Practical Issues with Marginally Explosible Dusts - Evaluating the Real Hazard

A combustible dust can be non-explosible, marginally explosible or severely explosible. With the exception of a few standards with a quantitative perspective (such as NFPA 68), most safety standards and regulations do not differentiate marginally explosible dusts from severely explosible dusts. As a result, a marginally explosible dust triggers the same legal and technical burden on the users as a severely explosible dust does. The issue is further complicated owing to the fact that the standard explosibility test method is inherently inaccurate when it comes to marginally explosible dusts. This paper demonstrates that OSHA tests can classify non-explosible dusts erroneously as explosible. This paper reviews the state of the art on this topic, and provides a comparison of internationally recognized explosibility/combustibility evaluation test methods with those currently used by OSHA. It also highlights the upcoming substantive changes, being implemented to resolve some of the common issues, in the codes and standards pertaining to life safety, property conservation and electrical area classification.