concept

Flame blow-off

Extinction by airflow rather than by lack of fuel or oxygen. A flame needs a certain dwell time to breed the radicals that keep it going; if the flow sweeps the reacting gas past faster than that, heat and radicals are stripped out of the reaction zone quicker than they are made. The condition is written compactly as the Damköhler number, the ratio of flow residence time to chemical reaction time: below 1, the flame goes out. For thin fuels carrying unshielded diffusion flames the threshold is startlingly low - only about 4-8.5 m/s, a moderate breeze.