Influence of wood particulate size and moisture content on deflagration hazard

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For many revision cycles NFPA 664 Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities, has used a median particle size to distinguish between particulates that should be considered a potential deflagration hazard from those that can be safely assumed to not pose an explosion hazard. With a numerical median size criterion in the standard, a physical inspection can be employed to identify which portions of the process stream represent a potentially hazardous condition and which do not. The standard defines “deflagrable wood dust” on the basis of mass median particle size and moisture content. This makes the standard much easier and lesscostly to use. Question has been raised over the suitability of both the numerical value of the mass median particle size and the moisture content. The other dust standards rely entirely on dust testing in accordance with ASTM E 1226 with no explicitly identified gross physical parameter quantified. Consequently, one cannot know if a particulate is hazardous without testing it. But the test method relies upon modifying the particulate to accommodate the test apparatus. This can result in the overstatement of the hazard in some cases. It can also result in circumstances where the particulate is impossible to test in the current ASTM method and no conclusion is achievable. In that case compliance with the requirements of the standard becomes impossible. Naturally, this situation erodes the confidence in the standard as a whole.

Research goal: The overall goal of this project is to develop a data set from published literature that may provide basis for substantiating mass median particle size and moisture content criterion for distinguishing wood particulates that are extremely unlikely to pose a deflagration hazard from those that should be submitted for testing. 

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