闪燃现象一般发生在一个起了火的密闭空间，因为现场积聚大量可燃物质，当密封燃烧下，令温度持续上升至逾摄氏500度时，火场会在一至两秒间因为场内所有可燃物体被高温点燃自动燃烧而全场起火，变成一片火海，极为致命。

闪燃的概念是由英国科学家P. H. Thomas于1860年代提出，其他学者仍然持续地对闪燃理论发表相关的研究。

A flashover is the near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area. When certain organic materials are heated, they undergo thermal decomposition and release flammable gases. Flashover occurs when the majority of the exposed surfaces in a space are heated to their autoignition temperature and emit flammable gases (see also flash point). Flashover normally occurs at 500 °C (932 °F) or 590 °C (1,100 °F) for ordinary combustibles, and an incident heat flux at floor level of 20 kilowatts per square metre (2.5 hp/sq ft).