Evidence is assembled to show that a common mechanism in coal pyrolysis is the explosive ejection of gas, fluid and/or solid as the result of build up of internal pressure and its sudden release by mechanical failure. Individual particles of swelling coal in the pulverized fuel range become fluid droplets when heated to their range of fluidity and they swell and burst before or after the hardening of an outer skin which enhances the bursting pressure, leaving behind hollow cenospheres of char. Larger particles of swelling coals develop a strong solidified outer skin that bursts more violently to give trails of fluid coal and thick walled cenospheres with a discontinuous kernal. Non caking particles may also develop bursts of pressure release from sealing of release channels by softened coal. The explosive ejection hypothesis can explain several features of coal pyrolysis kinetics which are otherwise difficult to explain. They include the unexpectedly good fit of kinetic equations, their frequent division into a dual mechanism, the low 'activation energy', the effects of pressure and of particle size, the comparative absence of evidence for tar distillation and the relative unimportance of rank. Beds of fine coal when pyrolysed slowly also display explosive ejection, as is shown by thermobalance experiments and by the volcanic cones of the crucible swelling test.