If you see a wire with a gray or black core, what does this indicate?

A wire with a gray or black core indicates that it is a safety fuse or time fuse. This type of fuse is designed for use in blasting operations and is specifically engineered to safely initiate explosives. The gray or black color of the wire core is a distinguishing feature that helps users identify it as a time fuse, which functions by allowing a specific delay before igniting an explosive charge. Understanding this identification is crucial for ensuring proper safety protocols are followed in demolition or blasting contexts.

In contrast, the other options refer to different types of explosive initiation systems. Flash powder typically involves a quick combustion and does not use core colors in the same way. Detonating cord is generally a flexible cord filled with high-explosive material, which does not typically have a specific colored core to indicate its function. Electric blasting caps utilize electric current to initiate an explosion and are distinguishable by their own specific characteristics. Each of these options serves a unique purpose in explosive handling which is important for safety and operational efficiency.