Squib (explosive)

A squib is a miniature explosive device used in a wide range of industries and applications, from special effects to the military. It resembles a tiny stick of dynamite, both in appearance and construction, but has considerably less explosive power. A modern squib includes two electrical leads separated by a plug of insulating material; a small bridge wire or electrical resistance heater; and a bead of heat-sensitive chemical composition, in which the bridge wire is embedded. Squibs can generate mechanical force to shatter or propel various materials; they can provide pyrotechnic effects for film and for live theatrics.

A squib generally consists of a small tube filled with an explosive substance, with a detonator running through the length of its core, similar to a stick of dynamite. Also similar to dynamite, the detonator can be a slow-burning fuse, or (as is more common today) a wire connected to a remote electronic trigger. Squibs range in size from ~2 to 15 mm (0.08 to 0.6 in) in diameter.

In the film industry, the term squib often refers to electric matches and detonators used to trigger larger pyrotechnics. They are generally (but not always) the main explosive element in an effect, and are often used in special effects to simulate bullet impacts on inanimate objects or actors. Fake blood packets are typically coupled with squibs and attached to the stage clothes worn by actors, referred to as dead-character costumes, that burst through pre-made "bullet" holes to simulate the appearance of a person being shot and wounded. This creates a realistic and convincing visual effect for movies, TV shows, and stage performances.

Squibs are used in emergency mechanisms where gas pressure needs to be generated quickly in confined spaces, while not harming any surrounding persons or mechanical parts. In this form, squibs may be called gas generators. Two such mechanisms are the inflation of automobile air bags and seat belt pretensioners which sometimes use pyrotechnic devices.

Pyro fuses are also used to disconnect the vehicle's power circuit. The pyro fuse is installed on the positive terminal of the battery and receives a signal from the vehicle's control unit in the event of an accident. During an accident, the pyrotechnic charge in the pyrofuse is triggered, which uses a piston to break the power circuit and de-energize the vehicle's battery.

In 2003, the European Commission adopted Directive 2000/53/EC on end-of-life vehicles (ELV Directive). This measure was introduced to prevent potential fires that may occur due to battery damage during an accident. Battery pyro-fuses ensure instant power disconnection, minimizing the risk of short circuits and fires

Squibs are also used in automatic fire extinguishers, to pierce seals that retain liquids such as halon, fluorocarbon, or liquid nitrogen.

Squibs were originally made from parchment tubes, or from the shaft of a feather, and filled with fine black powder. They were then sealed at the ends with wax. They were sometimes used^[when?] to ignite the main propellant charge in a cannon.