What Is a 40-B Fire Extinguisher?

A 40-B fire extinguisher is specifically designed to fight flammable liquid fires. Water and other extinguishing products that are typically used on ordinary combustibles, such as paper and wood, are ineffective against burning cooking oil, gasoline or similar fires.

Class B Fires

• The "B" in the fire extinguisher designation references flammable liquid fires. Other fire classifications include A (ordinary combustibles), C (energized electrical equipment) and D (combustible metals).

Extinguisher Rating

• The "40" in the designation describes the extinguisher's fire-fighting capacity or rating. A 40-B extinguisher will extinguish twice as much burning liquid as a 20-B device and four times as much as a 10-B.

Fire-fighting Agent

• Class B fire extinguishers can dispense one of several different products, but a dry chemical powder is most common.

Skill Matters

• The actual amount of burning liquid that can be extinguished by any portable Class B fire extinguisher is directly related to the skill of the person employing it.

A 40-B is a Big Fire Extinguisher

• A "40" is the highest rating that can be assigned to a Class B fire extinguisher and usually indicates a filled capacity of at least 75 pounds of dry chemical product.

Too Big to Carry

• Because of their size and weight, 40-B fire extinguishers are usually mounted on a wheeled cart or installed as a fixed extinguishing system. Restaurant kitchens employ 40-B extinguishing systems.