What is a watermist system?
Watermist is a water spray for which the cumulative volumetric distribution of water droplets is less than 1000 μm (1mm) within the nozzle operating pressure range.
The use of watermist technology to safeguard building inhabitants and assets has gained popularity over the last 30 years. Watermist does this by maximising the efficiency and effectiveness of droplet deployment. The methodology varies depending on both the manufacturer and the application, from the nozzle design, appearance, spacing, activation method, location to orientation.
Definition of a watermist system
An automatic fire suppression distribution system connected to a water supply, that discharges atomised media where required, that is fitted with one or more nozzles capable of delivering watermist intended to control, suppress or extinguish fire.
NFPA 750 is the Standard on Watermist Fire Protection Systems and establishes minimum requirements for water mist technology based on sound engineering principles, test data and field experience. The 2023 edition recognises electronically operated water mist nozzles as a subcategory of automatic water mist nozzles:
3.3.25.2 Electronically-Operated Automatic Water Mist Nozzle. Nozzles that are normally closed and operated by electrical energy that is initiated and supplied by fire detection and control equipment.
NFPA 750 places reliance on the procurement and installation of listed watermist equipment or systems that have demonstrated performance in fire tests as part of a listing process.