Fire Extinguishers - Common Types

• Air-pressurized water extinguishers (APW).
• Carbon dioxide fire extinguishers.
• Multi-purpose dry chemical extinguishers.

Air-Pressurized

Air-pressurized water extinguishers (APW) are commonly used on type A fires involving ordinary combustibles. They are recognized easily by their large silver container. 

APW extinguishers are filled two-thirds of the way with ordinary water and pressurized with air.

They extinguish the fire by cooling the surface of the fuel to remove the "heat" from the fire triangle (heat, oxygen, and fuel).

APW fire extinguishers should never be used on fires involving energized equipment. Water is a good conductor and may cause electrical shock and even electrocution.

Water is also ineffective at extinguishing flammable liquid fires. The water actually can spread the fire rather than extinguishing it.

Carbon Dioxide (CO2)

This type of fire extinguisher is filled with nonflammable carbon dioxide (CO2) gas. 

These extinguishers put out the fire by displacing oxygen, or taking the oxygen element out of the fire triangle.

They are not recommended for Class A fires. They will extinguish the flame, but the combustible material may smolder and reignite.

Multi-Purpose/Dry Chemical

Multi-purpose or dry chemical fire extinguishers extinguish a fire by coating the fuel with a thin layer of fire-retardant powder, separating the fuel from the oxygen.

Dry chemical fire extinguishers may be marked multi-purpose, meaning that they can be used for class A, B, or C fires.

They are usually red in color, and weigh between five and 20 pounds.

Source: Joe Mlynek is president of Progressive Safety Services LLC, Gates Mills, OH; joe.mlynek@progressivesafety.us; and content creation expert for Safety Made Simple, Inc., Olathe, KS; joe@safetymadesimple.com