How High Pressure Water Mist Fire Fighting System For Ships Works?

The hyper 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

water mist system

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.

water pump

The MICROFOG 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.

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Operating Procedure:

The system start select switch on the main control panel must always be set to AUTO & MANUAL position for automatic start. (The automatic activation with the fire alarm system is possible only in this mode.)

water mist

Starting:

Automatic Start: Water mist system will be automatically released into the protected area where fire is detected by the fire alarm system (both smoke and flame detectors), and an audible and visible alarm is activated in that protected area.

Manual Start: Water mist system can be started manually from the control panel and from the local points whenever needed, independent of the fire alarm system.

The following conditions must be maintained at all times to ensure hyper mist system is on stand by for operation:

  1. Sufficient water level must be retained in the fresh water tank
  2. Make sure the power supply is available.
  3. The fire alarm system must be in operation.
  4. Drain and test valves must be closed.
  5. The area around the Hyper mist water pump must be clear of any obstructions.

Stopping:

After confirming extinction of a fire, the water mist system can be stopped manually by cancelling the signal from the fire alarm system and pressing the STOP button on the control panel or local point.

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Do you know more points that can be added to this article?

Let’s know in the comments below.

You may also like to read – Water-Mist And Sprinkler Systems On Passenger Ships

20 Comments

  1. It would be interesting to hear how the fire fighting procedures are affected on a vessel that has water mist and not CO2.

  2. There are 3 major company which make hyper mist FFS.
    1) Danfoss(European) 2) Unitor(European) 3) Yamato(Japanese)

    Danfoss : Hypermist FFS. form droplet of similar size.

    Unitor: Xflow Hyper mist FFS. for droplet of two different dia. (Near fire, the droplet are much smaller that the outermost blanket)

    Yamato: Fog FFS, Size of droplet is of about 50micrometer.

  3. Sir very well explained would like to add few points

    Applicable

    Mandatory in passenger ships with GT > 500 and cargo ships with GT >2000, for fire extinguishing in machinery spaces of category A with volume > 500 m3 (IMO MSC/Circ.913).
    .

    Designated freshwater tank low level alarm shall be tried out by manually lowering the float.
    Electric source failure shall be tested by removing fuse from the control panel.

    Line Test by Blowing Air:

    The whole piping system to be blown through with compressed air at a pressure of 7 to 8 bar.
    Check the free passage of air from the nozzles.

  4. Multi-stage Centrifugal pumps are widely used with sprinkler systems because they allow a constantly varying flow rate to be delivered at with relatively simple equipment.

    Piston type positive displacement (PD) pumps are also used for HP system.

  5. do you know that these systems can be used to combat Class C (NFPA) fires as well.

  6. Very crucial is the association with engine rooom ventilation. When the blowers are directed on the path of the water mist area, the oxygen replacement effect does not suffice to extinguish the fire. Also, the droplets are pushed away not falling directly on the concerned piece of equipment. That said, it is very important that when testing the system the engine room ventilation is up and running to observe any effect on the water mist functionality.

  7. What will be requirement of Ingress protection for electrical panels installed directly under water mist system?

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