Classification of Fires

Classification of Fires

Should the nature and size of the fire make it controllable, use the appropriate available extinguisher and proceed with the methods described below.  Should the fire be judged “uncontrollable”, follow the “Evacuation Procedures for Uncontrollable Fires”.

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)
If sodium, potassium, magnesium, or any other flammable metal powders are to be used in a laboratory, call EH&S for guidance on the appropriate dry powder-extinguishing agent. A specific "Class D" (dry powder) extinguishing agent such as graphite, limestone, sand or sodium carbonate must be made available for fire emergency before work is started.

DO NOT USE pressurized water, carbon dioxide, dry chemical or halon extinguishers on metal or organometallic fires.  The use of these extinguishers may introduce substances that are very reactive with the burning metal that may either make the fire grow or trigger an explosion.