaction or explosion.The chemicals contained in the canister areinjurious to skin and equipment.SELF-CONTAINED BREATHINGAPPARATUS (SCBA)The self-contained breathing apparatus (SCBA)(fig. 12-6) is replacing the OBA throughout the Navy.The unit’s main components consist of a harness,high-pressure bottle, pressure regulator, full-face mask,and the high- and low-pressure hoses as shown belowHigh-pressure air cylinders are filled with compressedgrade D breathing air and then stored until needed. Thecylinders themselves are rechargeable, replacing theneed for additional canisters in the OBA system.12-17Student Notes:Figure 12-6.—Self-contained breathing apparatus (SCBA).
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