Class-A fires are used all around buildings and everywhere in the world in controlled circumstances, such as a campfire, lighter, match, or candle. This makes an example easy to come by. For example, a campfire has a fire triangle – the heat is provided by another fire (such as a match or lighter), the fuel is the wood, and the oxygen is naturally available in the open-air environment of a forest. This fire is not dangerous, because the fire is contained to the wood alone and is usually isolated from the ground by rocks. However, when a class-A fire burns in an environment where fuel and oxygen are in accessible positions, the fire can quickly grow out of control; this is the case where firefighting and fire control techniques are required.

Class-A fires are fairly simple to fight and contain – by simply removing the heat or oxygen (or in some cases fuel), the fire triangle collapses and the fire dies out. The most common way to do this is by removing heat and oxygen by spraying the burning material with water. Other means of control or containment would be to “smother” the fire with carbon dioxide or nitrogen from a fire extinguisher, cutting off its oxygen and causing the fire to die.

Class-A fires are the most commonly encountered fires, and as such most fire departments have equipment to handle them specifically. While this is acceptable for most ordinary conditions, most firefighters find themselves having to call for special equipment such as foam in the case of other fires

In Europe and Australasia, a different classification system is used.

Class A: Fires that involve flammable solids such as wood, cloth, rubber, paper, and some types of plastics.

All classes of fires same answer as the others.

http://www.nyc.gov/html/fdny/html/safety/extinguisher/classes.shtml

plus 2 new ones.

once again hummmmmm!