In an explosive device, a fuse (or fuze) 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 pyrotechnic 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.
Fuse can be created using a wide variety of technologies.
- Small fireworks usually use a small length of visco fuse, a black powder cored fuse wrapped twice with string and waterproofed, or tissue coated with black powder and rolled to keep the black powder in the center.
- Larger fireworks, some commercial applications, and model cannons usually use a fuse which has a core of grains of black powder, wrapped in a sheath of cloth (usually cotton) fibers and then coated with a laquer, shellac, or more modern protective coating. The core may have a copper wire to strengthen it and to make the flame propagation more reliable, notably in a german 'anzündlitze'-type fuse made by WANO.
- Fuse for blasting (also known as safety fuse), is a larger diameter (typically 1/4 inch or 6.25mm) higher energy, more solidly protected cloth fiber wrapped black powder core fuse. Safety fuse fits into the opening at the end of a pyrotechnic or fuse-ignited blasting cap and is crimped into place. Pyrotechnic blasting caps are still the most common form of detonator used for commercial and military explosives worldwide. Some safety fuse has an outer layer of plastic around the cloth and black powder. This fuse can burn reliably underwater once lit.
- A flying fish fuse 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.
- A falling leaf fuse is an effect fuse like flying fish, but it is slower burning.
- A spolette ('spollette', 'spolette', 'spollete', '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).
Other types of fuse that are used in pyrotechnics:
- Black match
- Quick match