Combustion happens in two regimes. Flaming combustion burns pyrolysis gases in the air above the fuel, is fast, reaches around 1200 degrees Celsius or more, emits visible flame and strong infrared, and produces fine sooty particles. Smouldering combustion oxidises the solid char directly at its surface without a flame, runs at perhaps 500 to 700 degrees Celsius, spreads a thousand times more slowly, in millimetres per minute rather than metres, and produces large quantities of pale, cooler smoke rich in carbon monoxide. Smouldering can persist for hours or days in a mattress, a duff layer or a peat bed, and can later transition to flaming when it reaches loose fuel and enough air. The rule to carry is that low temperature and low light output do not mean a small hazard: a smouldering fire is the classic overnight killer indoors and the classic holdover fire outdoors. The confusion it resolves is treating flame as the definition of fire. After this Concept you can classify a fire as flaming or smouldering and state how fast and how visible it will be.
Smoldering combustion is a form of combustion, within fire science, defined as slow, low-temperature oxidation of a material under limited oxygen availability that releases heat and combustion by-pro…