Eight extinguishing powders were tested in five types of diffusion flames. The effect of flame temperature on the inhibition efficiency was investigated by varying the oxygen index of the flame- supporting atmosphere. In addition, a spectrographic investigation of powder-flame dissociation products was carried out on the methane- air-abc (nh4h2po4) flame. Dissociation products for this flame included po, ph, nh, and na. It was concluded that the main factor to be considered in the efficiency of the powder is the flame temperature. Purple k (khco3) was typically inefficient in low- temperature flames and very efficient in high-temperature flames. On the other hand, abc (nh4h2po4) was found to lose its efficiency at high temperatures but to be quite efficient in the low- temperature flames. The effect of temperature is offered as an explanation of the poor efficiency of khco3 against coal dust explosions in contrast to the high efficiency of the phosphate salts against coal dust explosions.