Chemical oxygen generator
Encyclopedia
A chemical oxygen generator is a device releasing oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 created by a chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

. The oxygen source is usually an inorganic superoxide
Superoxide
A superoxide, also known by the obsolete name hyperoxide, is a compound that possesses the superoxide anion with the chemical formula O2−. The systematic name of the anion is dioxide. It is important as the product of the one-electron reduction of dioxygen O2, which occurs widely in nature...

, chlorate
Chlorate
The chlorate anion has the formula ClO. 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 a roman numeral in parentheses, e.g...

, or perchlorate
Perchlorate
Perchlorates are the salts derived from perchloric acid . They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate is also a...

. A promising group of oxygen sources are ozonide
Ozonide
Ozonide is an unstable, reactive polyatomic anion O3−, derived from ozone, or an organic compound similar to organic peroxide formed by a reaction of ozone with an unsaturated compound.-Inorganic ozonides:...

s. The generators are usually ignited mechanically, by a firing pin
Firing pin
A firing pin or striker is part of the firing mechanism used in a firearm or explosive device e.g. an M14 landmine or bomb fuze. Firing pins may take many forms, though the types used in landmines, bombs, grenade fuzes or other single-use devices generally have a sharpened point...

, and the chemical reaction is usually exothermic
Exothermic
In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...

, making the generator a potential fire hazard. Potassium superoxide
Potassium superoxide
Potassium superoxide is the chemical compound with the formula KO2. This rare salt of the superoxide ion is produced by burning molten potassium in pure oxygen...

 was used as an oxygen source on early manned missions of the Soviet space program
Soviet space program
The Soviet space program is the rocketry and space exploration programs conducted by the former Union of Soviet Socialist Republics from the 1930s until its dissolution in 1991...

, for firefighters, and for mine rescue
Mine rescue
Mine rescue is the very specialized job of rescuing miners and others who have become trapped or injured underground in mines because of mining accidents and disasters such as explosions caused by firedamp, roof falls or floods.- Expert volunteers :...

.

In commercial airliners

Commercial aircraft provide emergency oxygen
Emergency oxygen system
Aircraft emergency oxygen systems are emergency equipment fitted to commercial aircraft, intended for use when the cabin pressurisation system has failed and the level of oxygen in the cabin atmosphere drops below a safe level...

 to passengers to protect them from drops in cabin pressure. Chemical oxygen generators are not used for the cockpit crew. In narrow body airliners, for each row of seats there are overhead oxygen mask
Oxygen mask
An oxygen mask provides a method to transfer breathing oxygen gas from a storage tank to the lungs. Oxygen masks may cover the nose and mouth or the entire face...

s and oxygen generators. In wide body airliners, such as the DC-10 and IL-96, the canisters 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 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 chlorate
Sodium chlorate is a chemical compound with the chemical formula . When pure, it is a white crystalline powder that is readily soluble in water. It is hygroscopic. It decomposes above 250 °C to release oxygen and leave sodium chloride...

 (Na
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

Cl
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

3), which is mixed with less than 5
percent barium peroxide
Barium peroxide
Barium peroxide is the chemical compound with the formula BaO2. This grey-white solid is one of the most common inorganic peroxides. Barium peroxide is an oxidizing agent, which is used for bleaching...

 (Ba
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...

O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

2) and less than 1 percent potassium perchlorate
Potassium perchlorate
Potassium perchlorate is the inorganic salt with the chemical formula KClO4. Like other perchlorates, this salt is a strong oxidizer and potentially reacts with many organic substances...

 (K
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

Cl
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

4). The explosives in the percussion cap are a lead styphnate
Lead styphnate
Lead styphnate , whose name is derived from styphnic acid, is an explosive used as a component in primer and detonator mixtures for less sensitive secondary explosives....

 and tetrazene
Tetrazene
Tetrazene is a chemical compound with the molecular formula N4H4. In IUPAC nomenclature, derivatives of this compound are known collectively as tetrazenes. The most common of such derivatives is tetrazene explosive , which is used for sensitization of priming compositions....

 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. The two-mask generator is approximately 63 mm (2.5 in) in diameter and 223 mm (8.8 in) long. The three-mask generator is approximately 70 mm (2.8 in) in diameter and 250 mm (9.8 in) long.

Accidental activation of improperly shipped expired generators caused the ValuJet Flight 592
ValuJet Flight 592
ValuJet Flight 592 was a scheduled domestic passenger flight between Miami International Airport, Miami, Florida, and William B. Hartsfield Atlanta International Airport, Atlanta, Georgia...

 crash. 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 containing a mix of sodium chlorate
Sodium chlorate
Sodium chlorate is a chemical compound with the chemical formula . When pure, it is a white crystalline powder that is readily soluble in water. It is hygroscopic. It decomposes above 250 °C to release oxygen and leave sodium chloride...

 and iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 powder. When ignited, the mixture smolders at about 600 °C (1,112 °F), producing sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...

, iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...

, 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 must be wrapped in thermal insulation to maintain the reaction temperature and to protect surrounding equipment.

Potassium
Potassium chlorate
Potassium chlorate is a compound containing potassium, chlorine and oxygen atoms, with the molecular formula KClO3. In its pure form, it is a white crystalline substance. It is the most common chlorate in industrial use...

 and lithium chlorate
Lithium chlorate
Lithium chlorate is the inorganic chemical compound with the formula LiClO3.Like all chlorates, it is an oxidizer and may become unstable and possibly explosive if mixed with organic materials, reactive metal powders, or sulfur....

, and sodium
Sodium perchlorate
Sodium perchlorate is the inorganic compound with the chemical formula NaClO4. It is the most soluble of the common perchlorate salts. It is a white crystalline, hygroscopic solid that is highly soluble in water and in alcohol...

, potassium
Potassium perchlorate
Potassium perchlorate is the inorganic salt with the chemical formula KClO4. Like other perchlorates, this salt is a strong oxidizer and potentially reacts with many organic substances...

 and lithium perchlorate
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.-Uses:...

s can also be used in oxygen candles.

An explosion caused by one of these candles led to the deaths of two Royal Navy sailors on HMS Tireless
HMS Tireless (S88)
HMS Tireless is a nuclear submarine of the Royal Navy and is the third vessel of her class. She is the second submarine of the Royal Navy to bear this name...

, a nuclear-powered submarine, under the Arctic on March 21, 2007. The candle had become contaminated with hydraulic oil, which caused the mixture to explode rather than burn.

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
Pressure swing adsorption is a technology used to separate some gas species from a mixture of gases under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at near-ambient temperatures and so differs from cryogenic distillation...

 (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. 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
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft 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.Although...

, breathing apparatus for firefighter
Firefighter
Firefighters are rescuers extensively trained primarily to put out hazardous fires that threaten civilian populations and property, to rescue people from car incidents, collapsed and burning buildings and other such situations...

s and mine rescue crews, submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

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
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, often a filter filled with lithium hydroxide
Lithium hydroxide
Lithium hydroxide is an inorganic compound with the formula LiOH. It is a white hygroscopic crystalline material. It is soluble in water and slightly soluble in ethanol...

; a kilogram of LiOH absorbs about half a kilogram of CO2.
  • Self-contained oxygen generators (SCOGs) are used in submarines.
  • Self-contained self-rescue device
    Self-contained self-rescue device
    Self-contained self-rescue device, SCSR, or self-contained self-rescuer, is a portable oxygen source for providing breathable air when the surrounding atmosphere lacks oxygen or is contaminated with toxic gases, eg. carbon monoxide...

    s (SCSRs) are used to facilitate escape from mines
    Mining
    Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

    .
  • On the International Space Station
    International Space Station
    The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...

    , chemical oxygen generators are used. Each canister can produce enough oxygen for one crewmember for one day.
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