Information is presented for the relationship between fire and explosion risk of dusts and the equivalent particle diameter. Theoretical premises as to the variation of the lower concentration limit of the spread (LCLS) of the flame as the size of the disperse phase of the aerosol diminishes to "nano" dimensions, and also experimental data permitting comparison of LCLS values for aerosols of micro-and nano-particle organic substances are examined. A brief analysis and conclusion concerning the data obtained is presented.