Oxygen Generator
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A chemical oxygen generator is a device that releases
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
via a
chemical reaction A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...
. 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 t ...
,
chlorate Chlorate is the common name of the anion, whose chlorine atom is in the +5 oxidation state. The term can also refer to chemical compounds containing this anion, with Chlorate#Compounds (salts), chlorates being the salt (chemistry), salts of chlo ...
, or
perchlorate A perchlorate is a chemical compound containing the perchlorate ion, , the conjugate base of perchloric acid (ionic perchlorate). As counterions, there can be metal cations, quaternary ammonium cations or other ions, for example, nitronium cat ...
.
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. In ...
s are a promising group of oxygen sources, as well. 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 sprin ...
, 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.
Potassium superoxide Potassium superoxide is an inorganic compound with the formula . 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 gene ...
was used as an oxygen source on early crewed missions of the
Soviet space program The Soviet space program () was the state space program of the Soviet Union, active from 1951 until the dissolution of the Soviet Union in 1991. Contrary to its competitors (NASA in the United States, the European Space Agency in Western Euro ...
, in
submarine A submarine (often shortened to sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.) The term "submarine" is also sometimes used historically or infor ...
s for use in emergency situations, for firefighters, 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 la ...
.


In commercial airliners

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 cylinders, also known as oxygen bottles. In narrow body airliners, for each row of seats there were overhead
oxygen mask An oxygen mask is a mask that provides a method to transfer breathing gas, 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 ma ...
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 oxygen generators and oxygen masks are mounted in the top portion of the seat backs, since the ceiling is 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 are released. When the passengers pull 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 5percent
barium peroxide Barium peroxide is an inorganic compound with the formula . 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 colour upo ...
( 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 when the solid is heated at high temperature, although it usually reacts very slowly in solution with reducin ...
( 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 slight ...
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 name tetrazene. Tetrazene is slightly more impact-sensitive th ...
mixture. The chemical reaction is exothermic and the exterior temperature of the generator 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. On May 11, 1996, accidental activation of improperly shipped expired generators, mistakenly labeled as empty "oxy canisters", caused the ValuJet Airlines Flight 592 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 generator, 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; it has symbol Fe () 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, forming much of Earth's o ...
powder, which when ignited smolders at about , producing
sodium chloride Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...
,
iron oxide An iron oxide is a chemical compound composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Ferric oxyhydroxides are a related class of compounds, perhaps the best known of which is rust. Iron ...
, and oxygen at a fixed rate of about 6.5 man-hours 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 of a substance caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic ...
releases the oxygen. The burning iron supplies the heat. The candle must be wrapped in
thermal insulation Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with s ...
to maintain the reaction temperature and to protect surrounding equipment. The key reaction is: :2 NaClO3 → 2 NaCl + 3 O2
Potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...
and lithium chlorate, and
sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
,
potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...
and lithium perchlorates can also be used in oxygen candles. In the Vika oxygen generator used on some spacecraft, lithium perchlorate is the source of
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
. At , it releases 60% of its mass as
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
: :LiClO4 → LiCl + 2 O2


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 ne ...
(PSA) incorporates a
molecular sieve A molecular sieve is a material with pores of uniform size comparable to that of individual molecules, linking the interior of the solid to its exterior. These materials embody the molecular sieve effect, in which molecules larger than the pore ...
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 ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...
, breathing apparatus for
firefighter A firefighter (or fire fighter or fireman) is a first responder trained in specific emergency response such as firefighting, primarily to control and extinguish fires and respond to emergencies such as hazardous material incidents, medical in ...
s and mine rescue crews,
submarine A submarine (often shortened to sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.) The term "submarine" is also sometimes used historically or infor ...
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 is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
, 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 CO2. *Self-contained oxygen generators (SCOGs) are used in submarines. ** They were successfully used by the 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. ** An explosion caused by a so-called oxygen candle 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. *
Self-contained self-rescue device A self-contained self-rescue device, SCSR, self-contained self-rescuer, or air pack is a type of Self-contained breathing apparatus#Closed-circuit, closed-circuit SCBA with a portable oxygen source for providing breathable air when the surround ...
s (SCSRs) are used to facilitate escape from mines. *On the
International Space Station The International Space Station (ISS) is a large space station that was Assembly of the International Space Station, assembled and is maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA (United ...
, chemical oxygen generators are used as a backup supply. Each Vika oxygen generator can produce enough oxygen for one crewmember for one day.


See also

* Oxygen storage * SolidOx (welding)


References

{{DEFAULTSORT:Chemical Oxygen Generator Human spaceflight Firefighting equipment Submarine design Oxygen Gas technologies