“Fire in the hole” is one of the many idiomatic expressions in the English language. Its exact origins are not known, but it likely originated with miners. The phrase was originally used to warn of the impending detonation of mining explosives. It is now employed in any situation where an explosion, particularly one in a closed space, is imminent, and can be used more whimsically in a variety of somewhat similar situations.
Modern mining makes extensive use of high explosives. Miners are originally developed the phrase “fire in the hole” to serve as a warning before they were about to detonate explosive charges. Such a warning would have allowed other miners to clear the area where blasting was about to take place. Other workers using explosives, for demolition or land clearance, use this phrase as well.
The military, particularly the American military, also uses the phrase “fire in the hole”. The phrase can be employed whenever explosives are about to go off. This will most frequently be the case when a soldier has hurled a grenade. Other explosives, such as satchel charges, which are used for battlefield demolition work, could also be announced by yelling “Fire in the hole!"
Soldiers usually use this expression only in reference to explosives that they have thrown or launched. A soldier coming under artillery bombardment would not call out “Fire in the hole!” “Incoming!” or some similar exclamation would be used instead.
Military phrases often make their way into civilian life, brought back by soldiers, and then spread through a population more generally if they seem pithy or relevant. The First World War added phrases such as “live and let live” to the English language, along with terms like “trench coat”. “Fire in the hole” has similarly migrated into more common usage.
This phrase is also very popular in action films and video games. These genres are great drivers of popular culture, and have added to the prevalence of the phrase in non-military usage. It could be used when setting off a fireworks display, or a barbeque chef might also use it when lighting a charcoal grill with too much lighter fluid.
“Fire in the hole” and other similar sayings are still used in mining, however. Explosives are just as much a part of modern industrial mining as they were 100 years ago and are just as dangerous. This cry is still used to warn other miners that charges are going to be set off, and that they should seek safety.