A detonator, sometimes called a blasting cap in the US, is a small sensitive device used to provoke a larger, more powerful but relatively insensitive secondary explosive of an explosive device used in commercial mining, excavation, demolition, etc.
Top: small nonel detonator with 2 ms delay for chaining nonel tubes; middle: class B SPD detonator; bottom: class C SPD detonator
Inserting detonators into blocks of C-4 explosive
Detonation is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with speeds in the range of 1 km/sec and differ from deflagrations which have subsonic flame speeds in the range of 1 m/sec. Detonation is an explosion of fuel-air mixture. Compared to deflagration, detonation doesn't need to have an external oxidizer. Oxidizers and fuel mix when deflagration occurs. Detonation is more destructive than deflagrations. In detonation, the flame front travels through the air-fuel faster than sound; while in deflagration, the flame front travels through the air-fuel slower than sound.
Detonation of TNT, and shock wave
A controlled bomb disposal in Iraq, 2006; detonating the bomb causes fire and smoke to propel upward.