Class A rating fire extinguishers are often water-based, and are highly effective in extinguishing burning materials found or stored in an office or warehouse for example. Water-based Class A extinguishers may also have additives to make them more effective.
Class B rating fire extinguishers are usually foam fire extinguishers or powder. These extinguishers work by not only extinguishing flames but also sealing in any potentially dangerous vapours.
Class C rating fire extinguishers will be dry powder fire extinguishers that are capable of separating the elements of thee fire triangle.
Class D rating fire extinguishers are highly specialized extinguishers, designed to be used on specific metal fires with such exotic names as M28, L2 and Purple-K. They will have a long lance with a low velocity application on the end.
Class E rating fire extinguishers are specially designed for use on live electrical equipment. While a powder fire extinguisher is non-conductive and safe to use, the most popular fire extinguisher for use on electrical equipment fires is carbon dioxide, which extinguishes flames without causing further damage.
Class F rating fire extinguishers, also known as wet chemical fire extinguishers, are specifically for fires involving cooking oils and fats.