deflagration

nopea palaminen The act of deflagrating; an intense fire; a conflagration or explosion. Specifically, combustion that spreads subsonically via thermal conduction.
1849 Heinrich Rose - A Practical Treatise of Chemical Analysis

If, for example, the mixture of oxygen and hydrogen was twenty volumes, and three volumes of oxygen remained after the deflagration, the mixture consisted of six volumes of hydrogen and six volumes of oxygen.

Black powder . . . It produces a relatively fast burn or deflagration rather than a detonation and is classified as "low explosive".