Should the nature and size of the fire make it controllable, use the appropriate available extinguisher and proceed with the methods described below.
CLASS A. (Wood, paper, textiles, rubber). The ABC extinguisher can extinguish this type of fire.
CLASS B. (Flammable or combustible liquids, greases, petroleum products, solvents)
Carbon dioxide or dry chemical ABC extinguishers should be used. Carbon dioxide extinguishers do not leave any residue, whereas dry chemical devices do. Pressurized water units should not be used since the immiscibility of solvents and water may result in spreading of the fire.
CLASS C. (Live electrical equipment involved in a fire). If possible, turn off the electrical power to the devices, and then use either the dry chemical extinguisher or a carbon dioxide or halon extinguisher, if available.
CLASS D. (Sodium, potassium, magnesium, titanium, zirconium and other metals)
A specific “Class D” (dry powder) extinguishing agent such as graphite, limestone, sand or sodium carbonate can be used to put out this type of fire. Smothering the fire with sand or salt may also be used.
CLASS K. (Cooking Oil, Fats). New classification from the National Fire Protection Association. To put out a fire of this class use a wet chemical extinguisher.
Source: Columbia University http://ehs.columbia.edu/Policy4.2.html