The Hazardous Materials Identification System, or HMIS, has adopted the OSHA criteria for determining flammability and physical hazards.
Care should be used in the application of flammability and physical hazard ratings to combustible dusts. The explosion hazard potential of a combustible dust is similar to the explosion hazard of flammable liquid vapors or combustible gases. The major difference is that a combustible dust must be put into suspension by some outside mechanism before an explosion can occur, whereas the flammable liquid vapors and combustible gases have their own capability of diffusing with air to provide possible explosive mixtures.
Keep in mind that the HMIS is intended to provide ratings for normal workplace use, rather than worst-case conditions. Therefore, the HMIS® user should not misapply unnecessarily high flammability ratings to combustible dusts so as to reflect the worst-case scenario. Doing so will confuse the end user and mask the significantly greater hazards of the true fire and explosion potential of materials such as metal powders. HMIS is intended to reflect the relative hazard of materials.