Classes of fires
Not all fires are the same. If you use the wrong type of fire extinguisher on the wrong class of fire, you can, in fact, make matters worse. It is therefore very important to understand the 4 different classes of fires

class A fire    

 

 

 

 

  
One of four categories of fires. Class A fires involve solid combustibles (such as wood or paper), which are best extinguished by water or dry chemicals. A portable fire extinguisher using water or dry chemicals is called a "class A extinguisher."
 
class B fire
One of four categories of fires. Class B fires involve flammable liquids, which are best extinguished by foam, carbon dioxide or dry chemicals. Portable extinguishers using these agents are called "class B extinguishers."
 
class C fire
One of four categories of fires. Class C fires involve live electrical equipment which must be extinguished by a nonconductive extinguishing agent such as carbon dioxide or dry chemicals. An extinguisher using either of these agents is called a "class C extinguisher."
 
Class D fire
Class D fire - Combustible Metals: potassium, sodium, lithium, aluminum, magnesium and metal swarf. Fires of this class may occur in laboratories or industries that use these materials. Metal swarf fires may occur in machine shops where metal turning or milling is carried out. These fires burn at high temperatures and give off sufficient oxygen to support combustion. They may also react violently with water or other chemicals