What is the term for a combustion or decomposition reaction that occurs at a velocity less than the speed of sound?

The term for a combustion or decomposition reaction that occurs at a velocity less than the speed of sound is deflagration. Deflagration is characterized by the generation of pressure and heat that propagates through the reacting material at subsonic speeds. In this type of reaction, the flame travels through the unburned fuel, causing a gradual release of energy which is typically associated with forms of combustion seen in everyday fires.

Understanding deflagration is crucial in explosion hazard assessments, as it often occurs in lower pressure systems and can be managed or mitigated through proper safety measures. This distinguishes it from detonation, where reactions occur at supersonic speeds and involve shock waves, leading to much more severe outcomes. The unique characteristics of deflagration make it a critical concept when examining the safety and design of chemical processes and systems.