Chemical oxygen generator
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/* Oxygen candle */
A '''chemical oxygen generator''' is a device that releases [[oxygen]] created by a [[chemical reaction]]. The oxygen source is usually an inorganic [[superoxide]], [[chlorate]] or [[perchlorate]]. A promising group of oxygen sources are [[ozonide]]s. The generators are usually ignited mechanically, by a [[firing pin]], and the chemical reaction is usually [[exothermic]], making the generator a potential [[fire]] hazard. [[Potassium superoxide]] was used as an oxygen source on early manned [[USSR]] [[Outer space|space]] missions, for [[firefighting|firefighters]] and [[mine rescue]].
==Chemical oxygen generator in commercial airliners==
Commercial aircraft provide emergency oxygen to passengers to protect them from drops in cabin pressure. Chemical oxygen generators are not used for the cockpit crew. For each row of seats there are overhead masks and oxygen generators. If a decompression occurs, the panels are opened either by an automatic pressure switch or by a manual switch, and the masks are released. When the passengers pull down on the mask they remove the retaining pins and trigger the production of oxygen.
The oxidizer core is [[sodium chlorate]] ([[Sodium|Na]][[Chlorine|Cl]][[Oxygen|O]]<sub>3</sub>), which is mixed with less than 5
percent [[barium peroxide]] ([[barium|Ba]][[Oxygen|O]]<sub>2</sub>) and less than 1 percent [[potassium perchlorate]] ([[potassium|K]][[chlorine|Cl]][[oxygen|O]]<sub>4</sub>). The explosives in the percussion cap are a [[lead styphnate]] and [[tetracene]] mixture. The chemical reaction is exothermic and the exterior temperature of the canister will reach 260 °C (500°F). It will produce oxygen for 15 to 20 minutes.<ref>{{cite journal
| title = Functions of Barium Peroxide in Sodium Chlorate Chemical Oxygen
| author = Yunchang Zhang, Girish Kshirsagar, and James C. Cannon
| journal = Ind. Eng. Chem. Res.
| volume = 32
| issue = 5
| pages = 966–969
| year = 1993
| url =
| doi = 10.1021/ie00017a028 }}</ref><ref>{{cite journal
| title = Chlorate Candles as a Source of Oxygen
| author = William H. Schechter, R. R. Miller, Robert M. Bovard, C. B. Jackson, and John R. Pappenheimer
| journal = Industrial & Engineering Chemistry
| volume = 42
| issue = 11
| pages = 2348–2353;
| year = 1950
| url =
| doi = 10.1021/ie50491a045 }}</ref> The two-mask generator is approximately 63 mm (2.5") in diameter and 223 mm (8.8") long. The three-mask generator is approximately 70 mm (2.8") in diameter and 250 mm (10") long.
Accidental activation of improperly shipped expired generators caused the [[ValuJet Flight 592]] crash.
==Oxygen candle==
A '''chlorate candle''', or an '''oxygen candle''', is a cylindrical chemical oxygen generator containing a mix of [[sodium chlorate]] and [[iron]] powder. When ignited, the mixture [[smoldering|smolders]] at about 600 °C (1100°F), producing [[sodium chloride]], [[iron oxide]], and about 6.5 man-hours of oxygen per kilogram of the mixture. It releases oxygen at a fixed rate. The mixture has an indefinite shelf life if stored properly; candles stored for 20 years have shown no decrease in oxygen output. The oxygen is released by thermal decomposition. The heat is supplied by the burning iron. The candle has to be wrapped in thermal insulation to maintain the reaction temperature and to protect surrounding equipment.
[[potassium chlorate|Potassium]] and [[lithium chlorate]], and [[sodium perchlorate|sodium]], [[potassium perchlorate|potassium]] and [[lithium perchlorate]]s can also be used in oxygen candles.
It is thought that an explosion caused by one of these candles led to the deaths of two Royal Navy sailors on [[HMS Tireless (S88)|HMS Tireless]], a nuclear-powered submarine, under the Arctic in March 2007<ref>[http://www.theregister.co.uk/2007/03/22/sub_blast_oxy_candle/ 'Oxygen candle' caused explosion]</ref>, during the filming of [[Stargate: Continuum]].
===Solid oxygen generator from Mir===
The TGK generator contains a replaceable cartridge, a thin walled steel tube with a three-part block of oxygen-releasing mixture based on [[lithium perchlorate]]. Two parts are tablets of the chemical mixture and the third one is the igniter tablet with a flash igniter. The igniter is struck by a firing pin when the device is activated. One cartridge releases 600 liters (159 gallons) of oxygen and burns for 5-20 minutes at 450-500 °C. (840-930°F)<ref>[http://www.molecularproducts.com/products_detail.php?id=2 Oxygen Generators]</ref> The oxygen is cooled and filtered from dust and odors, and released into the space station atmosphere.
On [[23 February]] [[1997]], during the exchange of an air filter, a failed chemical oxygen generator spewed a torch-like jet of a molten metal and sparks across one of the [[Mir]] [[space station]] modules, burning for 14 minutes and blocking the escape route to one of the [[Soyuz spacecraft]]. The accident was caused by a leak of the lithium perchlorate from one of the canisters.
==Uses==
Chemical oxygen generators are used in [[aircraft]], breathing apparatus for [[firefighter]]s and mine rescue crews, [[submarine]]s, and everywhere a compact emergency oxygen generator with long shelf life is needed. They usually contain a device for absorption of [[carbon dioxide]], often a filter filled with [[lithium hydroxide]]; a kilogram of LiOH absorbs about half a kilogram of CO<sub>2</sub>.
[[Self-contained self-rescue device]]s (SCSRs) are used to facilitate escape from [[mining|mines]].
On the [[International Space Station]], chemical oxygen generators are located aboard the [[Elektron (ISS)|Elektron]] module. Each canister can produce enough oxygen for one crewmember for one day.
==References==
<references/>
[[Category:Human spaceflight]]
[[Category:Firefighting equipment]]
[[Category:Submarines]]
[[Category:Oxygen]]
[[de:Sauerstoffkerze]]