Watermist systems are one of the newer methods of fire suppression utilizing water. What differentiates these from standard fire sprinkler systems is the water droplet size and volume of water needed for fire suppression. By breaking the water into smaller droplets, the water has a greater ability to absorb heat quickly. As the water turns to steam instantly upon hitting a flame, there is also the residual effect of some oxygen displacement from the fuel and the general wetting effects on objects that have not become involved in the fire situation. Being able to suppress a fire with very little water, the systems are ideal for critical spaces, flammable liquid spaces, equipment spaces, and even light hazard spaces such as hotels and offices where limiting damage from large volumes of water can offset the added costs associated with the watermist.
These systems can be broken into two major categories of either Single Flow or Twin Flow. Single Flow systems consist of a single piping network feeding special nozzles with a high-pressure stream of water that is pressurized by either pumps or high-pressure nitrogen. Twin Flow systems utilize a separate pipe network for the water at a low pressure and high pressure inert gas. These networks are combined at the nozzle to atomize the water into a stream of fine droplets and inert gas, typically nitrogen. Both types of systems can be supplied water either by a potable continuous source or via pressure tanks holding a finite water supply. Systems are manufactured by many fire equipment providers.
Each system has various pros and cons relating to the following attributes: droplet size, operating pressure, piping types and complexities, nozzle layouts, pumping or pressurizing methods, and listings or approvals for certain applications.