The water mist fixed fire fighting system is (in my opinion) one of the most significant advancements in shipboard firefighting technologies in the last 20-30 years. Instead of using a toxic gas such as Halon or CO2, water mist systems fill protected spaces with an ultra fine mist of water (either fresh or salt) to remove the heat and ultimately extinguish the fire.
The following video was filmed in the purifier room of a large ship during the initial testing of a newly installed water mist system. Note how quickly the room was filled with a highly concentrated cloud of ultra fine “fire killing” water mist.
While conventional Halon and CO2 systems are very effective in fighting a variety of shipboard fires, they are extremely dangerous (toxic fumes) and typically require a full muster to be taken of all personnel on board the ship. You don’t want to flood a space with toxic gases unless you are absolutely sure there is no chance a person might be in that space. Ultimately, this is a call the master or person in charge may be forced to make.
Additionally, most ships only have enough extinguishing agent on board (CO2 or Halon) for one or two discharges into the larger protected spaces on board a ship (engine rooms, switchgear rooms, machinery spaces, etc.).
With a fixed water mist system, not only can you activate the system immediately without the need for a muster , you always have a virtually unlimited supply of water to keep the system active until the flames are extinguished.
Fixed water mist systems are not cheap and can range from $250,000 on up depending on the scope of the installation. These systems are now mandatory for passenger vessels and all new cargo vessels and will probably become mandatory on even more vessels in the near future.