There are two systems that supply oxygen to the masks that are typically found on an aircraft:
A chemical oxygen generator system is connected to all masks in the compartment. Pulling down on one oxygen mask removes the firing pin of the generator igniting a mixture of sodium chlorate and iron powder, and other chemicals, opening the oxygen supply for all the masks in the compartment.
Oxygen production cannot be shut off once a mask is pulled, and oxygen production typically lasts at least 12-22 minutes.
During the production of oxygen, outside air is “bled off” from the compressor stage of the turbine engines and eventually piped into the passenger areas. At this stage, the compressed air becomes extremely hot and the generator should not be touched.
Thus, before it enters the passenger compartment, it is first allowed to expand and is run through a heat exchanger and air cycle system to cool it off sufficiently. A burning smell may be noted and cause alarm among passengers, but this smell is a normal part of the chemical reaction. This system also can work as a heater, with some of the hot air mixed in with the cooled air to regulate cabin temperature.
Next, a gaseous manifold system, which connects all oxygen masks to a central oxygen supply, usually in the cargo hold area. Pulling down on one oxygen mask starts the oxygen supply for that mask only. The entire system can usually be reset in the cockpit or in some other location in the aircraft.
Airplanes do not use oxygen tanks like in scuba diving as they are too heavy and bulky.
So what’s the chemistry?
Here are the main chemicals in an oxygen chemical generator:
1)Barium Peroxide (BaO2)
It is a fine white powder, and when heated up, gives off oxygen.
2)Sodium Chlorate (NaClO3) – the main oxidant in chemical oxygen generators although there is some of the potassium salt present as well
The reaction is usually catalysed by iron on airplanes.
NaClO3 + 2Fe → O2 + Fe2O3 + NaCl
The above reaction produces heat, which causes decomposition of NaClO3 to produce oxygen
2NaClO3 -> 2NaCl + 3O2
3) Potassium Perchlorate (KClO4)
It also decomposes to give oxygen.
KClO4 -> KCl + 2O2
4) Lead styphnate and tetrazene explosive mixture in the percussion cap
References used:
https://en.wikipedia.org/wiki/Chemical_oxygen_generatorhttps://
www.quora.com/What-is-the-chemical-equation-balanced-equation-for-the-generation-of-oxygen-in-chemical-oxygen-generators-found-on-aeroplanes
http://io9.gizmodo.com/planes-dont-carry-tanks-of-oxygen-so-whats-in-your-em-1697413912
http://www.telegraph.co.uk/travel/travel-truths/truth-about-oxygen-masks-on-planes/
http://www.todayifoundout.com/index.php/2016/04/airline-oxygen-bags-important-even-dont-inflate/