Each fire extinguisher has its own symbolic notation, that is a special geometric symbol to make it easier for you to identify the extinguisher type. They also have some additional information necessary in case of this or that class of fire fighting.
Class A fire extinguishers, for example, have the green triangle on them and also the special numerical rating, showing the amount of water this extinguisher holds and the amount of fire it is able to extinguish.
Class B fire extinguishers are marked with the red square and have the numerical rating indicating the approximate area of fire (in square feet) it is able to extinguish.
Class C fire extinguishers are marked with the blue circle, but they don’t have any numerical rating. As a rule they contain the non-conductive extinguishing agent, because they are often used for electrical fire fighting.
Class D fire extinguishers have the yellow decagon on them and are mostly regarded as the part of chemical laboratory firefighting equipment. They also don’t have any numerical rating on them. There are also class K fire extinguishers, marked with the black hexagon. They are intended for the fighting the fire, caused by any cooking oils, fats or trans-fats combustion and are highly recommended for restaurant or cafeteria kitchens.
There is also another fire extinguishers classification based on their contents nature. According to this classification there are water, foam, dry-powder and CO2 fire extinguishers.
Water or APW (Air pressurized water) fire extinguishers are as a rule recommended for class A fire fighting and are effective in case of wood, paper or plastic ignition. Their operation principle is based on the reducing the temperature of the burning materials below their ignition temperature. The APW units, available in the USA, as a rule, are made of stainless steel and contain 2.5 gallons (9 liters) of water. Their main advantage is their price and their harmlessness. As for the disadvantages… Well, they cannot be used in case of class B fires or electrical fires, and mostly are recommended for the class A fire fighting only. There are also Water Mist fire extinguishers, very popular in hospitals. These harmless and non-contaminant fire extinguishers contain 1.75 or 2.5 gallons of water and can be used both for class A and class C fires fighting. Foam fire extinguishers are as a rule used in case of class B fires. The foam, contained in them, reduces the oxygen around the fire. They are able to progressively put out the fire without any flashback. Depending on their contents there are AFFF (aqueous film forming foam), AR-AFFF (Alcohol-resistant aqueous film forming foams), FFFP (film forming fluoroprotein), CAFS (compressed air foam system), Arctic Fire and FireAde fire extinguishers. AFFF units are portable foam extinguishers, used for class A and class B fires fighting as well as for vapor suppression. AR-AFFF units are used in case when fuel, having caused the fire, contains alcohol, and are able to create the alcohol-resistant foam blanket. FFFP fire extinguishers are very at hand in case of alcohol-based liquids ignition, as they are able to create the heat resistant foam blanket and thus effectively put out the class C fire. CAFS, containing the special foam solution at high air pressure, are mostly used for water supply extension or (in case of A class fire or, if with the very dry foam contents, in case of B class fire) for vapor suppression. Arctic Fire extinguishers are very interesting and effective firefighting equipment solution, as they contain the special agent, able to cool and emulsify the heated and ignited materials faster than any water or foam fire extinguisher does. They are highly recommended for use in case of class A, B or D fires. FireAde extinguishers have something in common with Arctic Fire units, as they operate on the same principle, turning the ignited liquids into non-inflammable ones thanks to their special temperature reducing agent. But unlike Arctic Fire units, these ones are recommended for use in case of class A or class B fire only.
Dry powder fire extinguishers as a rule contain some powder based agent, able to break the chemical chain reaction, sustaining the fire. There are monoammonium phosphate (“tri-class” or “multipurpose”) units, belonging to this group, that are recommended for use in case of class A, B, and C fires, sodium bicarbonate fire extinguishers, that prevent the oxygen reaching to the fire, discharging the carbon dioxide and are used on class B and C fires, or potassium bicarbonate (also famous as aka Purple-K) extinguishers, popular in oil and gas industry for their powerful effect in case of class B or C fires. The dry powder fire extinguishers also include Potassium bicarbonate & Urea Complex units, effective on Class B and C fires thanks to their agents ability for decrepitation and inhibition of fire sustaining free-radicals production on large surface areas, then Potassium Chloride, or Super-K units, containing protein-foam compatible dry chemical, very effective in case of class B or C fires, or Foam-Compatible units, containing sodium bicarbonate based dry chemical, effective on class B or C fires and using silicone as a waterproofing agent, what makes them compatible with most of synthetic foam fire extinguishers. One of the most special dry powder fire extinguishers kinds is the MET-L-KYL / PYROKYL units, contains silica gel particles, preventing the unburned fuel contact with air. It makes this type of fire extinguishers irreplaceable in case of pyrophoric liquid fires, as well as in case of any other class B fires. The dry-powder fire extinguishers are very effective and popular in many industries as the reliable fire equipment, but the disadvantage of some of them is that some of the agents they contain turn to be rather corrosive and thus must be quickly removed from the surface.
Carbon dioxide(CO2) and other clean agents containing fire extinguishers operate almost on the same principle that the dry-powder extinguishers do. They inhibit the chemical chain reaction, sustaining the fire, but have one great advantage here – they don’t leave any residue after the discharge, what makes them invaluable as the part of firefighting equipment for offices. The fire extinguishers of this type as a rule contain halon (a gaseous agent, inhibiting the chemical reaction of fire and effective in case of class B or C fires) or CO2, able to reduce the oxygen around the fire area. They can also contain the mixtures of inert gases, like Inergen and Argonite. There are Novec 1230 fluid units, containing fluoronated ketone. These ones are able to cool the surfaces and objects on fire very fast and effectively. Sorry to say, portable Novec 1230 fluid extinguishers are not available in the US, but their special clean agent is used in fixed firefighting systems, already available in America.