Most people know the basics about fire extinguishers. For instance many people know that water-based extinguishers are best used for putting out fires involving solid combustibles like wood, paper and fabric and shouldn’t be utilised anywhere near electrics (unless they contain an additive). Similarly, most people also know that Carbon Dioxide extinguishers can be used to great effect on electrics as well as petrol, oil and solvents.
However, the area where people tend to get confused is with foam and powder extinguishers.
Hopefully, this brief outline of the various attributes and applications of foam and power extinguishers will help to clear up any confusion.
Foam extinguishers are good to have in homes and offices as they are suitable for use on class A solid combustible fires (wood, paper, upholstery) and class B flammable liquid fires (petrol, liquefying plastic, paints). As a rule, foam extinguishers are not to be used on chip pan fires or gas fires.
These extinguishers work by forming a blanket of foam on the burning material, thereby starving a fire of fuel (oxygen). Indeed, the dispersed foam also penetrates deep into burning materials so that it can extinguish deep rooted embers. In addition, the water content of the foam evaporates in the heat and cools the fire down to prevent any risk of re-ignition.
Although dispersed foam presents no immediate risk regarding inhalation, it should be cleaned up as swiftly as possible after dispersal, as the AFFF foams are carcinogenic. Thankfully, the jets on foam extinguishers are able to target relatively small areas therefore most areas are usually quite easy to clean up after dispersal.
Powder extinguishers are the most versatile extinguishers available. Indeed, as well as being suitable for use on class A and B class fires, powder extinguishers can also be used on class C fires (caused by combustion of gasses such as natural gas, propane, hydrogen) and on live electrical equipment. This versatility makes powder extinguishers well-suited to broad range of environments such as workshops, cars, boats and even some homes.
Powder fire extinguishers are more powerful than foam extinguishers; therefore, they are typically smaller than their foam counterparts. Instead of soaking into a burning material, however, powder extinguishers work by forming a crust-like blanket which is able to effectively starve a fire of fuel.
Dispersed powder can be inhaled and therefore care must be taken when it is sprayed. In addition, these types of extinguishers tend to leave a lot of residue behind so there is sometimes a degree of hesitation before powder extinguishers are used within buildings.