While the term thermal explosion sounds very dramatic, it really just refers to a thermal event where the heat release (or absorption) occurs over a time period that is very small relative to the time scale of interest, and in a volume that is negligibly small compared to the surroundings in which the temperature distribution is to be calculated. So, for example, the heat released by the combustion of blasting powder in a small hole (time scale of milli-seconds) could be analyzed as a thermal explosion if the time scale of interest was on the order of seconds. Also the decay heat generated by a pocket of radioactive rock (say, over 100 years) could be analyzed as a thermal explosion if the period of interest were, say, 10,000 years.
