"Fire in the hole" is an expression indicating that an explosive detonation in a confined space is imminent. It originated from American miners, who needed to warn their fellows that a charge had been set.[1] The phrase appears in this sense in American state mining regulations,[2] [3] in military and corporate procedures,[4] [5] and in various mining and military blasting-related print books and narratives,[6] e.g. during bomb disposal or throwing grenades into a confined space.[1]
In common parlance it has become a catchphrase for a warning of the type "Watch out!" or "Heads up!".[1]
NASA has used the term to describe a means of staging a multistage rocket vehicle by igniting the upper stage simultaneously with the ejection of the lower stage, without a usual delay of several seconds. On the Apollo 5 uncrewed flight test of the first Apollo Lunar Module, a "fire in the hole test" used this procedure to simulate a lunar landing abort. Gene Kranz describes the test in his autobiography:[7]
. Gene Kranz. Failure is not an option. Berkley Books. 2001. 0425179877. 215.