Chemical oxygen generator: Difference between revisions

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{{short description|Device that releases oxygen via a chemical reaction}}

A '''chemical oxygen generator''' is a device that releases [[oxygen]] via a [[chemical reaction]]. The oxygen source is usually an inorganic [[superoxide]],<ref>Hayyan M., Hashim M.A., AlNashef I.M., Superoxide Ion: Generation and Chemical Implications, Chem. Rev., 2016, 116 (5), pp 3029–3085. [[DOI: 10.1021/acs.chemrev.5b00407]]</ref> [[chlorate]], or [[perchlorate]];. [[ozonideOzonide]]s are a promising group of oxygen sources, as well. The generators are usually ignited 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 crewed missions of the [[Soviet space program]], in [[submarine]]s for use in emergency situations, for [[firefighting|firefighters]], and for [[mine rescue]].

== In commercial airliners ==

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[[File:Chemical Oxygen Generator, Cut-away View.gif|thumb|Chemical Oxygen Generator, Cut-away View]]

Commercial aircraft provide [[Emergency oxygen system|emergency oxygen]] to passengers to protect them in case of loss of cabin pressure. Chemical oxygen generators are not used for the cockpit crew, who are typically supplied using [[oxygen cylinder|compressed oxygen canisterscylinders]], also known as oxygen bottles. In narrow body airliners, for each row of seats there were overhead [[oxygen mask]]s and oxygen generators. In some wide-body airliners, such as the [[DC-10]] and [[IL-96]], the canistersoxygen generators and oxygen masks wereare mounted in the top portion of the seat backs, since the ceiling wasis too high above the passengers. If a decompression occurred, the panels were opened either by an automatic pressure switch or by a manual switch, and the masks wereare released. When the passengers pulledpull down on the mask they removed the retaining pins and triggered the production of oxygen.

The oxidizer core is [[sodium chlorate]] ([[Sodium|Na]][[Chlorine|Cl]][[Oxygen|O]]₃), which is mixed with less than 5{{nbsp}}percent [[barium peroxide]] ([[barium|Ba]][[Oxygen|O]]₂) and less than 1 percent [[potassium perchlorate]] ([[potassium|K]][[chlorine|Cl]][[oxygen|O]]₄). The explosives in the percussion cap are a [[lead styphnate]] and [[tetrazene explosive]] mixture. The chemical reaction is exothermic and the exterior temperature of the generator will reach {{convert|260|°C|°F|abbr=on}}. It will produce oxygen for 12 to 22 minutes.<ref>{{cite journal |title=Functions of Barium Peroxide in Sodium Chlorate Chemical Oxygen |author1=Yunchang Zhang |author2=Girish Kshirsagar |author3=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 |author1=William H. Schechter |author2=R. R. Miller |author3=Robert M. Bovard |author4=C. B. Jackson |author5=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 {{convert|63|mm|in|abbr=on}} in diameter and {{convert|223|mm|in|abbr=on}} long. The three-mask generator is approximately {{convert|70|mm|in|abbr=on}} in diameter and {{convert|250|mm|in|abbr=on}} long.

The oxidizer core is [[sodium chlorate]] ([[Sodium|Na]][[Chlorine|Cl]][[Oxygen|O]]₃), which is mixed with less than 5

percent [[barium peroxide]] ([[barium|Ba]][[Oxygen|O]]₂) and less than 1 percent [[potassium perchlorate]] ([[potassium|K]][[chlorine|Cl]][[oxygen|O]]₄). The explosives in the percussion cap are a [[lead styphnate]] and [[tetrazene explosive]] mixture. The chemical reaction is exothermic and the exterior temperature of the canister will reach {{convert|260|°C|°F|abbr=on}}. It will produce oxygen for 12 to 22 minutes.<ref>

{{cite journal

| title = Functions of Barium Peroxide in Sodium Chlorate Chemical Oxygen

|author1=Yunchang Zhang |author2=Girish Kshirsagar |author3=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

|author1=William H. Schechter |author2=R. R. Miller |author3=Robert M. Bovard |author4=C. B. Jackson |author5=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 {{convert|63|mm|in|abbr=on}} in diameter and {{convert|223|mm|in|abbr=on}} long. The three-mask generator is approximately {{convert|70|mm|in|abbr=on}} in diameter and {{convert|250|mm|in|abbr=on}} long.

AccidentalOn May 11, 1996, accidental activation of improperly shipped expired generators, mistakenly labeled as empty "oxy canisters",<ref name=FAA-N904VJ>{{Cite web |title=McDonnell Douglas DC-9-32 {{!}} ValuJet Airlines Flight 592, N904VJ |work=[[Federal Aviation Administration]] |date=19 December 2022 |access-date=10 October 2024 |url=https://www.faa.gov/lessons_learned/transport_airplane/accidents/N904VJ}}</ref> caused the [[ValuJet Airlines Flight 592]] crash, killing all on board.<ref>{{cite episode|series=[[Mayday (Canadian TV series)|Mayday]]|title=Fire in the Hold|season=12|number=2|date=10 August 2012}}</ref> An ATA DC-10, Flight 131, was also destroyed while parked at O'Hare Airport, on August 10, 1986. The cause was the accidental activation of an oxygen canistergenerator, contained in the back of a broken DC-10 seat, being shipped in the cargo compartment to a repair station. There were no fatalities or injuries because the plane contained no passengers when the fire broke out.<ref>{{cite web |title= OT McDonnell Douglas DC-10-40 N184AT |url= https://asn.flightsafety.org/asndb/326951 |work= [[Aviation Safety Network]] |url-status= live |archive-url= https://archive.today/20240621035329/https://asn.flightsafety.org/asndb/326951 |archive-date= June 21, 2024}}</ref><ref>[http://www.airliners.net/photo/American-Trans-Air/McDonnell-Douglas-DC-10-40/0148751/L/&sid=faf57dd90832c5c13834020fb2255dc2 Airliners.net, Photograph, Dave Campbell]</ref>

==Oxygen candle==

A ''chlorate candle'', or an '''oxygen candle''', is a cylindrical chemical oxygen generator that contains a mix of [[sodium chlorate]] and [[iron]] powder, which when ignited [[smoldering|smolders]] at about {{convert|600|°C|°F|abbr=on|sigfig=2}}, producing [[sodium chloride]], [[iron oxide]], and oxygen at a fixed rate of about 6.5 man-hours of oxygen per kilogram of the mixture. The mixture has an indefinite shelf life if stored properly: candles have been stored for 20 years without decreased oxygen output. [[Thermal decomposition]] releases the oxygen. The burning iron supplies the heat. The candle must be wrapped in [[thermal insulation]] to maintain the reaction temperature and to protect surrounding equipment. The key reaction is:<ref name=G&E>{{Greenwood&Earnshaw2nd}}</ref>

:2 NaClO₃ → 2 NaCl + 3 O₂

[[potassium chlorate|Potassium]] and [[lithium chlorate]], and [[sodium perchlorate|sodium]], [[potassium perchlorate|potassium]] and [[lithium perchlorate]]s can also be used in oxygen candles.

In the [[Vika oxygen generator]] used on some spacecraft, [[lithium perchlorate]] is the source of [[oxygen]]. At {{convert|400&nbsp;|°C|°F|abbr=on|sigfig=2}}, it releases 60% of its weightmass as [[oxygen]]:<ref>{{cite journal|title=Lithium Perchlorate Oxygen Candle. Pyrochemical Source of Pure Oxygen|author1=M. M. Markowitz |author2=D. A. Boryta |author3=Harvey Stewart Jr. |journal=Ind. Eng. Chem. Prod. Res. Dev.|year=1964|volume=3|issue=4|pages=321–330

An explosion caused by one of these candles killed two Royal Navy sailors on {{HMS|Tireless|S88}}, a nuclear-powered submarine, under the Arctic on 21&nbsp;March 2007.<ref>{{cite web|last1=Johnson|first1=C. W.|title=Degraded Modes and the 'Culture of Coping' in Military Operations: An Analysis of a Fatal Incident on-board HMS Tireless on 20/21 March 2007|url=http://www.dcs.gla.ac.uk/~johnson/papers/JWSSC2009/Degraded_Modes.pdf}}</ref> The candle had become contaminated with hydraulic oil, which caused the mixture to explode rather than burn.<ref>{{cite web |title = 'Oxygen candle' caused explosion| url = https://www.theregister.co.uk/2007/03/22/sub_blast_oxy_candle/ | publisher = The Register | last = Page | first = Lewis | date = 22 March 2007 | accessdate = 2013-09-04 }}</ref>

In the [[Vika oxygen generator]] used on some spacecraft, [[lithium perchlorate]] is the source of [[oxygen]]. At 400&nbsp;°C, it releases 60% of its weight as [[oxygen]]:<ref>{{cite journal|title=Lithium Perchlorate Oxygen Candle. Pyrochemical Source of Pure Oxygen|author1=M. M. Markowitz |author2=D. A. Boryta |author3=Harvey Stewart Jr. |journal=Ind. Eng. Chem. Prod. Res. Dev.|year=1964|volume=3|issue=4|pages=321–330

|doi=10.1021/i360012a016}}</ref>

:LiClO₄ → LiCl + 2 O₂

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==Pressure swing adsorption (PSA) oxygen generators==

{{Main|Oxygen concentrator}}

Advances in technology have provided industrial oxygen generator systems for use where air is available and a higher concentration of oxygen is desired. [[Pressure swing adsorption]] (PSA) incorporates a material called [[molecular sieve]] for gas separation. In the case of oxygen generation a zeolite-based sieve forces preferential adsorption for nitrogen.{{Citation needed|date=September 2020}} Clean, dry air is passed through the sieve beds on the oxygen generator, producing an oxygen-enriched gas. [[Nitrogen separation membrane]] equipment is also used.

==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]], sometimes a filter filled with [[lithium hydroxide]]; a kilogram of LiOH absorbs about half a kilogram of CO₂.

*Self-contained oxygen generators (SCOGs) are used in submarines.

** They were successfully used by the [[USS New Hampshire (SSN-778)|USS ''New Hampshire'']], an American nuclear-powered submarine, in March 2011 when the submarine suffered an oxygen generator failure while under the [[Arctic ice cap]].<ref>{{cite news| url= https://www.reuters.com/article/us-unitedtechnologies-submarine-idUSTRE72K7U420110321 | work=Reuters | title=Exclusive: UTC-built oxygen generator fails on U.S. submarine | date=21 March 2011 |access-date=21 February 2021 }}</ref>

** An explosion caused by onea ofso-called theseoxygen candlescandle killed two Royal Navy sailors on {{HMS|Tireless|S88}}, a nuclear-powered submarine, under the Arctic on 21&nbsp; March 2007.<ref>{{cite web|last1=Johnson|first1=C. W.|title=Degraded Modes and the 'Culture of Coping' in Military Operations: An Analysis of a Fatal Incident on-board HMS Tireless on 20/21 March 2007|url=http://www.dcs.gla.ac.uk/~johnson/papers/JWSSC2009/Degraded_Modes.pdf}}</ref> The candle had likely become contaminated with hydraulic oil, which would have caused the mixture to explode rather than burn.<ref>{{cite web |title = 'Oxygen candle' caused explosion| url = https://www.theregister.co.uk/2007/03/22/sub_blast_oxy_candle/ | publisher = The Register | last = Page | first = Lewis | date = 22 March 2007 | accessdate = 2013-09-04 }}</ref>{{Failed verification|date=April 2024}}

*[[Self-contained self-rescue device]]s (SCSRs) are used to facilitate escape from [[mining|mines]].

*On the [[International Space Station]], chemical oxygen generators are used as a backup supply. Each canisterVika oxygen generator can produce enough oxygen for one crewmember for one day.<ref>{{cite web|last=Barry|first=Patrick|title=Breathing Easy on the Space Station|url=https://science.nasa.gov/science-news/science-at-nasa/2000/ast13nov_1/|accessdate=9 September 2012|year=2000|publisher=[[National Aeronautics and Space Administration]]|archive-date=11 March 2019|archive-url=https://web.archive.org/web/20190311204439/https://science.nasa.gov/science-news/science-at-nasa/2000/ast13nov_1|url-status=dead}}</ref>

==See also==