There are a number of different fire extinguishing media types available. The media used depends on the class of fire to be extinguished. Portable extinguishers are designed to be carried and operated by hand and have a mass of less than 20Kg.
The most common is water as it is an effective cooling agent and is especially effective on Class A fires (solids). Remember it should not be used on fires where the electric is energised or on Class B fires (flammable liquids), Class D (metals) or on Class F (cooking oils and fats).
Water with Additives.
Some water extinguishers now come with an additives to increase itís effectiveness and a 3 Litre extinguisher of this type operated correctly is as effective as a 9 Litre water.
Most effective on Class B fires (flammable liquids) and they are also effective on class A fires (solids). Because of their water content they must not be used on Class F fires (cooking oils & Fats) nor should they be used on Class D fires (metals).
Powder extinguishers consist of fine particles of chemicals of various kinds and are found with different purposes on their labels. BC powder extinguishers consist of Sodium or Potassium Bicarbonate and are effective on Class B (flammable liquids) and Class C (gasses) they do not conduct electricity. High performance blends are used in the petrochemical and aviation industries, trade such as Monnex and Purple K. ABC powder extinguishers contain Mono-Ammonium Phosphate compounds and smothers Class A fires (solids) and chemically inhibits combustion in Class B (flammable liquids) and Class C (gasses) fires, it also does not conduct electricity. D powder extinguishers are for Class D (metal) fires and consist of Sodium Chloride, Graphite or Copper compounds that are designed to melt and form a crust around the metal smothering the fire and allowing the metal to cool.
Carbon Dioxide. CO2.
Carbon Dioxide extinguishers are electrically non conductive and as such ideal for fires involving energised electrical equipment. It can be effective on small Class B fires (flammable liquids). It is ineffective on Class A (solids), Class D (metals) or Class F (cooking oils & Fats).
Care must be taken when using CO2 as the discharge horn gets very cold in use and can cause cold burns (just as serious as hot burns).
Wet chemical extinguishers contain an alkaline solution of Potassium Acetate that reacts with the burning oil or fat of a Class F fire (cooking oils and fats). This reaction turns the surface into a soapy crust sealing it from the air, (this is called saponifying). Due to itís water content it is effective on Class A fires (solids), but, it is a conductor of electricity.
These extinguishers contain complex chemical compounds that when released interfere with the chemical reaction of combustion. They mainly consisted of Halons which the use of is now banned (Montreal Protocol) and should only be found in certain exempted areas such as aviation. Although alternative environmentally friendly agents are now available they are rarely found in portable extinguishers.