A squib is a small explosive device used in a wide range of industries, from special effects to military applications. They resemble tiny sticks of dynamite in appearance and in construction, although with considerably less explosive power. Squibs can be used to generate mechanical force, as well as to provide visual pyrotechnic effects both in movies and in live theatrics. Being an explosive device, a squib releases a considerable amount of energy, and can therefore be used for shattering or propelling many different materials.
A squib generally consists of a small tube filled with an explosive substance, and 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, anywhere from 2 to 15 millimeters in diameter.
Squibs are sometimes confused with electric matches, as well as with detonators. While those are used specifically to trigger larger explosives, squibs are generally used as the main explosive element.
Squibs are widely used in the motion picture special effects industry to simulate bullet impacts. For hits on persons, the squib is coupled with a "blood pack", which is a small bag or balloon filled with fake blood, and sometimes chunks of sponge to simulate shattered bone and tissue. Such combinations are sometimes referred to as "blood squibs". For ricochets off other objects, items such as dust and small rocks or wood splinters are attached to the squib.
Other uses for squibs include situations where gas pressure needs to be generated quickly, in small spaces, while not harming any surrounding persons or mechanical parts. In this form, squibs are called gas generators, and are often used in emergency mechanisms — the most common being to inflate vehicle air bags during an accident.
In military aircraft, squibs are implemented to eject the canopy and ejection seat, to deploy parachutes, and to deploy countermeasures. They are also used in general aviation as a mechanism in automatic fire extinguishers, to pierce seals that retain pressurized extinguishant liquids such as halon, fluorocarbon, or liquid nitrogen (used to prevent fuel explosions).
Squibs were first used to simulate bullet impacts in the 1957 film Run of the Arrow, where for the first time audiences were subjected to a realistic representation of a bullet impacting on an on-camera human being, complete with blood spatter.