Pyrofuses and Bullet Hits

These are small devices fired from a low-voltage electric source. They are similar in size and shape and it is important to know which is which and to ensure that they are used only for their stipulated purposes.

Pyrofuses

Pyrofuses are used to ignite pyrotechnic mixtures and flammable substances.

The ignition effect derives from a small bead of chemical material which flares like a match-head when an electric current is passed through an embedded fuse-wire. This is sufficient to ignite such loose materials as mealed gunpowder or flash powder, but is too short-lived to ignite paper or cloth. For these it is necessary to prime the area around the head of the pyrofuse with gunpowder or to treat the material with an area of flammable spirit.

As well as providing ignition the pyrofuse can be used to burn through nylon threads, which in turn can release heavy objects. Fine nylon lines placed ciose to the head of a pyrofuse will melt instantly, but tougher lines require a priming of gunpowder.

Bullet hits

These are plastic-cased explosive detonators and are usually supplied in full-strength and half-strength grades. They are employed primarily to simulate realistic bullet hits on woodwork, rock faces, bottles and clothing.

Bullet hits discharge small pieces of their tough piastic cases with considerable force, and it is important to ensure that they are suitably shielded when used near actors and studio personnel. Where it is impractical to use rigid shields it is possible to surround the bullet hits with energy-absorbing soft materials such as cloth or plastic foam. Such precautions are usually only necessary when bullet hits are employed on the body.

Circuit test

Where long runs of wire or complicated distributions have several connections it is useful to test the circuits for continuity beforehand. To do this using a standard test meter with an internal battery would be to risk firing the charges. Instead, an approved ohm meter designed for use with explosives must be used.

PYROFUSES AND BULLET HITS