What is the correct use of an extinguisher on a class B fire?

The use of foam or dry powder for extinguishing a Class B fire is correct because Class B fires involve flammable liquids such as oils, gasoline, and solvents. Foam extinguishers work by creating a blanket over the burning liquid, cutting off the oxygen supply and preventing re-ignition. This is particularly effective because it not only suppresses the flames but also prevents the fire from spreading.

Dry powder extinguishers are also suitable for Class B fires as they operate by interrupting the chemical reaction that involves the fire. These agents can be effective for a wide range of flammable liquids, making them versatile options in emergency situations.

Using water on a Class B fire is not recommended because it can spread the burning liquid, potentially making the situation worse. Some extinguishing agents, while they can put out fires in other classes, might not be safe or effective for flammable liquids. Therefore, using foam or dry powder is the most appropriate choice for safely and effectively extinguishing a Class B fire.