The critical temperature as well as the critical flux for ignition of a dust layer of cornflour and a mixture of wheatflour and cornflour (80% wheatflour+20% cornflour) on a hot plate have been determined. The moulded sample was cylindrical in shape and of different heights and diameters. The particle size of dusts ranged between 63 mu m to 150 mu m. The temperature-time histories for self-heating without ignition and with ignition are offered, showing the critical boundaries between them. Also the times to ignition for each dust, showing the effect of sample size on their values, are determined-Certain experimental correlations which relate to times to ignition, as well as the critical temperature for ignition and thermal and geometrical dimensions of sample are presented.