Fire in the hole

"Fire in the hole" is a standard warning, used in many countries in the world, indicating 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. This phrase is also thought to have originated back in the days of wooden warships where they carried large amounts of gunpowder for their cannons in the hold of the ships. A fire on deck could be dealt with but a fire below deck was almost certainly fatal.

The phrase was subsequently adopted by the United States Army and Marines to give notice that a grenade or satchel charge was being tossed into a bunker, spider hole, or other enclosure. It is not used for all explosions — throwing a grenade in the open is not announced, for example — only those surprisingly close.

This phrase is used extensively on film and TV sets by the special effects department whenever setting off effects charges of any nature (from weapons that fire blanks to a blood squib to huge fireballs). It serves as as a warning to the crew that a loud sound is imminent and as a final warning to stop the shot if there are any problems in any department. As a result the phrase is frequently used in MythBusters due to their extensive work on set as Special Effects technicians.

"Fire in the Hole" is also a name for a drive-through prank in which the prankster orders a cup of soda and then opens it up and throws it back through the drive up window back in on the worker. Sadly, there are many videos of this on YouTube.