The term “deluge” means “to overrun with water.” It’s a word associated with great floods in human history. So, it wouldn’t take much of an imagination to envision the purpose of a “deluge gun” in the fire service.
A deluge gun — also known as a fire monitor, master stream or deck gun — is a controllable high-capacity water stream used for manual firefighting or automatic fire protection systems.
Its most observable feature is that it can be aimed at a target.
Deluge guns are often fitted to fireboats, tug boats, and on top of large fire trucks for use in manual firefighting efforts, where they can be used to deliver water or foam from outside the immediate area of the fire.
Most truck-mounted deluge guns can be directed by a single firefighter, compared to a standard fire hose which normally requires several firefighters working as a team.
Deluge guns are also designed to accommodate fire-suppression foam which has been injected in the upstream piping.
Deluge guns are sometimes installed in fixed fire protection systems to protect high hazards, such as aviation hangars and helicopter landing pads. Similarly, facilities with highly flammable material such as oil refineries may have permanently installed deluge guns.
Deluge guns can be automatically positioned for fixed systems, or may have portable designs. The latter option enables a firefighter to set up the gun to apply water to a blaze, before leaving it in place to attend other tasks.
A deluge gun brings with it risks when used in an urban setting. It should never be fired into a building with people inside, as the force could knock down a supporting wall in a structure and crush victims. Also, the steam resulting from the high volume of water could cause a blowout or displace oxygen from an enclosed area, creating a risk of asphyxiation for occupants.