Water extinguishers should only be used where they work best, on Class A fires, sometimes called ordinary combustible fires. Paper, wood, fabrics, furniture, indeed most things you’ll have stored in your home or office, will provide the fuel for a Class A fire.
A water fire extinguisher is solid red in colour, unless your premises have invested in designer stainless steel extinguishers for a better look. (These are just as effective as their bright red counterparts, but are not BS EN3 certificated, simply because they are not painted red.) Water untis have a hose and nozzle attached, so you can direct a jet of water at the base of the fire.
How Water Fire Extinguishers Work
Water works in two ways, by both extinguishing the flames and soaking the materials in the fire, cooling them down and preventing them from burning any further. (As any Boy Scout will tell you, wet wood won’t burn!)
Most water fire extinguishers are 13A rated (with 21A being better), as they have a limited fire fighting capacity. They also are heavy to handle, as the standard size contains 9 litres of water and weighs 15kgs.
Why Use Water Extinguishers?
Water extinguishers are simple to use, and their contents are neither harmful to people or damaging to the environment. If one is set off accidentally, all you get is a large puddle of water, so you will often see these in schools (usually secured by anti-tamper seals or covers to keep away prying fingers…).
Water and Electricity
Water conducts electricity, so water fire extinguishers should never be used in a situation where there are exposed live electricity cables, or a danger of wiring becoming exposed during a fire. They are best paired with another that is suitable for use on electrical equipment fires, such as a CO2.
Water Extinguishers and Other Classes of Fires
Water is only suitable for Class A fires, as they can do more harm than good on other classes of fires. For example, in a Class B fire involving flammable liquids, the water will simply spread the burning liquid over a larger area rather than extinguish it. On a Class D fire, the spray action will simply blow the burning metal into a wider area, and probably cause it to spark more in the process.
The efficiency and effectiveness of a humble water fire extinguisher can be radically improved with additives. See our page on water additive fire extinguishers for more details.