Water Mist Systems

The water mist system is a relatively new concept. These types of systems were initially developed for use in marine and aircraft applications where weight and space are critical and subsequently have developed to enable protection for hazards such as transformers, oil cooking ranges, and flammable liquids amongst others.

These systems works on the basis of enveloping the risk with fine water droplets to give maximum cooling effect. Water mist system are most effective on “High heat” release fires as the heat converts mist to steam which reduces oxygen levels, so breaking the “Fire Triangle” that is needed for combustion to occur. The mist created gives a considerably larger surface area of water droplets to increase the cooling effect.

The mist is created by discharging water through special nozzles at very high pressure. Nitrogen cylinders used in conjunction with water cylinders, or pump systems are used to deliver water to the nozzles. The mist acts similar to gaseous extinguishing systems in that the mist can extinguish fires in shielded, obstructed locations which would not be reached by other directional water jets / droplets type systems.
 

However, water mist systems can be ineffective in low heat release fires (e.g. waste paper bins fires or smouldering fires) and therefore are not suitable in certain applications. There are also no current prescriptive design standards for water mist systems and therefore the design currently would be based on manufacturer’s tests. Guidance is available on the design of these systems using NFPA 750 and British Standards are in the process of developing a standard.

Further details and other technical data available can be found in the technical section of this web site.