Describe two fire behavior differences between Class A (ordinary combustibles) and Class B (flammable liquids) fuels.

• A. Class A typically burns with growth from solid fuels and leaves embers; Class B burns as vapors from liquids and can spread quickly with flammable vapor plumes.
• B. Class A fuels burn in water and Class B fuels burn in air.
• C. Class A produces no smoke and Class B produces heavy smoke.
• D. Class A burns indoors only and Class B burns outdoors only.

Answer: (A)

The key idea is how the fuel actually feeds the flame and how the fire spreads. Class A fuels are solids, so the fire grows by burning the solid material itself. As heat is applied, the surface chars, forms embers, and continues to burn from the solid mass, often leaving glowing embers and ash as the fire persists.

Class B fuels are liquids, so the fire is fed by evaporated vapors rather than the liquid bulk. The liquid vaporizes, the vapors mix with air, and ignition occurs in the vapor phase. Those flammable vapor plumes can travel and spread quickly beyond the original liquid source, leading to rapid fire growth.

So, two differences are: solids burn by the fuel itself with embers forming, while liquids burn via vapors that can disperse and fan flames quickly.