Remember not all extinguishers are created equal. Some extinguishers have only one hazard rating while others have multiple hazard ratings.
An Extinguisher with a Class A Rating will put out fires of ordinary combustibles, such as wood and paper. The numerical rating assigned to this hazard refers to the approximate square feet of a class A fire that the extinguisher can potentially put out.
An extinguisher with a Class B Rating should be used on fires involving flammable liquids, such as grease, gasoline, oil, etc. The numerical rating for this class of fire extinguisher states the approximate number of square feet of a flammable liquid fire that a non-expert person can expect to extinguish.
An extinguisher with a Class C Rating indicates that the extinguishing agent is non-conductive as the fire involves energized electrical components such as motors, transformers, and appliances.
Class D Extinguishers are designed for use on flammable metals and are often specific for the type of metal in question. There is no designated symbol for Class D Extinguishers. These extinguishers generally have no numerical rating nor are they given a multi-purpose rating for use on other types of fires.
Class K Extinguishers are primarily used for commercial kitchen fires involving cooking oils and greases such as animal fats and vegetable fats.