Water mist systems use highly pressurized water and specialized sprinkler and spray heads to dispense water as small droplets, or mist.
What makes a water mist system different from traditional wet sprinkler systems is the size of the water droplets. NFPA 750 defines low, intermediate, and high-pressure systems. Water mist systems are those with operating pressures of 500 psi or greater.
For a system to be considered water mist, it has to have droplets smaller than 1,000 microns. For reference, most traditional sprinkler systems have droplet sizes around 5,000 microns.
Smaller droplets translate to an increase in the number of droplets that can be dispersed. The more numerous the water droplets, the larger the water surface area exposed to heat. More drops will evaporate and turn to steam that will then absorb more heat.