BREASTPLATE ASSEMBLY.- The breast-plate assembly (fig. 6-5) houses the plunger assembly, canister guard and holder, and the handle. The plunger pierces the copper foil seal of the canister when the canister is seated in place. The handle actuates the seating mechanism that positions the canister in its housing. When activated, the canister's chlorate candle provides you with oxygen to breathe. The canister gets very hot, but the canister guard or holder protects you from the heat produced by the canister.

COMBINATION VALVE ASSEMBLY.- The combination valve assembly is shown in figure 6-6. It directs the flow of air through the canister to the breathing bag.

HARNESS AND WAIST STRAPS.- The OBA has two types of straps: harness and waist (fig. 67). The harness straps go over your shoulders and snap into D rings. They support the weight of the OBA. The waist strap goes around your body and helps keep the OBA from swinging away from you.

OBA QUICK-STARTING CANISTER.- The quick-starting canister (fig. 6-8) is painted

Figure 6-5.-Breastplate assembly.

Figure 6-6.-Combination valve assembly.

green. This is the canister that you will use for all evolutions other than training. The training canister is discussed later. Figure 6-9 shows a cutaway view of the canister. The rubber gasket provides an airtight seal when the canister is in the operating position in the OBA. The copper foil seal protects the chemicals from moisture until the canister is ready for use. The chlorate candle, which is built into the canister, produces oxygen for about 5 minutes. You will be able to breathe in the oxygen and exhale it just as if you were not wearing an OBA. The moisture and carbon dioxide from your exhaled breath activate the chemicals in the canister. The chemicals in the canister cleanse your exhaled breath of the moisture and carbon dioxide

Figure 6-7.-Harness and waist strap.

Figure 6-8.-Front view of quick-starting canister for use with Type A-4 oxygen breathing apparatus.

Figure 6-9.-Cross-sectional view of quickstarting canister.

and return the remainer of the air to you as you inhale.

The amount of your exertion will deter-mine how long the canister produces oxygen. The more active you are, the faster the chemicals will be expended. The canister will last longer when you are doing mild work such as investigating shipboard damage. When you are involved in hard work, such as fighting a fire, the canister will last for about 30 minutes. Your normal breathing habits will also effect the length of time the canister will last. When you replace an expended canister with a new canister, do so only in fresh air.