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maritime DC & PPE Information Center

systems and equipment

Water Mist (WM) System


Water mist is a fire extinguishing agent which replaces Halon 1301 in new ship designs such as the LPD-17, because use of Halon 1301 is restricted by international treaty as an ozone-depleting substance. Water mist for machinery spaces is a total-space fire extinguishing system which discharges high-pressure (approximately 1,000 psi) fresh water as a fine mist from nozzles located in all levels except the bilge. High-pressure water mist is effective at suppressing oil pool fires, oil spray fires and class A fire even if the fire is obstructed from the nozzles. Water mist may not totally extinguish deep-seated class A fires, but will knock-down open flaming to a smoldering state and prevent fire spread of a class A fire. Actuation of the water mist system will automatically shut down ventilation in the affected space, but does not include a 30 second or 60 second actuation time delay needed for ventilation air-flow stoppage with Halon 1301 or HFP systems. Water mist should not create a personnel electric shock hazard from un-damaged energized electrical equipment for at least 5 minutes. Actuation of water mist without a fire present does not require evacuation of personnel without breathing protection. However, the presence of toxic fire gases will require evacuation of personnel without breathing protection even if water mist is operating.

Image of nozzle mist Nozzle selected for US Navy Water Mist Systems

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