For Class B fires, which extinguishers are generally suitable?

• A. Water-based extinguishers
• B. Wet chemical extinguishers
• C. Class D extinguishers
• D. Foam extinguishers

Answer: (D)

Class B fires involve flammable liquids, so the extinguishing method must both cool the liquid and keep fuel away from the air. Foam extinguishers do this well by forming a stable foam blanket that sits on the surface of the liquid. This blanket cools the fuel and creates a barrier between the liquid and the air, which reduces vapour release and helps prevent reignition.

Water-based extinguishers aren’t ideal for Class B because water can spread the flammable liquid and fan the fire, making it worse. Wet chemical extinguishers are designed for cooking oil fires and work differently (they form a soapy layer but aren’t suitable for general flammable liquids). Class D extinguishers are for metal fires and won’t be effective on liquids.

So, foam extinguishers are generally suitable for Class B fires because of their ability to blanket and cool flammable liquids, cutting off the fuel–air interaction that fuels the flame.