Dust particles have a minimum or lower explosive limit to almost no upper limit. Here are examples of minimum explosive limits (oz/ft3): Polystyrene (0.02) Cornstarch (0.04), Coal (0.055), Iron (0.12).
It is important to note an explosimeter gives a reading as a percentage. The reading is based on the percentage of the LEL and not the full concentration of the vapour or gas in the mixture. For example a 50% explosimeter reading of a gasoline/air mixture really translates into 0.7% gasoline (50% of 1.4%, the LEL). It is common practice to consider a 10% explosimeter reading or 10% of the LEL, as a safe working area. When taking explosimeter readings, consider the possibility that the vapour or gas may have accumulated in recessed areas (top or bottom of tank depending on the density of the gas or vapour).