NFPA – 750
Water mist is a versatile and highly efficient firefighting medium. What differentiates water mist from traditional water based systems is its reduced droplet size. When a droplet of water vaporises, it expands by some 1,600 times. As heat absorption is a function of surface area and not volume, smaller droplets mean more surface area and therefore faster heat absorption. Water mist has the unique ability to deliver water as a fine atomised mist. This mist is quickly converted to steam that smothers the fire and prevents further oxygen from reaching it. At the same time, the evaporation creates a significant cooling effect of combustion gases and blocks the transfer of radiant heat. In this way, Watermist combines the fire suppression properties of both conventional water based deluge or sprinkler systems and gaseous fire suppression systems.
However, smaller droplets do not necessarily mean better performance. Droplets must have the necessary momentum to get to the seat of fire where they rapidly cool and expand to deny the fire oxygen.