CHEMICAL OXYGEN SYSTEMS

 Chemical Oxygen Systems

Sodium chlorate mixed with appropriate binders and a fuel is formed into a block, called a candle, as shown in Figure 9.9.

When this candle is burned, it releases oxygen. The shape and com­position of the candle determines the oxygen flow rate. An igniter, actuated either electrically or by a spring, starts the candle burning, and as the sodium chlorate decomposes, it produces oxygen by a chemical action that looks something like this:

2 NaClO₂ + HEAT®  2 NaCl + 2O₂

The core of the candle is insulated to retain the heat needed for the chemical action and to prevent the housing from getting too hot, and filters are located at the outlet to prevent any contaminants entering the system.

The long shelf life of unused chemical oxygen generators makes them an ideal source of oxygen for occasional flights where oxygen is needed, and for the emergency oxygen supply for pressurized aircraft where oxygen is required only as a standby in case cabin pressurization is lost.

The emergency oxygen systems for pressurized aircraft have the oxygen generators mounted in either the overhead rack, in seat backs, or in bulkhead panels. The masks are located with these generators and are enclosed, hidden from view by a door that may be opened electrically by one of the flight crew members or automatically by an aneroid valve in the event of cabin depres­surization. When the door opens, the mask drops out where it is easily accessible to the user. At­tached to the mask is a lanyard that, when pulled, releases the lock pin from the flow initiation mechanism, so the striker, shown in Figure 9.10, can hit the igniter and start the candle burning. Once a chemical oxygen candle is ignited, it must burn until it is exhausted.

Figure 9.10: Strike for a chemical oxygen candle. Pulling the lanyard removes the safety pin and al­lows the spring to drive the striker down onto the flow initiation mechanism.