The water mist or high pressure fog fire fighting system is installed for all important ship’s machinery systems in the engine room (ME. AE, Purifier, Boiler etc.). The high-pressure water mist/fog system provides water mist protection during emergencies to engine room areas and machinery spaces. This system is independent of any other fixed fire fighting system such as foam or CO2 system
Following are the most common areas covered by water mist system:
• Incinerator room
• Auxiliary boiler room
• Auxiliary generators
• Main engine cylinder head platform
• Purifier room
• Inert gas generator room
• Steering gear room
A fresh water pump takes suction from fresh water tank to supply high-pressure water to the sprinkler system. Each area is isolated by valves, which can be opened during emergency situations involving fire. The system is kept at constant stage of readiness.
The Water Mist Fire Extinguishing System has the following effects:
• Cooling effect (quick cooling by evaporation latent heat)
• Oxygen replacement effect (replacement of air with water vapor generated in a large quantity, and absorption of radiation heat)
• Shut-off effect (the floating fog forming walls of water)
• Smoke eliminating effect (the floating smoke particles being adsorbed and settled by the fog)
High-pressure water is injected through a special nozzle working within pressure range of 4 to 10 MPa (depending upon the design of the system), which breaks the water droplets into fine mist. The diameter of the water mist particle range from 50 to 200 μm which improves the fire extinguishing effect and efficiency of the system. The distance between any two nozzles is very critical as area covered by one nozzle must be such that no space is left unsprayed in the fire affected area.
advantages of using water in this form for fire-fighting as compared to the traditional
sprinkler system
• Increased area of coverage and better distribution of the fine water-mist
• Better penetration to the seat of the fire
• Rapid cooling of the seat of the fire and surrounding areas
• Rapid evaporation of the micro-fine droplets to steam helps in smothering the fire (oxygen-starvation).
• Little to no risk of any damage to equipment as water is in the form of a fine mist.
• Lesser consumption of water because of reduced droplet size as compared to the sprinkler.
References
“How High Pressure Water Mist Fire Fighting System For This Works” www.Marineinsight.com
“Vessel water mist fire extinguishing system explained” www.chiefengineerlog.com
“Local Water Mist Fire Extinguishing System Manual Book” TYCO SEAPLUS CO.,LTD
