From smoldering to flaming fire: Different modes of transition

Transition from smoldering to flaming fire in cotton is investigated experimentally for five different sample sizes. Two different modes of transition are identified: early and late transition. Early transition to flaming occurs when smoldering combustion forms a hot glowing core inside a sample. As the smoldering burns through to the outside of the sample, air moves more easily into the core, resulting in a change in smoldering direction from reverse to forward smoldering, causing increased heat production and flaming. Late transition to flaming occurs occasionally after most of a sample is consumed by smoldering, and where randomly appearing glowing spots ignite flammable vapor from smoldering processes.