An accumulated combustible dust layer on some hot process equipment, such as grinders, dryers, hot bearings, etc., can be ignited and lead to fires if the hot surface temperature is sufficiently high. Experimental tests are used to determine the minimum hot surface temperature for dust ignition, the ignition temperature of dust itself, and the ignition times in this study. Egyptian rice husk dust is sieved into different sizes (particle diameters) to be used in this investigation. The effects of the dust particle size and the sample size (depth of the dust layer) on ignition parameters are tested. The boundary between the ignition and non-ignition conditions is investigated precisely through a large number of tests. The results show that the minimum hot plate temperature for ignition of dusts decreases as the dust layer depth increases.