Class A
Fires involve ordinary combustibles, like wood, paper, cloth, trash, and plastics. They do not contain metals, combustible liquids, or electricity. (Class A fires generally leave Ashes.)
Class A fires can be extinguished with water. A Class A extinguisher is typically either a pressurized can of water that can be sprayed on a fire or a container of water with a pump mechanism. Class A extinguishers are for use only on Class A fires. A Class A fire extinguisher is marked with a green triangle containing the letter A. An alternative method of extinguishing a Class A fire is to smother it with a blanket, a gloved hand, or other material.
Class B is liquid fuel and Class C is gaseous fuel , as per ISO . Electrical is not considered as a class of fire but as a source of ignition.
As per NFPA (only American) class B is considered as liq/gas and class C as electrical.