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In an explosive, pyrotechnic device or military munition, a 'fuse' (or 'fuze') is the part of the device that initiates function. In common usage, the word fuse is used indiscriminately. However, when being specific (and in particular in a military context), the term ''fuse'' describes a simple pyrotechnic detonating device, like the cord on a firecracker, whereas the term ''fuze'' is used to describe a more complicated ignition device incorporating mechanical and/or electronic components eg a proximity fuze for an artillery shell or pencil detonator.

Contents

Burning/Safety fuse

Munition fuzes

See also

External Links

Burning/Safety fuse

The simplest form of fuse is the burning fuse, believed to date back to the 10th century and originating in China, this simple fuse consisted of lightweight paper filled with loose gunpowder, and served as a means of delaying ignition in fireworks. This simple form of burning fuse can still be found today in many modern pyrotechnics. The commercial and military version of a burning fuse is often referred to as a safety fuse. The safety fuse (invented by William Bickford) is a simply length of cord either filled with combustible material, or itself made from combustible material. A safety fuse is often coded by its burn time for 30 cm i.e. 60 seconds, which means that a length of fuse 30 cm long will take 60 seconds to burn.
Modern day safety fuses are often used in mining and military operations, to provide a time-delay before ignition, and they more often than not are used to initiate an explosive detonator, thereby starting an explosive chain reaction to detonate a larger more stable main charge.
Safety fuses are typically colored black to distinguish them from detonating cords such as Primacord, which is brightly colored or transparent.
Fuses are found in fireworks, model cannons, antique smoothbore firearms, some improvised explosive devices and many forms of pyrotechnics.
Burning fuses may take many forms:

★ Some safety fuses have an outer layer of plastic around the cloth and black powder. These fuses can burn reliably underwater once lit, since the explosive provides both its own fuel and oxidant.

★ A slow match is a very slow-burning fuse consisting of a hemp or cotton rope saturated with an oxidizer such as potassium nitrate. Slow matches are used as a source of fire for manually lighting other devices, such as matchlock guns, or fuses on black powder cannons. Before percussion caps, slow matches were most suitable for use around black powder weapons because it could be roughly handled without going out, and only presented a small glowing tip instead of a large flame that risked igniting powder supplies nearby.

★ Today's punks (wood splints covered with ground plant pith saturated with nitrate) used for lighting consumer fireworks are a type of slow match.

★ A Black match is a type of fuse consisting of cotton string coated with a dried slurry of black powder and glue. This acts as a simple pass-fire, and was used to fire ancient cannons. They are used today in fireworks construction.

★ A quick match or piped match is a type of black powder fuse that burns very quickly, some hundreds of feet per second. They consist of black matches covered with a loose paper wrap (pipe). When lit, the flame propagates quickly down the paper pipe from the hot gases produced by the burning powder. Quick matches are used in professional fireworks displays to pass fire nearly instantly between devices that must be physically separated while firing simultaneously, such as a finale rack. Devices which should fire in sequence can be branched from a single master fuse, consisting of quick match spliced onto Visco fuses of various length for time delays.

★ An Ignitor Safety Fuse Electric (ISFE) lights a main fuse or device when activated by an electrical current. They typically consist of a pair of wires leading to a thin resistance wire that heats when current is applied. The resistance wire is covered by a bit of pyrotechnic composition that ignites from the wire heating, providing enough fire to reliably ignite the main fuse via a mechanical connection, or the device directly. Estes model rocket motors are lit by a type of electric match. Large fireworks displays are launched with complex timing sequences using a computer that energizes electric matches connected to the individual device fuses.

★ A flying fish fuse is an unusual type of component for fireworks. It is made like Visco fuse, but contains a metallic spark composition or other effect instead of black powder. Flying fish can thus perform as a main effect instead of just an initiator. For example, simply lighting a short piece of flying fish on the ground makes it fly through the air, seeming to swim in random directions, while emitting sparks and noise. A aerial shell loaded with many such pieces results in a beautiful myriad of pieces flying and sparking high in the air.

★ A 'spoolette' is a delay fuse consisting of a hollow wooden dowel rammed full of black powder. A spoolette is glued into the wall of a fireworks shell and ignited by the lift charge that launches the shell into the air. The spoolette, after a delay that allows the shell to reach its top of trajectory, ignites the shell's main effect(s). The tough wood construction ensures that the fuse burns reliably despite the explosive force and acceleration of the launch.

★ The saucisson was an early form of fuse.

Munition fuzes

Some countries use the z spelling to distinguish between burning fuses and more complicated munition fuzes. Examples of both spellings can be found.
A fuze refers to a device used in munitions which is designed to detonate, or to set forces into action to ignite, detonate or deflagrate, the charge (or primer) under specified conditions.
Types of fuzes include:

★ time fuzes detonate after a set period of time by using mechanical, electronic, igniferious or chemical timers.

★ contact detonators or point detonating fuzes explode on impact.

★ proximity fuzes cause a missile or other munition to explode when it comes within a certain distance of the target. Some proximity fuses utilize radar, sonar, Infrared, photo-electric 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 an infrared rangefinder, radar, or barometric altimeter
Many weapons have fuzing systems to ensure that they do not initiate (explode) prematurely. In most cases the munition has to travel some distance or wait for a period of time before it can detonate.
In modern artillery shells, most fuzes incorporate several safety features to prevent a fuze arming before it leaves the gun barrel. These safety features may include arming on "set-back" or by centrifugal force, and often both operating together. Set-back arming uses the inertia of the accelerating artillery shell to remove a safety feature as the projectile accelerates from rest to its in-flight speed. Rotational arming requires that the artillery shell reach a certain rpm before centrifugal forces cause a safety feature to disengage or move an arming mechanism to its armed position (artillery shells are fired through a rifled barrel, and so spin during flight).
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 sorts of fuze operate with aircraft weapons where the weapon may have to be jetisoned 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 safety pins still attached, or drop them ''live'' by retaining the safety pins 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.
Base fuzes are also used by artillery and tanks for shells of the 'squash head' type. Some types of armour piercing shells have also used base fuzes, as have nuclear artillery shells.
There also exist more complicated integrated fuzing and firing systems, typically used in missiles and special weapons.

See also

★ Percussion cap

★ Proximity fuze

★ Thermalite

External Links

★ Safing, Arming, Fuzing, and Firing (SAFF) info from Globalsecurity.org

★ 90th Infantry Division Preservation Group - page on 81mm Mortar Fuzes