Cooking off (or thermally caused firing) is when ammunition from a weapon that is not fired which explodes prematurely due to heat in the surrounding environment. The term is used to refer to the explosion of ammunition not loaded into a weapon, as well as for firing unintentionally of weapons loaded with ammunition because of heating. A quick cook-off is a cause of the ignition of a fire. A slow cook-off is caused by a prolonged thermal event, which is not as intense as fire. A cooked-off round may cause the detonation of nearby rounds. The insensitive munitions are engineered so that they are less vulnerable to accidental firing caused by external heat. An inadvertent design flaw in the early 17th century Swedish leather cannons led to the gun tube to overheat and eventually activating the gunpowder and causing injury to the loaders. If the vessels caught fire as they loaded with muzzle-loading guns cannon could ignite. Examples are the merchantman Earl Fiztwilliam and char-broil gas grill – http://qej.radicalmediala.com/__media__/js/netsoltrademark.php?d=ttlink.com%2Flonnahooke – HMS Queen Charlotte. Crews could fire loaded shells from this location to stop them from burning or getting hot. Cooking off is a characteristic that air-cooled machine guns use to fire their rounds from a closed bolt. In this type of design when the trigger is removed, the weapon feed releases one last round inside the chamber. The cartridge’s chamber is then heated by the residual heat. When the kindling point of the propellant is eventually reached it will burn even though the primer has not been struck and thus ignite the chambered round. The autoignition temperature for modern smokeless powder is around 160-170 degrees Celsius (320-338 degrees F). Contrary what is commonly believed, the machine gun does not “runaway” at a cyclic rate (as as opposed to the”slamfire”). Every chambered round needs to be brought to temperature. The amount of time required to do this depends on the temperature of the chamber and environment, but is usually many seconds, though the intent of the shooter could be very fast. The barrel will be cooling at this point. The ammunition that is cased The case of the cartridge made of metallic protects the propellant from heat chamber heat. Before the propellant inside can be burned, it must first be heated. Cooling: Barrels are liquid-cooled (like radiators in an engine) or changed regularly. Modern infantry machine guns (GPMG or general-purpose machine guns) include a range of quick-change barrels. This permits the barrel to cool and shoot while the gun fires. Open bolt: Modern infantry submachine guns operate from an open bolt. This means that the bolt is held in the rear of gun when trigger is pulled. By pulling the trigger, the bolt and it fires the weapon at the same time. If the operation is properly executed (no delays) cooking off cannot be achieved with this model because a cartridge is not chambered until that the trigger is pulled, and the weapon is fired, so there is nothing in the chamber. Modern assault rifles for infantry fire from a closed bolt, meaning that when firing is complete, there is a round in the barrel’s chamber and the bolt as well as working components are in the forward position that is, closing the breech. The gun is fired by pressing the trigger. If the process is operating normally (no interruptions), a cook-off is possible because the cartridge is placed in the chamber. The chamber is heated so that it can absorb the heat and ignite the propellant. A special formula is required to guarantee a constant muzzle velocity regardless of temperature, in addition to the potential of cooking off propellant heated. Caseless ammunition is free of the case of metal that usually houses the igniter or primer, as well as the powder charge (smokeless) that propels it. The metal case absorbs massive quantities of the wasted firing heat. Ejecting this hot, empty , case removes that heat from the gun. Other methods to reduce heat waste are required in caseless rounds, specifically when firing automatically. Crews in tanks that are damaged or disabled may be exposed to serious dangers because of the heat that is emitted by cooking. Some solutions are to store ammunition under water or insulating ammunition compartments. In tanks such as the M1 Abrams the current method is to equip the compartments with blast-off panels, and then place blast-off panel to send energy to the outside of the tank to avoid”jacking in the box” effect. The threat that aircraft armament is cooking off is a significant hazard in pre-flight operations, particularly for aircraft carriers. In the event of a fuel fire, it can take over the deck of the aircraft quickly and even engulf several aircraft, are the most serious threat. This was one of the major factors that contributed to the 1967 fire disaster aboard the USS Forrestal and the USS Forrestal, as the fire (set off by an accidentally launched Zuni rocket that struck the fuel tanks of an awaiting A-4 Skyhawk) detonated two unguided bombs from the Korean War vintage which had been loaded onto the stricken bomber, breaking the fuel tanks of adjacent aircraft and creating a chain reaction of similarly prepared off bombs. Because of the age and condition of the first two bombs the fire safety personnel did not have the ability to cool them off before they cooked off, something that should have been possible for contemporary weapons with higher temperatures for cook-off. Another type of cook-off is the reason for the 1969 explosion at the USS Enterprise (CVN-65) and subsequent fire. The incident also included an Zuni missile. In the course of this incident, the exhaust from an MD-3A “Huffer” Air Start Unit (ASU) was able to cause overheating of the warhead of a Zuni that was attached to a parked aircraft which caused it to burn off. This caused equipment and procedural changes specifically with respect to ASUs like the Forrestal disaster. Oxford English Dictionary (Online ed.). Oxford English Dictionary (Online Ed.). ).
