Water mist extinguishers spray de-ionised water as a very fine mist – think of a fog rather than a water spray. They tackle several types of fire with nothing but water, and leave very little mess.

How They Work

  • The water is de-ionised (purified) and sprayed through a special nozzle as tiny droplets.
  • The droplets cool the fire quickly, and the steam they make helps starve it of oxygen.
  • On burning cooking oil, the droplets are too fine to sink into the fat, so they don't cause the violent flare-up you'd get from a water jet.

Which Fires Can They Tackle?

This depends on the model, so always check the label. Water mist extinguishers are commonly rated for:

  • Class A – paper, wood, fabric and other solids.
  • Class F – cooking oils and fats (some models).
  • Class B – flammable liquids (some models, usually with a lower rating than foam).

See Fire Classes Explained.

Electrical Equipment

Water mist extinguishers pass the electrical (dielectric) test in BS EN 3-7 – that's what the special nozzle is designed for. It means they're safe if used accidentally on live equipment up to 1000 volts from at least 1 metre away.

The British Standard for extinguisher provision (BS 5306-8:2023) still prefers non-conductive extinguishers, such as carbon dioxide (CO2), for live electrical equipment. So next to electrical intake and distribution boards, a CO2 is still the right choice. See CO2 Fire Extinguishers: Sizes, Uses and When You Really Need One.

Good Points

  • One extinguisher covers several risks.
  • Very little water damage or residue to clean up.
  • Just purified water – nothing harmful to the environment and no fluorine chemicals.

Things to Bear in Mind

  • Frost – most only work down to about +5°C, so they're not suitable for unheated buildings or outdoors.
  • Flammable liquids – if you store a lot, a fluorine-free foam may be a better choice. See Are Foam Fire Extinguishers Banned?.

Servicing

Standard water mist extinguishers need a basic service every year and an extended service (also known as a discharge test) every 5 years. Service-free models, such as the P50 range, are checked by you once a year instead – see Service-Free (P50) Extinguishers Explained.

Worth remembering… your fire risk assessment is what decides what your premises need. This guide is general advice, not a substitute for it.

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