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Keywords:

  • combustible;
  • explosible;
  • dust;
  • powder;
  • layer;
  • accumulation;
  • thickness;
  • hazard;
  • threshold;
  • prevention;
  • protection;
  • consequence;
  • explosibility;
  • screening;
  • deflagration;
  • flash fire;
  • explosion;
  • NFPA;
  • OSHA;
  • NEP;
  • ASTM

Abstract

A combustible dust can be nonexplosible, 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 article demonstrates that OSHA tests can classify nonexplosible dusts erroneously as explosible.

This article 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 changes originally proposed for the NFPA-654, 2011 edition, which will be further considered as the document has been returned to committee for review, as well as proposals for the NFPA-499, 2012 edition. These new approaches are intended to resolve some of the common issues in the codes and standards pertaining to life safety, property conservation, and electrical area classification. © 2011 American Institute of Chemical Engineers Process Saf Prog, 2011.