The difference between water and water additive extinguishers
March 18, 2010barriehol
What are Water Additives in Fire Extinguishers
Chemical additives (like butyldiglycol, pronounced butyl-di-gly-col) when mixed with water increase the effectiveness of a water fire extinguisher by up to 300%. Water additive fire extinguishers, often referred to by the brand name of Hydrospray, are smaller and lighter than standard water fire extinguishers for the same fire rating.
A 3 litre Water additive extinguisher should have the same 13A rating of an ordinary 9 litre water extinguisher. The rating is the maximum volume of combustible materials the extinguisher can manage. It follows that if a 3litre Water Additive has the same 13A rating as 9 litre water it is 3 times as efficient – 300%
A 6 litre water additive will normally have a 21A rating which rather proves that a 6litre with additive has more fire fighting power than a 9 litre water without additive. Many office premises only need a 13A extinguisher which has made the smaller easier to handle 3 and 6 litre more popular.
How Water Additive Fire Extinguishers Work
The additives work by removing water’s natural surface tension, making the water ‘wetter’ or ‘stickier’, so it adheres to and soaks into the burning materials more effectively rather than the water “running off”. Glycols also have a high evaporation temperature so can soak up more heat. There are usually other additives in the mix that enhance performance like alkyl surfactants (soaping agents) that also lower surface tension and are also used in foam extinguishers. It is therefore wrong to say the additives do not improve the fire suppression performance of the water
Spray Nozzle and Electrical risks
The special spray nozzle on water additive extinguishers atomizes the water (and additive) and spreads it in a more effective arc than a conventional jet nozzle. In addition, the nozzle enables safe use in the vicinity of (but not directly on) electrical equipment. What this means is they have passed the 35KV electrical conductivity tests to BSEN3-7:2004. Although Water Fire Extinguishers are not designed to put out electrical fires, with additives they are safe to use near live electrical equipment provided the nozzle is no closer than 1metre. Passing this test needs the combination of the special high pressure atomizing nozzle and the additive. This is also true for many foam extinguishers that also pass this test.
Of course the best advice is to isolate any electrical equipment before tackling the fire, irrespective of the extinguisher being used. Using a light weight 3 litre water additive extinguisher on solid combustible fires is easier than using a heavier 9 litre Water, live electricity or not.