Distinguish from water monitor, which is a type of lizard native to South Asia.
Fixed fire monitor at a plastic manufacturing factory
A deck gun in the foreground puts water through a window while a ladder-mounted master stream in the background directs water through the collapsed roof.
A deluge gun, fire monitor, master stream, water cannon, or deck gun is an aimable controllable high-capacity water jet used for manual firefighting or automatic fire protection systems. Fire monitors are often designed to accommodate foam which has been injected in the upstream piping. Fire monitors are often fitted to fire boats, tug boats, and on top of large fire trucks for use in manual firefighting efforts. Fire monitors are also used in fixed fire protection systems to protect high hazards, such as aviation hangars and helicopter landing pads. Most apparatus-mounted fire monitors can be directed by a single firefighter, compared to a standard fire hose which normally requires several. Fire monitors can also be automatically positioned for fixed systems. They can discharge 2,000 US gallons (7,600 liters) per minute, or more.
Deluge guns are also available in portable designs so a firefighter can set up the gun to apply water to a blaze then leave it in place so the firefighter is free for other tasks. Facilities with highly flammable material such as oil refineries may have permanently installed deluge guns for use in the event of a fire.
A master stream is a fire service term for a water stream of 350 US gallons (1,300 liters) per minute or greater. It is delivered by a master stream device, such as a deck gun, deluge gun, or fire monitor. Master streams are often found at the end of aerial ladders, tele-squirt nozzles, or monitor nozzles. The high amount of required pressure makes them unsuitable for handline use.
A deck gun can be found fitted to fireboats and fire trucks for use in manual firefighting efforts. It can be aimed and operated by one firefighter and is used to deliver water or foam from outside the immediate area of the fire.
A master stream brings with it many risks when used in an urban setting. A master stream 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 expanding from the high volume of water delivered could cause a blowout or displace oxygen from an enclosed area, creating a risk of asphyxiation.
Drawing of a deluge gun with dual nozzles
A Great River Fire Department Engine demonstrating its deluge gun.
The Boston fireboat Firefighter shows off its fire monitors.