Watermist Fire Suppression

Watermist nozzle

Watermist Fire Suppression – A Review

The recent rise in the interest and use of watermist fire suppression systems in the UK is due to the many advantages over other fire suppression systems. The advantages of watermist include:

  • No chemicals used
  • No risk of asphyxiation as with gas fire suppression
  • Less damage to property than sprinklers and easier to clean up
  • Environmentally friendly
So what is Watermist?

A watermist system is a fixed fire protection system that discharges a fine spray of small water droplets. The system propels water through a specially designed nozzle, breaking the water up into hundreds of micro droplets which produce the mist.

In the event of a fire, the water droplets will the remove heat and displace oxygen from the affected area, resulting in the fire being extinguished.  The mist lowers the temperature, lessens the radiated heat and reduces the oxygen concentration to the extent that combustion can no longer be maintained.

Sprinkler Systems Vs Watermist Systems

So what are the differences between sprinkler systems and watermist suppression systems?

  • Watermist systems discharge less water than sprinkler systems.
  • Clean up and damage to property is less with watermist suppression because, it uses less water.
  • The average water mist droplet has a total surface area at least 100 times greater than the volume of water from a sprinkler system, meaning more effective suppression.
  • Sprinklers require a large tank or even pumphouse due to the large volume of water they use, whereas you can use a cylinder or small standalone tank for watermist.
  • Water mist enables ‘smoke washing’, whereby the smoke particles attach to the droplets and fall to the floor, eliminating the spread of smoke throughout the building.
  • However, watermist suppression is more effective in compartmentalised situations and may not be suitable for larger areas.
  • Watermist droplets can be blown away by air conditioning or open doors thus, reducing effectiveness.

The major difference however, is that sprinkler systems have standards and approvals for both the components of the system, design and installation. At the moment, watermist suppression systems don’t.

Current Standards

Currently there is no published British Standard for water mist systems or the components. Existing watermist standards such as the National Fire Protection Association (NFPA) 750 Standard on Watermist Fire Protection Systems or International Maritime Organisation (IMO) Standards are not directly applicable to UK land-based applications. A European watermist technical specification (CEN TS 14972) has been published but has not been adopted in the UK as its suitability for UK application is uncertain.

However, two new Drafts for Development have been issued:

  • DD 8489: Fixed fire protection systems – Industrial and commercial watermist systems
  • DD 8458: Fixed fire protection systems – Residential and domestic watermist systems

These haven’t been published as full British Standards as there is currently insufficient technical data to support them. These documents try to define the testing protocols for water mist systems in various different applications, but as yet they don’t cover all watermist scenarios. Tests for further applications should be developed going forward and published in additional sections.

Should you Choose Watermist Fire Suppression?

In the absence of a generalised design and installation standard, the suitability of watermist fire suppression for your building depends on a number of factors such as room size, ventilation and insurer’s requirements. Watermist systems should be considered on a case-by-case basis to determine whether a proposed system will meet the fire protection objectives, which need to be clearly stated by the supplier.

Assured Fire & Security are experts in all types of fire suppression, and can design and install systems suitable for your business. For more information please contact our friendly team on 0845 402 3045. Alternatively you can download our Free Fire Suppression Buyers’ Guide.

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