28. BLASTING CAPS.

a. Blastings caps consists, in general, of a copper tube containing a charge of detona-ting explosive, usually tetryl, and a smaller charge of initiating explosive which on initia-tion by an electric current (electric cap) or a flame (nonelectric cap) detonates the lar-ger charge. A current of at least 0.5 ampere each is necessary to insure the detonation of electric caps. (fig. 23).

Figure 23 - Blasting Cap