There are two general types of primer detonators, each type including both instantaneous and delay action detonators.
Type A has a standard shotgun cartridge head as the primer, which depends upon the blow of the firing pin to fire it. The primer composition, once aflame, ignites the uncompressed black powder in the outer retard carrier (instantaneous action type). The flame is then further transmitted to a small black powder pellet which has been compressed under a weight of 1,000 lb. and from there to a fulminate chlorate detonator. Detonation of the latter brings about explosion of the booster charge.
In the 0.05 second delay action primer detonator, the flame from the primer first ignites a mass of highly compressed black powder in the inner retard carrier (compression about 60,000 lb.). From there the flame is transmitted to the uncompressed black powder in the outer retard carrier, then to the small pellet of black powder (1,000 lb. compression), and finally to the mercury fulminate and tetryl held in the detonator case.
Type B has a solid head type of primer, which also requires a blow from the firing pin for ignition. Type B instantaneous action primer detonator transmits its flame from the primer composition to the black powder pellets in the body of the primer detonator. The flame follows through to one small pellet of powder (600 lb. compression) and thence to the mercury fulminate and tetryl contained in the detonator case.
For the 0.1 second delay action detonator the flame from the primer composition first ignites the black powder pellet contained in the retard carrier (60,000 lb. compression). This pellet requires about 0.1 second burning time. The flame is then transmitted to the black powder pellets, and further to a smaller black powder pellet (600 lb. compression) both contained in the body of the detonator. The final stage is ignition of the mercury fulminate and tetryl contained in the case, which in turn fires the booster charge.
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