 The oldest and simplest type of cap, fuse caps are a metal cylinder, closed at one end.From the open end inwards, there is first an empty space into which a pyrotechnic fuse is inserted and crimped, then a pyrotechnic ignition mix, a primary explosive, and then the main detonating explosive charge.The primary hazard of pyrotechnic blasting caps is that for proper usage, the fuse must be inserted and then crimped into place by crushing the base of the cap around the fuse.