A chemical oxygen generator is a device that releases
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
via a
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
. The oxygen source is usually an inorganic
superoxide
In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula . The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of the ...
,
chlorate
The chlorate anion has the formula ClO3-. In this case, the chlorine atom is in the +5 oxidation state. "Chlorate" can also refer to chemical compounds containing this anion; chlorates are the salts of chloric acid. "Chlorate", when followed by ...
, or
perchlorate
A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. Per ...
;
ozonide
Ozonide is the polyatomic anion . Cyclic organic compounds formed by the addition of ozone () to an alkene are also called ozonides.
Ionic ozonides
Inorganic ozonides are dark red salts. The anion has the bent shape of the ozone molecule.
Inor ...
s are a promising group of oxygen sources. The generators are usually ignited by a
firing pin
A firing pin or striker is a part of the firing mechanism of a firearm that impacts the primer in the base of a cartridge and causes it to fire. In firearms terminology, a striker is a particular type of firing pin where a compressed spring ...
, and the chemical reaction is usually
exothermic
In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...
, making the generator a potential
fire hazard
Fire safety is the set of practices intended to reduce the destruction caused by fire. Fire safety measures include those that are intended to prevent the ignition of an uncontrolled fire and those that are used to limit the development and eff ...
.
Potassium superoxide
Potassium superoxide is an inorganic compound with the formula KO2. It is a yellow paramagnetic solid that decomposes in moist air. It is a rare example of a stable salt of the superoxide anion. It is used as a scrubber, dehumidifier, and gen ...
was used as an oxygen source on early crewed missions of the
Soviet space program
The Soviet space program (russian: Космическая программа СССР, Kosmicheskaya programma SSSR) was the national space program of the former Union of Soviet Socialist Republics (USSR), active from 1955 until the dissoluti ...
, in
submarine
A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
s for use in emergency situations, for
firefighters
A firefighter is a first responder and rescuer extensively trained in firefighting, primarily to extinguish hazardous fires that threaten life, property, and the environment as well as to rescue people and in some cases or jurisdictions also ...
, and for
mine rescue
Mine rescue or mines rescue is the specialised job of rescuing miners and others who have become trapped or injured in underground mines because of mining accidents, roof falls or floods and disasters such as explosions.
Background
Mining law ...
.
In commercial airliners
![Chemical Oxygen Generator, Cut-away View](https://upload.wikimedia.org/wikipedia/commons/4/40/Chemical_Oxygen_Generator%2C_Cut-away_View.gif)
Commercial aircraft provide
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 compressed oxygen canisters, also known as oxygen bottles. In narrow body airliners, for each row of seats there were overhead
oxygen mask
An oxygen mask provides a method to transfer breathing oxygen gas from a storage tank to the lungs. Oxygen masks may cover only the nose and mouth (oral nasal mask) or the entire face (full-face mask). They may be made of plastic, silicone, or r ...
s and oxygen generators. In some wide-body airliners, such as the
DC-10
The McDonnell Douglas DC-10 is an American trijet wide-body aircraft manufactured by McDonnell Douglas.
The DC-10 was intended to succeed the DC-8 for long-range flights. It first flew on August 29, 1970; it was introduced on August 5, 1971, ...
and
IL-96
The Ilyushin Il-96 (russian: Илью́шин Ил-96) is a Russian quadjet long-haul wide-body airliner designed by Ilyushin in the former Soviet Union and manufactured by the Voronezh Aircraft Production Association in Russia. It is powered by ...
, the canisters and oxygen masks were mounted in the top portion of the seat backs, since the ceiling was 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 were released. When the passengers pulled down on the mask they removed the retaining pins and triggered the production of oxygen.
The oxidizer core is
sodium chlorate
Sodium chlorate is an inorganic compound with the chemical formula Na ClO3. It is a white crystalline powder that is readily soluble in water. It is hygroscopic. It decomposes above 300 °C to release oxygen and leaves sodium chloride. Sever ...
(
Na Cl O3), which is mixed with less than 5
percent
barium peroxide
Barium peroxide is the inorganic compound with the formula Ba O2. This white solid (gray when impure) is one of the most common inorganic peroxides, and it was the first peroxide compound discovered. Being an oxidizer and giving a vivid green c ...
(
Ba O2) and less than 1 percent
potassium perchlorate
Potassium perchlorate is the inorganic salt with the chemical formula K Cl O4. Like other perchlorates, this salt is a strong oxidizer although it usually reacts very slowly with organic substances. This, usually obtained as a colorless, crysta ...
(
K Cl O4). The explosives in the percussion cap are a
lead styphnate
Lead styphnate (lead 2,4,6- trinitroresorcinate, C6HN3O8Pb ), whose name is derived from styphnic acid, is an explosive used as a component in primer and detonator mixtures for less sensitive secondary explosives. Lead styphnate is only slightly ...
and
tetrazene explosive
Tetrazene (1-(5-tetrazolyl)-3-guanyl tetrazene hydrate) is an explosive material used for sensitization of priming compositions. It is a derivative of the compound with the IUPAC nomenclature, IUPAC name tetrazene.
Tetrazene is slightly more im ...
mixture. The chemical reaction is exothermic and the exterior temperature of the canister will reach . It will produce oxygen for 12 to 22 minutes. The two-mask generator is approximately in diameter and long. The three-mask generator is approximately in diameter and long.
Accidental activation of improperly shipped expired generators, mistakenly labeled as empty, caused the
ValuJet Airlines Flight 592
ValuJet Airlines Flight 592 was a regularly scheduled flight from Miami International Airport to Hartsfield–Jackson Atlanta International Airport. On May 11, 1996, the ValuJet Airlines McDonnell Douglas DC-9 operating the route crashed into t ...
crash, killing all on board. 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 canister, 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.
Oxygen candle
A ''chlorate candle'', or an ''oxygen candle'', is a cylindrical chemical oxygen generator that contains a mix of
sodium chlorate
Sodium chlorate is an inorganic compound with the chemical formula Na ClO3. It is a white crystalline powder that is readily soluble in water. It is hygroscopic. It decomposes above 300 °C to release oxygen and leaves sodium chloride. Sever ...
and
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
powder, which when ignited
smolders at about , producing
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
,
iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...
, and 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
Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is req ...
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:
:2 NaClO
3 → 2 NaCl + 3 O
2
Potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
and
lithium chlorate, and
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
,
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
and
lithium perchlorate
Lithium perchlorate is the inorganic compound with the formula LiClO4. This white or colourless crystalline salt is noteworthy for its high solubility in many solvents. It exists both in anhydrous form and as a trihydrate.
Applications Inorga ...
s can also be used in oxygen candles.
An explosion caused by one of these candles killed two Royal Navy sailors on , a nuclear-powered submarine, under the Arctic on 21 March 2007. The candle had become contaminated with hydraulic oil, which caused the mixture to explode rather than burn.
In the
Vika oxygen generator
Vika or TGK is an oxygen generating system for spaceflight. It is a SFOG, or solid-fuel oxygen generator, a kind of chemical oxygen generator. It has been used on the retired Mir space station and the International Space Station. It was originally ...
used on some spacecraft,
lithium perchlorate
Lithium perchlorate is the inorganic compound with the formula LiClO4. This white or colourless crystalline salt is noteworthy for its high solubility in many solvents. It exists both in anhydrous form and as a trihydrate.
Applications Inorga ...
is the source of
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
. At 400 °C, it releases 60% of its weight as
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
:
:LiClO
4 → LiCl + 2 O
2
Pressure swing adsorption (PSA) oxygen generators
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
Pressure swing adsorption (PSA) is a technique used to separate some gas species from a mixture of gases (typically air) under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at nea ...
(PSA) incorporates a material called
molecular sieve
A molecular sieve is a material with pores (very small holes) of uniform size. These pore diameters are similar in size to small molecules, and thus large molecules cannot enter or be adsorbed, while smaller molecules can. As a mixture of molecu ...
for gas separation. In the case of oxygen generation a zeolite-based sieve forces preferential adsorption for nitrogen. 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
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
, breathing apparatus for
firefighter
A firefighter is a first responder and rescuer extensively trained in firefighting, primarily to extinguish hazardous fires that threaten life, property, and the environment as well as to rescue people and in some cases or jurisdictions also ...
s and mine rescue crews,
submarine
A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
s, and everywhere a compact emergency oxygen generator with long shelf life is needed. They usually contain a device for absorption of
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
, sometimes a filter filled with
lithium hydroxide
Lithium hydroxide is an inorganic compound with the formula LiOH. It can exist as anhydrous or hydrated, and both forms are white hygroscopic solids. They are soluble in water and slightly soluble in ethanol. Both are available commercially. While ...
; a kilogram of LiOH absorbs about half a kilogram of CO
2.
*Self-contained oxygen generators (SCOGs) are used in submarines.
*
Self-contained self-rescue device
Self-sustainability and self-sufficiency are overlapping states of being in which a person or organization needs little or no help from, or interaction with, others. Self-sufficiency entails the self being enough (to fulfill needs), and a self-s ...
s (SCSRs) are used to facilitate escape from
mines.
*On the
International Space Station
The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...
, chemical oxygen generators are used as a backup supply. Each canister can produce enough oxygen for one crewmember for one day.
See also
*
Oxygen storage Methods of oxygen storage for subsequent use span many approaches, including high pressures in oxygen tanks, cryogenics, oxygen-rich compounds and reaction mixtures, and chemical compounds that reversibly release oxygen upon heating or pressure cha ...
*
SolidOx (welding)
SolidOx was the brand name for welding equipment produced by Cleanweld Products for do-it-yourself welding enthusiasts
from 1965 until at least the early 1980s; the SOLIDOX name was registered as a trademark in 1968.
SolidOx commonly refers to ...
References
{{DEFAULTSORT:Chemical Oxygen Generator
Human spaceflight
Firefighting equipment
Submarine design
Oxygen
Gas technologies