The LWF Blog

Fire Safety for Facilities Management Personnel – Water Mist Systems – Part 245

March 25, 2024 11:34 am

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 244, LWF discussed water spray systems, in particular medium-velocity spray systems. In part 245, we begin to look at water mist systems.

A standard sprinkler system with conventional sprinkler heads or water spray nozzles produces droplets of a relatively large size to provide momentum capable of penetrating the plume of hot gases rising from the fire.

A system that produces much smaller droplets can, however, allow more efficient extinguishment. The use of fine droplets is usually described as ‘water mist’, where the droplets measure only 10-500 microns. These systems have been popular in recent years partly because of the removal of halon gaseous extinguishing agents from the marketplace for environmental reasons.

A water mist system is able to control, suppress or extinguish a fire by the removal of heat and the displacement of oxygen from the flame reaction zone.

For certain applications, a water mist system can be a suitable alternative to a gaseous suppression system. The water acts as a gas-phase extinguisher and only uses a relatively small amount of water. Despite the relative simplicity, such systems have proven themselves capable of extinguishing large flammable liquid fires.

Water mist systems were used initially to protect machinery spaces on ships, to replace the halon gaseous fire extinguishing systems. The success of water mist in this environment meant that it was natural for more applications to be sought for similar fire hazards on land.

More recently, water mist systems have been used for ‘total compartment’ or ‘volume protection’ systems for the protection of entire enclosures both on land and at sea. For example, water mist may be used in a specific room in a building or on a vessel where the likelihood of a high-heat output flaming fire is much less, but a slowly developing or smouldering fire is a realistic risk. Such fires are more likely in a computer or electronic equipment building.

The success of water mist systems in controlling and suppressing low-heat output fires is less well proven, and it is possible that the performance of the system may be negatively affected by large compartment volume and shielding of a fire by obstacles within the enclosure.

In part 246 of this series, LWF will continue talking about water mist systems. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.

Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 35 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.

 

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.