Squib (explosive)
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A squib is a small explosive about the size of a firecracker. It is often used to ignite a larger pyrotechnic explosive, such as a rocket engine.
In aviation squibs are used to generate pressurised gas to open valves and operate small mechanical devices on such as ejection seats and to pierce metal diaphrams that are retaining pressurised liquids such as halon and fluorocarbon extinguishants or release compressed nitrogen gas to act as a propellant.
They are also widely used in the special effects industry to simulate a bullet hit by coupling the squib itself with a packet of either fake blood for hits on persons or dust/debris for hits on other objects.
Squibs were originally made from parchment tubes, or the shaft of a feather filled with fine black powder and sealed at the ends with wax. These were inserted into the touch holes of cannon and used to ignite the main propellant charge. Roger Bacon first described the making of squibs in 1248.
A "damp squib" is literally one that fails to go off due to wetting but the term has come into general use to mean anything that fails to meet expectations.