Explosibility testing of sodium azide (NaN3), and two new iron oxide-based gas generants, designated as GG1 and GG2, was conducted according to standard procedures. All the dusts were explosible in the range 0-2.0 kg m(-3); however, rates of pressure rise were sufficiently low to place them in dust class St. 1. Both the explosion pressures and rates of pressure rise increased without showing a marked maxima for dust loadings up to 2.0 kg m(-3). This behaviour is quite different from that observed with most combustible dusts which show maxima in the range 0.50-1.0 kg m(-3). The explosibility characteristics depended strongly upon ignition energy. The minimum explosible concentration (MEG) increased, and the rate of pressure rise decreased, on reducing the ignition energy from 5 kJ to 2.5 kJ. Both iron oxide-based gas generant formulations were less explosible as dusts than sodium azide alone. Based on a number of different variables, the following ranking for dust explosibility hazards is proposed: GG2 < GG1 < sodium azide Of the two formulations, the one which had the higher amount of iron oxide was the least hazardous.