Fuse (explosives)
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See fuse for the other meanings of the word.
In an explosive device, a fuze or fuse is the part of the device that causes it to function. In common usage, the word fuse is used indiscriminately, but when being specific (and in particular in a military context), fuse is used to mean a simple detonating device, like the cord on a firecracker, while fuze is used to mean a more complicated device, such as a proximity fuze.
The simplest fuse is a length of combustible material which burns from the free end, through a small opening in the casing, and into the explosive charge, where it then ignites the explosive material. Fuses are still found in fireworks, model cannons, antique smoothbore firearms, some improvised explosive devices and many forms of pyrotechnics.
More modern forms of fuze, also often called "detonators" or initiators, include:
- time fuzes detonate after a set time (the simple fuse mentioned above falls into this category, but more modern ones use electronic, mechanical or chemical timers).
- contact detonators explode on impact
- proximity fuzes cause a missile or other munition to explode when it comes within a certain distance of the target. Some prox fuzes utilize radar, sonar, Infrared or television cameras.
- remote detonators use wires or radio waves to remotely command the explosive to function.
- altitude fuzes cause a bomb to explode at a certain altitude above sea level by means of a barometric altimeter
Many weapons have fuze systems to ensure that they do not initiate (go off) before intended. In most cases the munition has to travel some distance before it can detonate. In other cases the bomb, mine or projectile has a fuze that prevents accidental initiation (for example, stopping turning of a small propellor so that the striker-pin cannot touch the detonator even if the weapon is dropped on the ground).
These sort of fuzes operate with aircraft weapons where the weapon may have to be dropped over friendly territory to allow a damaged aircraft to continue to fly. The crew can choose to jettison the weapons safe by dropping the devices with fuzes still attached, or drop them live by retaining the fuzes as the weapons leave the aircraft.
Aerial bombs and depth charges can be nose and tail fuzed using different detonator/initiator characteristics so that the crew can choose which effect (fuze) will suit target conditions that may not have been known before the flight. The arming-switch is set to one of safe, nose or tail at the crew's choice.
There are also other fuzing systems.