Different Types of Fires

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 is a particularly dangerous extinguishing medium for class C fires because of the risk of electrical shock.

Class D fires involve combustible metals, such as magnesium, titanium, potassium and sodium as well as organ metallic reagents such as alkyl lithiums, Grignards and diethyl zinc. These materials burn at high temperatures and will react violently with water or other chemicals. Handle with care!!

Common Extinguisher Types and Some of Their Uses

Water extinguishers (not pictured and not found in laboratories) are suitable for class A (paper etc.) fires, but not for class B, C and D such as burning liquids, electrical fires or reactive metal fires. In these cases, the flames will be spread or the hazard made greater!
Dry chemical extinguishers are useful for class ABC fires and are your best all around choice. They have an advantage over CO2 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.
CO2 (carbon dioxide) extinguishers are for class B and C fires. They don't work very well on class A fires because the material usually reignites. CO2 extinguishers have an advantage over dry chemical in that they leave behind no harmful residue -- a good choice for an electrical fire on a computer or other delicate instrument. Note that CO2 is a bad choice for a flammable metal fires such as Grignard reagents, alkyllithiums and sodium metal because CO2 reacts with these materials. CO2 extinguishers are not approved for class D fires!

Metal/Sand Extinguishers are for flammable metals (class D fires) and work by simply smothering the fire. You should have an approved class D unit if you are working with flammable metals.
Check out the potential fire hazards in your home or office. Are your existing fire extinguishers suitable for the fires you may encounter? Contact your local Fire Marshal's office to verify that you have the appropriate extinguisher for your home or office and to see if they offer any training on how to properly use them. The above information is just for general

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