spontaneous combustion
From Longman Dictionary of Contemporary Englishspontaneous combustionsponˌtaneous comˈbustion noun [uncountable] BURNburning caused by chemical changes inside something rather than by heat from outsideExamples from the Corpusspontaneous combustion• Indeed, the playing is quite riveting, creating a feeling of spontaneous combustion.• Imagine the response of early humans to fire caused by volcanoes or spontaneous combustion.