Definition - What does Water Fog mean?
A “water fog” is a fine spray of water droplets that is produced as a fire-extinguishing agent by certain specialized fire suppression systems.
In a water fog fire suppression system, water is sent through a specialized nozzle at a high speed and pressure, resulting in the production of a fine spray or “fog.” The fast-moving spray instantly turns into vapor upon contact with fire and other high-heat sources, making it an effective method for removing heat from a fire or potential combustion source.
Safeopedia explains Water Fog
Water fog extinguishing systems use less water than traditional water-based extinguishing systems (which rely primarily on volume to extinguish fires), thus making them useful for environments in which there is limited water available. Water fog suppression systems are used for situations in which water-based suppression systems are useful but for whatever reason, traditional water extinguishers are impractical for that case. For example, fog suppression systems may be used to extinguish grease fires or used as a total flooding solution in a work environment in which the use of a CO2 flooding system could pose a threat to worker health. Environments that use fog systems include offshore platforms and large ships, which can use fog systems to suppress spill-based fires without needing to employ a chemical-based fire suppressant that would pose a health risk and require subsequent decontamination activities.
Water fog extinguishers are effective because the surface area to volume ratio of fog water droplets is much larger than the ratio produced by normal water extinguishers, which allows the fog droplets to absorb heat more efficiently. As the droplets vaporize, they expand to approximately 17,000 times their original size. The resulting vapor acts as a barrier over the combusting material, reducing the material's ability to consume oxygen and inhibiting further combustion reactions. The fog’s heat absorption capability also produces a barrier effect that provides workers in the area with some protection from the heat produced by the combustion source.