Eleven experiments were conducted at the University of Canterbury using a 1.0 metre by 1.0 metre by 1.5 metre compartment and wooden crib fires. The main objective of these experiments was to produce smoke explosions, and to develop a mechanism that explains their occurrence. Spontaneous smoke explosions were produced in four experiments. The largest of these explosions produced pressures in excess of 2.5 kPa. All the smoke explosions produced were the result of smouldering fires, all of which started out as under-ventilated fires. Of the six smoke explosions produced, investigation of the results indicates that a single process was responsible for the occurrence of each explosion. A mechanism was developed for the smoke explosions. Oxygen concentration is suspected as the trigger that determines when the explosion occurs.