Water Mist System vs Sprinkler System
Water mist systems often get confused with sprinkler systems, however, the two function as very different fire protection systems. Both systems use water in different ways to suppress and extinguish fires.
To better understand water mist technology this blog will explore what water mist systems are, how these systems work, and how water mist systems compare to traditional fire sprinkler systems.
What Is A Water Mist Fire Suppression System?
Fire sprinkler systems and water mist systems contain many similar components and both use water as an extinguishing agent to suppress fires. The key difference between sprinkler systems and water mist systems is the size of the water droplets each system produces.
The NFPA 750 defines water mist as a fine mist spray for which 99% of the total volume of liquid (Dv0.99) is distributed in droplets that are less than 1000 microns (μm) in diameter. This standard further defines 3 categories of water mist systems based on the pressure the distribution system piping is exposed to: low-pressure systems, intermediate-pressure systems, and high-pressure systems.
Low-pressure water mist systems operate with pressures of 12.1 bar (175 psi) or less. Intermediate-pressure water mist systems operate with pressures greater than 12.1 bar (175 psi) but less than 34.5 bar (500 psi). High-pressure water mist systems operate with pressures of 34.5 bar (500 psi) or greater.
How Do Water Mist Fire Suppression Systems Work?
Fire sprinkler systems aim to put out fires primarily by drenching a fire and it’s surrounding fuel sources with water. Water mist fire suppression systems extinguish fires by reducing heat, displacing oxygen, and controlling fuel sources by wetting and cooling the surrounding fuel surfaces.
Water mist technology makes use of special nozzles that release a very fine spray containing small water droplets to form a mist. By breaking the water up into hundreds of micro water droplets, water mist systems create a mist covering a wide surface area that is able to absorb heat and lower temperatures within an enclosure.
When these tiny water droplets meet the hot air released from a fire, they evaporate and turn into steam. Steam can absorb more heat per unit of time than larger water droplets, meaning that it can reduce the temperature of the flames at a faster rate.
Water mist systems also combat the oxygen element that fires require for combustion. Once water droplets evaporate into steam, the steam particles displace the oxygen particles around a fire which disrupts and limits a fire’s oxygen supply.
Water droplets also help to pre-wet and block the transfer of radiant heat to surrounding combustible materials, preventing a fire from spreading and growing. By creating a mist of fine water droplets, water mist systems are able to wet and cool fuel surfaces without causing water damage to equipment and machinery within the vicinity.
Difference Between Water Mist Fire Suppression Systems and Fire Sprinkler Systems
While there may be many similarities between water mist systems and traditional sprinkler systems, there are key differences in how these two systems function to extinguish fires. The main differences are listed in the table below:
| Water Mist Fire Suppression System | Fire Sprinkler System |
|---|---|
| As mentioned earlier, the main differentiating factor between these two systems is the size of the water droplets released. Water mist systems discharge water droplets that are less than 1000 microns (μm) in diameter. | Fire sprinkler systems have no limitation on the droplet sizes discharged. Most sprinkler systems produce significantly larger water droplets, with droplet sizes around 5000 microns in diameter. |
| Water mist fire suppression systems have much lower water consumption rates than fire sprinkler systems. It offers a more water-efficient alternative to sprinkler systems. | Fire sprinkler systems can use up to 90% more water and require larger volume water tanks in comparison to water mist systems. |
| Due to the lower water discharge rates and the evaporation of water particles when exposed to heat energy, water mist systems cause less water damage than sprinkler systems. | Fire sprinkler systems cause more water damage to property and other critical assets. |
| Water mist systems combat all three sides of the fire triangle by absorbing heat, displacing oxygen, and wetting the fuel surface. | Fire sprinkler systems suppress fires primarily by wetting the fuel surface. |
| Water mist systems help reduce smoke levels within an enclosure. The fine droplets produced from water mist systems are able to bind very well with smoke and soot particles to bring them to the ground. | Fire sprinkler systems are less effective against smoke. |
Applications for Water Mist Fire Suppression System
Water mist systems work well to control, suppress, and extinguish many different types of fires, including Class A fires (ordinary combustibles) and Class B fires (flammable liquids). Visit our 5 Different Classes Of Fires blog for more information on the different classifications of fires.
The unique benefits that water mist fire suppression systems deliver make it suitable for use in a number of industries:
Marine & Offshore
By significantly reducing the amount of water required for use, water mist systems help lighten the load ships carry. This adds to the stability and fuel economy of large vessels. Water mist systems provide reliable offshore fire protection for all areas of a vessel such as cabins, corridors, machine rooms, and engine rooms.
Hotels & Commercial Buildings
Water mist fire suppression systems are often used in hotels and commercial buildings as it provides maximum fire protection with minimal water damage in these environments. With very little clean-up needed, downtime and disruption to business activities are kept to a minimum. Water mist systems use small and convenient pipe sizes, making it easy to install or retrofit in hotels and commercial buildings.
Oil & Gas Facilities
Oil and gas processing facilities are high-risk working environments that involve the handling, usage, and storage of various flammable liquids and gases. Water mist systems provide effective fire protection against Class B fires that may occur in these environments. By spraying very fine water droplets, water mist systems create a gas-like mist that extinguishes flammable liquid pool fires.
Power Generation
The rapid cooling and blanketing effect of water mist fire suppression makes it suitable for use in power generation facilities. Water mist systems do not damage generator equipment when discharged, and are often used to provide fire protection in generator rooms, transformer rooms, and cable tunnels.
FST Low-Pressure Water Mist Fire Suppression Systems
Water mist fire suppression systems are very efficient, achieving a similar to better level of performance while consuming less water than fire sprinkler systems. Moreover, water mist systems can cover a wider surface area and cause less collateral damage than sprinkler systems.
FST provides low-pressure water mist fire suppression systems, as well as other gaseous fire suppression systems. Contact us for expert advice on water mist fire suppression systems suited to your unique application needs.
