●Class A fires are ordinary materials like burning paper, lumber, cardboard, plastics etc.
●Class B fires involve flammable or combustible liquids such as gasoline, kerosene, and common organic solvents used in the laboratory.
●Class C fires involve energized electrical equipment, such as appliances, switches, panel boxes, power tools, hot plates and stirrers. Water can be a dangerous extinguishing medium for class C fires because of the risk of electrical shock unless a specialized water mist extinguisher is used.
●Class D fires involve combustible metals, such as magnesium, titanium, potassium and sodium as well as pyrophoric organometallic reagents such as alkyllithiums, Grignards and diethylzinc. These materials burn at high temperatures and will react violently with water, air, and/or other chemicals. Handle with care!!
●Class K fires are kitchen fires. This class was added to the NFPA portable extinguishers Standard 10 in 1998. Kitchen extinguishers installed before June 30, 1998 are "grandfathered" into the standard.
●Water extinguishers are suitable for class A (paper, wood etc.) fires, but not for class B, C and D fires such as burning liquids, electrical fires or reactive metal fires. In these cases, the flames will be spread or the hazard made greater! Water mist extinguishers are suitable for class A and C; see below. Water extinguishers are effective on pool chemicals provided that they are correctly stored away from electrical hazards and equipment; see the blue box below for more on pool chemicals.
●Dry chemical extinguishers are useful for either class ABC or class BC fires (check the label) and are your best all around choice for common fire situations. They have an advantage over CO2 and "clean agent" extinguishers in that they leave a blanket of non-flammable material on the extinguished material which reduces the likelihood of reignition. They also make a terrible mess - but if the choice is a fire or a mess, take the mess! Note that there are two kinds of dry chemical extinguishers:
●Type BC fire extinguishers contain sodium or potassium bicarbonate.
●Type ABC fire extinguishers contain ammonium phosphate.