Electric blasting caps with delays

A delay blasting cap contains a delay element that acts as an internal fuse. A delay element provides a time delay before the base charge fires ( Figure 29). The leg wires on EB caps are made of either iron or copper. Each leg wire on an EB cap is a different color and all caps in a series have the same two colors of leg wires, which serve as an aid in hooking up. The leg wires enter the EB cap through the open end of the cap. To avoid contamination by foreign material or water, a rubber plug seals the opening so that only the leg wires pass through the plug.

Millisecond delay EB caps are commonly used for surface blasting applications (Figure 29). These delays vary between periods depending on the manufacturer. However, the most common increments are 25 and 50 milliseconds (ms). Long period delays caps are also used and have intervals ranging from a hundred ms to over a half second delay. They provide time for rock movement under tight shooting conditions. They are generally used in tunnel driving, shaft sinking, and underground mining.