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Explosion Venting/Suppression Q&A

  •   We work with several difference powders in the pharmaceutical manufacturing industry (weighing, blending, tableting, etc.). Many of the explosivity numbers (Kst, dP/dT, etc.) help determine how severe an explosion would be, should it occur. However, when evaluating chemical powders to see if we can handle them in our facility, if we test and know the MEC of each chemical (to simplify the testing and maximize cost effectiveness), and can keep the dust levels well below the MEC, do we have to know any of the other explosivity testing values (Kst, Pmax, dP/dT, MIE, etc.) when trying to ensure an explosion won’t occur?

    Answered December 7th, 2015 by Expert: Dr. Gerd Mayer

    In theory, this seems to be the true. And, yes, if you have total control of all aspects of the process and can control the dust concentration through every aspect of the process, then you should not need to do more–in theory. NFPA Standard 69, 2014 edition, even says so. See Chapter 8, Deflagration Prevention by Combustible Concentration Reduction.

    Here’s the problem:  the dust concentration changes throughout the process. Can you really assure yourselves you can control the concentration such that you are always maintaining a level that is well below the MEC? Think about what happens at your dust collectors. Do you really have control of the amount of dust that accumulates on the filters/bags? Will there be a “mishap” there? I am always concerned about the human factor: will a broken filter bag be detected and replaced immediately? Will filter bags be replaced immediately at the precise time they need to be? All this and much more during the process can affect the MEC and the ability to control your dust concentration.

    If your authority having jurisdiction is willing to accept this approach based on documentation that shows you can and will control the dust concentration to maintain a level well below the MEC, then you are good to go.

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