The conventional theory of combustion describes systems where all of the parameters are spatially homogeneous. On the other hand, combustion in disordered explosives has long been known to occur after local regions of the material, called hot spots, are ignited. In this article we show that a system of randomly distributed hot spots exhibits a dynamic phase transition, which, depending on parameters of the system, can be either first or second order. These two regimes are separated by a tricritical point. We also show that on the qualitative level the phase diagram of the system is universal. It is valid in two and three dimensions, in the cases when the hot spots interact either by heat or sound waves, and in a broad range of microscopic disorder models.