Cooking off
Encyclopedia
Cooking off refers to ammunition
exploding
prematurely due to heat in the surrounding environment. It can also refer to a technique used when throwing grenades to achieve a controlled, predictable explosion.
A fast cook-off is a cook-off caused by fire. A slow cook-off is caused by a sustained thermal event less intense than fire.
A cooked-off round may cause a sympathetic detonation
of adjacent rounds.
leather cannon
s led to the gun tube
overheating which prematurely ignited the gunpowder
, injuring the loader.
After the cooking off of artillery shells in the G5 howitzer
s in the late 1980s, the South African Army
changed commands from "cease fire" to "cease loading". This allowed crews to fire any loaded shells to prevent them from heating up and exploding.
s firing from a closed bolt
. In such a design, when the trigger is released the weapon feed leaves a final round in the chamber. Residual heat conducts through the cartridge case. If the flash point
of the propellant
is eventually reached it will burn even though the primer has not been struck, thus firing the chambered round. Contrary to popular myth, this will not cause the machine gun to "runaway" at cyclic rate of fire (as compared to a Slamfire
) because each chambered round has to first be brought up to temperature, which takes at least ten seconds or longer, and the barrel is cooling during this period.
Cook offs in machine guns are prevented by:
s fire from a closed bolt
, meaning that when ready to fire, there is a round in the chamber of the barrel and the bolt and working parts are in the forward position, closing the breech
. Squeezing the trigger releases the striker or hammer
, firing the cartridge in the chamber. Assuming proper operation (no stoppages) a cook off is possible with this design because a cartridge is kept chambered in the potentially hot chamber, where it can absorb enough heat to cause ignition of its propellant.
eliminates the metal
case that typically holds the primer or igniter and the powder charge (smokeless powder
) that propels the bullet
. The metal case absorbs a large portion of the waste heat of firing. Ejecting this hot, empty case removes that heat from the weapon. With caseless rounds, other means of reducing waste heat are necessary, especially in automatic fire.
s. Attempted solutions include storing ammunition under water and insulating ammunition compartments. The current technique, used in tanks like the M1 Abrams
, is to armor the compartments and provide blow-off panels to channel the force of the explosion to the exterior of the tank and prevent the Jack-in-the-box effect
.
, and holding on to it while momentarily allowing its fuze
to partially burn down. The grenade thus detonates sooner after being thrown, limiting the time for the target(s) to take cover, escape the blast radius, or throw it back.
This method is greatly discouraged among armed forces as the fuze length is unpredictable to a degree, posing a significant threat to the user and any nearby friendly personnel, should detonation occur earlier than expected.
s. Fuel fires, which can spread across the flight deck rapidly and engulf many aircraft, are the most serious risk. This was a significant contributor to the 1967 fire disaster
aboard the , when such a fire (set off by an inadvertently fired Zuni rocket
's striking the fuel tank
s of a waiting A-4 Skyhawk
) detonated two iron bombs of Korean War
vintage which had been loaded onto the stricken bomber, rupturing the fuel tanks of adjacent aircraft and setting off a chain reaction of similarly cooked off bombs.
Ammunition
Ammunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...
exploding
Explosion
An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a "high explosive"...
prematurely due to heat in the surrounding environment. It can also refer to a technique used when throwing grenades to achieve a controlled, predictable explosion.
A fast cook-off is a cook-off caused by fire. A slow cook-off is caused by a sustained thermal event less intense than fire.
A cooked-off round may cause a sympathetic detonation
Sympathetic detonation
A sympathetic detonation , also called flash over, is a detonation, usually unintended, of an explosive charge by a nearby explosion. Sympathetic detonation is caused by a shock wave, or impact of primary or secondary blast fragments.The initiating explosive is called donor explosive, the initiated...
of adjacent rounds.
Artillery
Inherent design flaws in early 17th century SwedishSweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
leather cannon
Leather cannon
A leather cannon, or a leather gun, was an experimental Swedish attempt of constructing a lighter weapon that would bridge the gap between muskets and heavy stationary cannons...
s led to the gun tube
Gun barrel
A gun barrel is the tube, usually metal, through which a controlled explosion or rapid expansion of gases are released in order to propel a projectile out of the end at a high velocity....
overheating which prematurely ignited the gunpowder
Gunpowder
Gunpowder, also known since in the late 19th century as black powder, was the first chemical explosive and the only one known until the mid 1800s. It is a mixture of sulfur, charcoal, and potassium nitrate - with the sulfur and charcoal acting as fuels, while the saltpeter works as an oxidizer...
, injuring the loader.
After the cooking off of artillery shells in the G5 howitzer
G5 howitzer
The G5 is a South African towed howitzer of 155 mm calibre designed with the help of the Canadian scientist Gerald Bull and his company, Space Research Corporation and manufactured by Denel Land Systems.-Production history:...
s in the late 1980s, the South African Army
South African Army
The South African Army is the army of South Africa, first formed after the Union of South Africa was created in 1910.The South African military evolved within the tradition of frontier warfare fought by commando forces, reinforced by the Afrikaners' historical distrust of large standing armies...
changed commands from "cease fire" to "cease loading". This allowed crews to fire any loaded shells to prevent them from heating up and exploding.
Machine guns
Cooking off is a characteristic of certain air-cooled machine gunMachine gun
A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....
s firing from a closed bolt
Bolt (firearm)
A bolt is a mechanical part of a firearm that blocks the rear of the chamber while the propellant burns.In manually-operated firearms, such as bolt-action, lever-action, and pump-action rifles and shotguns, the bolt is held fixed by its locking lugs during firing, forcing all the expanding gas...
. In such a design, when the trigger is released the weapon feed leaves a final round in the chamber. Residual heat conducts through the cartridge case. If the flash point
Flash point
The flash point of a volatile material is the lowest temperature at which it can vaporize to form an ignitable mixture in air. Measuring a flash point requires an ignition source...
of the propellant
Propellant
A propellant is a material that produces pressurized gas that:* can be directed through a nozzle, thereby producing thrust ;...
is eventually reached it will burn even though the primer has not been struck, thus firing the chambered round. Contrary to popular myth, this will not cause the machine gun to "runaway" at cyclic rate of fire (as compared to a Slamfire
Slamfire
A slamfire is a premature, unintended discharge of a firearm that occurs as a round is being loaded into the chamber. Slamfires are most common in military firearms that have a free-floating firing pin, as opposed to a spring-loaded one...
) because each chambered round has to first be brought up to temperature, which takes at least ten seconds or longer, and the barrel is cooling during this period.
Cook offs in machine guns are prevented by:
- Cased ammunitionAmmunitionAmmunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...
: Among its many functions, the metallic cartridge case acts as a heat sinkHeat sinkA heat sink is a term for a component or assembly that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems and the radiator in a car...
protecting the propellantPropellantA propellant is a material that produces pressurized gas that:* can be directed through a nozzle, thereby producing thrust ;...
from chamber heat. The case must first be brought up to temperature before the propellant inside can burn. - Cooling: BarrelsGun barrelA gun barrel is the tube, usually metal, through which a controlled explosion or rapid expansion of gases are released in order to propel a projectile out of the end at a high velocity....
can be liquid-cooledCoolantA coolant is a fluid which flows through a device to prevent its overheating, transferring the heat produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor...
(like a radiatorRadiator (engine cooling)Radiators are used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plant or any similar use of such an engine....
in an automobile engine), or exchanged periodically. Most modern infantry machine guns (GPMG, General Purpose Machine Gun) are issued with two quick change barrels that are swapped out allowing one barrel to cool while the gun fires with the other. - Open boltOpen boltA semi or full automatic firearm is said to fire from an open bolt if, when ready to fire, the bolt and working parts are held to the rear. When the trigger is pulled the bolt goes forward, feeding a round from the magazine into the chamber and firing it...
: Most modern infantryInfantryInfantrymen are soldiers who are specifically trained for the role of fighting on foot to engage the enemy face to face and have historically borne the brunt of the casualties of combat in wars. As the oldest branch of combat arms, they are the backbone of armies...
machine gunMachine gunA machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....
s (and submachine gunSubmachine gunA submachine gun is an automatic carbine, designed to fire pistol cartridges. It combines the automatic fire of a machine gun with the cartridge of a pistol. The submachine gun was invented during World War I , but the apex of its use was during World War II when millions of the weapon type were...
s) fire from an open bolt, meaning the bolt remains to the rear when the trigger is released. Pulling the trigger releases the bolt forward and fires the weapon simultaneously. Assuming proper operation (no stoppages) a cook off is not possible with this design because a cartridge is not chambered until the moment the trigger is pulled and the weapon is fired, thus there is nothing in the chamber. - Effective gunnery: Good gunners fire controlled bursts preventing the weapon from overheating.
Closed bolt
Most modern infantry assault rifleAssault rifle
An assault rifle is a selective fire rifle that uses an intermediate cartridge and a detachable magazine. Assault rifles are the standard infantry weapons in most modern armies...
s fire from a closed bolt
Closed bolt
A semi or full-automatic firearm which is said to fire from a closed bolt is one where, when ready to fire, a round is in the chamber and the bolt and working parts are forward...
, meaning that when ready to fire, there is a round in the chamber of the barrel and the bolt and working parts are in the forward position, closing the breech
Breech-loading weapon
A breech-loading weapon is a firearm in which the cartridge or shell is inserted or loaded into a chamber integral to the rear portion of a barrel....
. Squeezing the trigger releases the striker or hammer
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...
, firing the cartridge in the chamber. Assuming proper operation (no stoppages) a cook off is possible with this design because a cartridge is kept chambered in the potentially hot chamber, where it can absorb enough heat to cause ignition of its propellant.
Caseless ammunition
Caseless ammunitionCaseless ammunition
Caseless ammunition is a type of small arms ammunition that eliminates the cartridge case that typically holds the primer, propellant, and projectile together as a unit...
eliminates the metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
case that typically holds the primer or igniter and the powder charge (smokeless powder
Smokeless powder
Smokeless powder is the name given to a number of propellants used in firearms and artillery which produce negligible smoke when fired, unlike the older gunpowder which they replaced...
) that propels the bullet
Bullet
A bullet is a projectile propelled by a firearm, sling, or air gun. Bullets do not normally contain explosives, but damage the intended target by impact and penetration...
. The metal case absorbs a large portion of the waste heat of firing. Ejecting this hot, empty case removes that heat from the weapon. With caseless rounds, other means of reducing waste heat are necessary, especially in automatic fire.
Tanks
Cooking off is a serious hazard to crews in damaged and disabled tankTank
A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...
s. Attempted solutions include storing ammunition under water and insulating ammunition compartments. The current technique, used in tanks like the M1 Abrams
M1 Abrams
The M1 Abrams is a third-generation main battle tank produced in the United States. It is named after General Creighton Abrams, former Army Chief of Staff and Commander of US military forces in Vietnam from 1968 to 1972. The M1 is a well armed, heavily armored, and highly mobile tank designed for...
, is to armor the compartments and provide blow-off panels to channel the force of the explosion to the exterior of the tank and prevent the Jack-in-the-box effect
Jack-in-the-Box Effect
The Jack-in-the-box effect refers to a specific effect of a catastrophic kill on a tank or other turreted armored vehicle in which an ammunition explosion causes the tank's turret to be violently blown off the chassis and into the air...
.
Hand grenades
Common terminology differs in definition for hand grenades; here, cooking off refers to the act of removing both the safety pin as well as allowing the safety level (spoon) to separate, thus priming the hand grenadeHand grenade
A hand grenade is any small bomb that can be thrown by hand. Hand grenades are classified into three categories, explosive grenades, chemical and gas grenades. Explosive grenades are the most commonly used in modern warfare, and are designed to detonate after impact or after a set amount of time...
, and holding on to it while momentarily allowing its fuze
Fuze
Fuze Beverage, commercially referred to as just Fuze , is a manufacturer of teas and non-carbonated fruit drinks enriched with vitamins. Currently the brand consists of five vitamin-infused lines: Slenderize, Refresh, Tea, Defensify, and Vitalize...
to partially burn down. The grenade thus detonates sooner after being thrown, limiting the time for the target(s) to take cover, escape the blast radius, or throw it back.
This method is greatly discouraged among armed forces as the fuze length is unpredictable to a degree, posing a significant threat to the user and any nearby friendly personnel, should detonation occur earlier than expected.
Missiles and air-dropped bombs
The risk of aircraft armament cooking off is a significant hazard during pre-flight operations, especially for aircraft carrierAircraft carrier
An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...
s. Fuel fires, which can spread across the flight deck rapidly and engulf many aircraft, are the most serious risk. This was a significant contributor to the 1967 fire disaster
1967 USS Forrestal fire
The 1967 USS Forrestal fire was a devastating fire and series of chain-reaction explosions on 29 July 1967 that killed 134 sailors and injured 161 on the aircraft carrier , after an unusual electrical anomaly discharged a Zuni rocket on the flight deck...
aboard the , when such a fire (set off by an inadvertently fired Zuni rocket
Zuni (rocket)
The Zuni is a unguided rocket deployed by the United States armed forces. The rocket was developed for both air-to-air and air-to-ground operations. It can be used to carry various types of warheads, including chaff for countermeasures. It is usually fired from the LAU-10 rocket pod holding four...
's striking the fuel tank
Fuel tank
A fuel tank is safe container for flammable fluids. Though any storage tank for fuel may be so called, the term is typically applied to part of an engine system in which the fuel is stored and propelled or released into an engine...
s of a waiting A-4 Skyhawk
A-4 Skyhawk
The Douglas A-4 Skyhawk is a carrier-capable ground-attack aircraft designed for the United States Navy and United States Marine Corps. The delta winged, single-engined Skyhawk was designed and produced by Douglas Aircraft Company, and later McDonnell Douglas. It was originally designated the A4D...
) detonated two iron bombs of Korean War
Korean War
The Korean War was a conventional war between South Korea, supported by the United Nations, and North Korea, supported by the People's Republic of China , with military material aid from the Soviet Union...
vintage which had been loaded onto the stricken bomber, rupturing the fuel tanks of adjacent aircraft and setting off a chain reaction of similarly cooked off bombs.