HIGH PRESSURE WATER MIST (HYPER MIST) SYSTEM

January 18, 2016 Marine Study Leave a comment

• 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).
• System introduced as an alternative to the Halon systems (prohibited in 1994) for fire fighting in machinery spaces of category A and cargo pump rooms. This fire extinguishing process is based in 3 mechanisms:
  –  Cooling of the flames
  –  Reduction of the oxygen content by the displacement of the air by the expansion
  of the water vapor
  –  Diminution of the radiating heat
• The pressurized water in contact with the fire vaporizes and it is converted into steam. This process absorbs much energy lowering the temperature of the fire and the pressurized water expands about 1700 times taking the air away from the fire. These systems require a water consumption 6 to 10 times lower than a traditional sprinkler system
• It shall be activated automatically by 2 different types of detectors:
  flame and smoke.

• The requirements for test and approval of these systems are specified in the MSC/Circ.1165:
  – It shall be capable of being activated manually
  – It shall be always ready to function and be capable of supplying water during 30 minutes, to avoid the re-ignition of the fire
  – The systems that operate with a reduced output after and initial discharge, shall be ready again in less than 5 minutes
  – It shall have redundant pumping means and shall have a permanent sea chest
  – The means of control shall be outside the protected spaces
  – It shall be supplied with electric power from the main and emergency generators
  – The capacity of the system shall be based in the largest of the protected areas

The most common areas covered by water mist system in ships:

• Incinerator room
• Auxiliary boiler room
• Auxiliary generators
• Main engine cylinder head platform
• Purifier room
• Inert gas generator room
• Steering gear room

Principles of High Pressure Water Mist System (Hyper Mist)

The Hyper Mist Fire Extinguishing System jets out uniform microfog out of nozzles of special specifications under a pressure as high as about 4 to 10 MPa (about 40 to 100 kgf/cm2). The water particle diameter is about 50 to 200 μm. Making use of water in the form of fine particles improves the fire extinguishing effect and efficiency. Moreover, it makes it possible to apply the system to those objects (oil fire, electric fire, etc.) which were considered conventionarilly difficult to be extinguished with water. With these water particles of 50 to 200 μm sizes, excellent fire extinguishing and suppressing performance has been demonstrated through many experiments.

Further, the hyper mist 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)

Hyper Mist Operating Procedure:

Hyper mist system control switch should be always selected in Auto Mode. However, it can be run as Manual mode too by turning the selector switch from Auto to Manual mode. It shall be activated automatically by 2 different types of detectors:
flame and smoke.

Image Credit: www.yamatoprotec.co.jp

Starting of Hyper Mist System:

In Case of Automatic Start: Hyper Mist system will be automatically started and discharge hyper mist into the protected area where fire is detected by the fire alarm system and both smoke and flame detectors activated together, and an audible and visible alarm is raised in that protected area.

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

Stopping the hyper mist system:

After extinction of a fire, the hyper mist system can be stopped manually by cancelling the fire alarm signal from the fire alarm system by pressing the “Stop” button on the control panel or local control point.

The following conditions must be maintained always to ensure hyper mist system is stand by for operation:

• Sufficient water level must be retained in the designated fresh water tank
• Always the power supply should be available.
• The fire alarm system must be in operation.
• Drain and test valves must be closed and well marked.
• The area around the Hyper mist water pump must be clear of any obstructions.
• A clear operation procedure for manual and auto operation be displayed.

Alarm Test:

• 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.

Source: www.yamatoprotec.co.jp, SOLAS