A Physico-Chemical Basis for "Explosibility INDEX" and APPLICATION to Electrical CLASSIFICATION and Explosion HAZARD Evaluation

In 1980, the National Materials Advisory Board of the National Research Council used the Ignition Sensitivity and Explosion Severity to aid in determining appropriate electrical classifications for combustible dusts [Reference 4]. The statement was made that "any dust having an ignition sensitivity equal to or greater than 0.2 or an explosion severity equal to or greater than 0.5 [both by comparison to Pittsburgh coal dust] should require electrical equipment suitable for Class II hazardous locations." This statement has been interpreted by the National Fire Protection Association to indicate that dusts with an ignition sensitivity that is less than 0.2 and an explosion severity that is less than 0.5 [both by comparison to Pittsburgh coal dust] "are generally not considered to be significant explosion hazards" and "Area classification is not considered necessary for dusts that meet both criteria" [Reference 5].

The use of Ignition Sensitivity and Explosion Severity by the U. S. Bureau of Mines can be extended to present-day ranking of a wide range of combustible materials. The products of explosibility properties appear to have a sound physico-chemical basis and can be used to prioritize efforts in electrical classification and in Process Hazards Analyses.