When we think of stored oxygen, what we usually think about is large metal tanks holding pressurized oxygen gas. This is the way we see oxygen in hospitals and on welding rigs. We also see SCUBA divers taking their oxygen with them in the form of compressed air in SCUBA tanks. Because they are so common, we tend to think that heavy metal tanks are the only way to store oxygen.
It turns out that there is also a chemical way to store oxygen. Many chemicals, including potassium chlorate (KCl03) and sodium chlorate (NaCl03) are rich in oxygen and are willing to give it up as a nearly pure gas when heated. The SCUBA tanks that divers wear might weigh up to 80 pounds (36 kg) but can store only a few hours of air. An oxygen canister weighing half that can provide about four days worth of oxygen. The sodium chlorate is acting something like an oxygen sponge, and you squeeze the oxygen out with heat.
Modern oxygen canisters are an extremely lightweight way to store oxygen. You find oxygen canisters (also known as chemical oxygen generators) on airplanes, submarines and space stations -- places where oxygen can run out unexpectedly. Typically, an oxygen canister contains a sodium chlorate pellet or cylinder and an igniter. The igniter can be triggered by friction or impact. It generates enough heat to start the sodium chlorate reaction, and then the heat of the reaction sustains itself. The sodium chlorate does not burn -- its decomposition just happens to give off lots of heat and lots of oxygen.
The reason why oxygen canisters can cause fires is because they are hot and they generate oxygen. Anything nearby that happens to ignite will burn intensely because of the rich oxygen supply.
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