What phenomenon describes combustion that occurs without external flame exposure?

The phenomenon of combustion that occurs without external flame exposure is best described by the term "Spontaneously Combust." This type of combustion takes place when a material reaches its ignition temperature due to chemical reactions occurring within it, usually caused by factors like heat buildup, oxidation, or the presence of moisture.

In spontaneous combustion, there is no external flame or spark initiating the fire; rather, the heat generated by the ongoing chemical processes causes the material to ignite on its own. Understanding this can be crucial in fields such as safety and materials handling, where the inappropriate storage of certain materials might lead to such uncontrolled combustion events.

The other terms related to combustion are distinct in their definitions. For instance, a flash fire typically involves a sudden and rapid spread of fire initiated by external ignition sources. Pyrolysis refers to the thermal decomposition of materials at elevated temperatures in an inert atmosphere, without the presence of flames or oxygen, which is distinctly different from spontaneous ignition. Self-ignition is a broader term that may describe various phenomena of ignition, but in this context, "spontaneously combust" specifically addresses the scenario of combustion occurring without any external ignition source.