Smoldering combustion occurs in which fuels?

• A. Fast-growing grasses
• B. Wood with high moisture only
• C. Duff, peat, or soil layers
• D. Fresh green leaves

Answer: (C)

Smoldering combustion is the slow, flameless burning that happens in solid fuels where heat and oxygen move through the fuel rather than from a flame on the surface. Duff, peat, and soil layers fit this scenario because they are thick, porous organic materials with plenty of internal spaces for heat to build and oxygen to diffuse. This allows oxidation to proceed at a low temperature, letting the fire creep and persist within the organic layer or underground long after surface flames have died. Fresh green leaves and grasses tend to burn with flames when they dry, since their fuels ignite quickly and support a flame front. Wood with high moisture is hard to ignite and usually doesn’t sustain the same steady, surface-free burning seen in smoldering fuels, so it isn’t the classic example.