The secret behind the efficiency of high pressure water mist are the very small droplets developed by the high pressure. The rate of evaporation increases with the reduced size of the droplets. The evaporation process absorbs heat and provides efficient cooling. Furthermore, the water vapour will deplete the oxygen content inside the fire itself (but not in the space in general).
In machinery spaces the major benefit of water mist is that it is harmless to people. The system can be activated the second a fire is detected, without any need to first evacuate people. Neither is there any need to shut off vents or close openings before evacuation, as the water mist will not escape the space, as gases do. This possibility for immediate activation means that the fire damage is kept at a minimum.
Once the fire has been extinguished, typically within a few minutes after the fire was detected, the water mist will quickly cool down the space and thus prevent re-ignition. The system will not be depleted upon activation, but is always ready for the next activation. Thus there is no interruption of operation.
A common water mist application on offshore platforms is the gas turbine enclosure. Special high-pressure water mist systems have been developed to minimise the thermal shock on the high-tolerance rotor blades, caused by the water hitting the turbine mantle. The system can be connected to a common water mist system on the platform or be equipped with its own self-contained power pack.
The use of high-pressure water mist is not restricted to machinery spaces. As water mist attacks two of the three elements of the so-called ‘fire triangle’, ie the heat and oxygen, it is efficient on virtually any fire. Thus the system can be installed to protect the accommodation, storage and machinery spaces on a platform. With one single system protecting the complete platform, major savings in material and installation costs can be achieved.
The last few years have seen the development of the third generation machinery space water mist fire fighting systems, such as Marioff’s HI-FOG MT4. Better understanding of the extinguishing process and extensive R&D have resulted in simpler and less power consuming systems. Before being applied, such systems have to pass rigorous fire and component tests, defined by organisations such as IMO, FM or VdS.
Like most new systems, water mist as a means for fire fighting was first met with some hesitation. However, full scale testing and actual fires have proven that water mist is a most efficient means for fire fighting, while not featuring the drawbacks of conventional systems. Therefore, history has shown that users who have opted for water mist usually come back as repeat customers.

Stefan Gordin is Vice President, Marioff Corporation OY, Vantaa, Finland. www.marioff.com