Ever heard a railroad flare go off? In case you don't know, a railroad flare is basically a blasting cap modified to strap to a rail. The train runs over it, and the expolsion alerts the engineer to trouble ahead.

A friend's father worked for Chessie Systems, so he got a bunch and we strapped them down to the tracks and threw bricks at them to set them off. I remember feeling the percussive wave go by my head, and I couldn't hear for a while after.