Water Mist Fire Suppression Systems
This chapter addresses the engineering of fixed fire suppression systems that discharge water mist. The term water mist, as currently understood in the fire protection field, relates to fine water sprays with no drops larger than 1.0 mm, or 1000 mm (micrometers or microns) [1, 2] Such sprays are not true mists, however. A mist in the scientific sense consists of drops somewhere on a continuum between aerosol (particles with diameter approximately 5 mm) and fog (droplet diameters ranging between 10 and 100 mm) Particles less than 20 mm in diameter take a long time to settle out and, hence, create what is recognized in both literature and science as a "mist." A water mist as intended for fire protection purposes is a fine water spray consisting of a range of droplet sizes, many of which are in the range of true mist particles and some of which are considerably larger. Water mist nozzles produce sprays that have a higher fraction of very fine droplets, in the range of mist, than is typical of standard sprinklers or water spray nozzles.