In real conditions, the surface temperature of an equipment enclosure covered with a combustible dust layer can significantly rise due to insulating properties of the dust layer. To assess this effect, the measurements of minimum ignition temperature of dust layer at constant temperature of the heated plate t(l) (min) (standard method) and the same ignition temperature at constant rate of heat generation t(h min) for two coal dusts were made. Dust layers of thickness between 5 and 50 turn were tested. For each dust, t(l) (min) was higher than t(h) (min) for every tested thickness of the layer. The difference was biggest for thin layers and decreased with increase of the layer thickness. The results suggest a deficiency of the standard procedure of measuring minimum ignition temperature of a dust layer. (C) 2003 Elsevier Science Ltd. All rights reserved.