<P> "Fire in the hole" is a warning that an explosive detonation in a confined space is imminent . It originated with miners, who needed to warn their fellows that a charge had been set . The phrase appears in this sense in state mining regulations, in military and corporate procedures, and in various mining and military blasting - related print books and narratives, e.g., during bomb disposal or throwing grenades into a confined space . </P> <P> In common parlance it has become a catchphrase for a warning of type "Watch out!" or "Heads up!". </P>

Where does the phrase fire in the hole come from