The smouldering of powdered cocoa, grass and cork has been investigated; these powders are industrial hazards because of their liability to produce dust explosions. The dusts were formed into small trains; smouldering was then initiated and its linear rate of propagation measured. The minimum depths of train necessary to sustain smouldering were also determined, in some cases they were very small (2-3 mm). Experiments with trains of cork dust supported upon metal or asbestos showed that the the burning time of the dust was not measurably affected by the thermal conductivity of the supporting base. Smouldering in all the dusts was initiated easily by a cigarette end.