Water mist systems are used for special hazards applications. This type of system is typically used where water damage may be a concern, or where water supplies are limited.  NFPA 750 defines water mist as a water spray with a droplet size of "less than 1000 microns at the minimum operation pressure of the discharge nozzle".  The droplet size can be controlled by adjusting the discharge pressure through a nozzle of a fixed orifice size. The fire suppression mechanisms provided by water mist systems include cooling, local flame oxygen reduction, and radiation blocking.  
In operation, water mist systems can operate with the same functionality as deluge, wet pipe, dry pipe, or pre-action systems. The difference is that a water mist system uses a compressed gas as an atomizing medium, which is pumped through the sprinkler pipe. Instead of compressed gas, some systems use a high-pressure pump to pressurize the water so it atomizes as it exits the sprinkler nozzle. Systems can be applied using local application method or total flooding method, similar to Clean Agent Fire Protection Systems.