Water Mist System: How It Works, Benefits and Use Cases

July 11 2023

Water Mist System: How It Works, Benefits and Use Cases

When it comes to fire protection, traditional sprinkler systems have been used for a long time as the preferred method of containment and suppression. However, in recent years, water mist systems have begun to gain traction due to their superior fire suppression capabilities and versatility.

Let's examine how a water mist system operates, its distinctive characteristics, common use cases, and benefits.

What is a Water Mist System?

A water mist fire suppression system is an advanced special hazard solution that uses small water droplets to control, suppress, or extinguish fires. The system works by discharging high-pressure water through specialized nozzles that atomize the water and create a fine mist. This mist is able to absorb heat and displace oxygen, effectively controlling the spread and intensity of the fire. 

Water mist systems are classified by several characteristics, such as:

  • Operating pressure
  • Size of water droplets
  • Extinguishing agent 
  • Design configuration 

Operating Pressure  

According to NFPA 750, there are three distinct pressure classifications for water mist fire suppression systems: low, intermediate, and high-pressure systems. The higher the pressure, the finer the mist created by the system.

Low-Pressure Systems - Under 175 psi 
Intermediate-Pressure Systems - 175 to 500 psi 
High-Pressure Systems - Over 500 psi 

Size of Water Droplets

The size of water droplets generated by the nozzles is critical to the effectiveness of a water mist fire suppression system. Smaller droplets create a finer mist, which increases the cooling effect on a larger surface area when they come into contact with flames. This helps reduce the spread of fire and limits any potential damage caused by it. 

Additionally, smaller droplets are lighter than larger ones, allowing them to cover more space with less water used in the system. These features make high-pressure systems particularly effective at suppressing fires, as their nozzles generate extremely small droplets that are highly efficient at cooling flames down. 

In order to be classified as a water mist system, water droplets should be less than 1,000 microns. For comparison, traditional fire sprinkler systems produce droplet sizes of around 5,000 microns.  

Here’s a closer look at the droplet sizes produced by different water mist pressures: 

Low-Pressure Systems - Under 1,000 microns (the thickness of a dime) 
Intermediate-Pressure Systems - 300 to 500 microns 
High-Pressure Systems - 50 to 100 microns 

Extinguishing Agent: Single-Fluid or Twin-Fluid

Water mist systems are also classified based on the extinguishing agent used. 

Single-fluid water mist systems use one set of distribution piping and only water as the extinguishing agent. The mist is formed by passing water through a nozzle, creating tiny drops that promote rapid cooling and absorb heat from the environment. This type of system works best in smaller, enclosed areas because the particles may not be able to reach larger areas or travel too far before evaporating. 

Twin-fluid water mist systems use separate piping systems and a combination of water and another extinguishing agent, such as nitrogen or air, to create even smaller droplets. Twin fluid systems are often used for large area coverage and applications where precise control over the fire is necessary. 

Design Configurations

Water mist suppression systems are configured based on individual fire hazards and specific applications. Here are the four most common design approaches. 

Local Application - This configuration uses a small number of nozzles to discharge water mist directly onto a specific hazard or object.

Occupancy Protection Systems - This configuration uses a larger number of automatic nozzles to protect an entire facility or a portion of a facility.

Total Compartment Application - The nozzles in this configuration activate at the same time to provide uniform coverage throughout entire rooms or compartments within a building. They are typically used in high-hazard areas where there is a greater risk of fire, such as server rooms or chemical storage areas.

Zoned Application - This configuration is similar to occupancy protection systems, but they are designed to protect specific zones or areas within a building. This allows for more targeted protection in areas where the risk of fire may be higher while also minimizing the amount of water required to suppress the fire.

Common Use Cases 

Water mist systems can be used in many different types of commercial and industrial facilities since they can effectively control the following types of fires:

  • Class A - Combustible materials (paper, wood, cloth)
  • Class B - Flammable liquid or gas (grease, gasoline, oil)
  • Class C - Electrical equipment (appliances, wiring, power tools)

Water mist systems are commonly used in areas where traditional fire suppression methods, such as sprinklers, may not be effective or may cause excessive water damage, such as in data centers, museums, and historic buildings. 

Here are a few additional examples of where water mist systems are frequently used:

  • Machinery spaces
  • Industrial oil cookers
  • Road and rail tunnels
  • Nuclear power plants 
  • Ship passenger cabins
  • Power generation turbines

Top Benefits of Water Mist Systems

 Water mist systems offer several advantages over traditional sprinkler systems and total-flood CO2 systems. These benefits include:

Lower water usage – Unlike sprinkler systems, water mist systems require much less water (up to 90% less). This can help reduce the impact on local water sources and reduce water damage in the event of a fire.

Safer for building occupants – Water mist systems do not create hazardous byproducts and are less likely to cause injury to humans than other fire suppression methods like CO2 systems. 

Lower total cost of ownership – Water mist systems have superior durability, shorter installation times, lower cleanup costs, and require less frequent inspections than other suppression methods.

Greater Versatility – Water mist systems can be used in various applications and settings, from small rooms to large warehouses.

Ready to Install a Water Mist System? 

Installing a water mist system in your building is an effective way to protect people, property, and assets from fire. Its superior suppression capabilities, decreased water usage, and reduced environmental damage make it an optimal fire protection solution for a wide range of facilities.

Seek out experienced fire protection professionals who can advise you on choosing the right water mist system for your needs. They will assess your building, determine the most cost-effective solution, and ensure your system is adequately maintained and inspected in accordance with NFPA 750. 

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Special Hazard Fire Suppression Systems: A Guide For All Business Environments
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