Reviewing the OSHA advance notice of proposed rulemaking (ANPR) creates quite a concern. For example in the second sentence of the "Summary" at the top of the page, "For the
purposes of this notice, the term "combustible dust" includes all
combustible particulate solids of any size, shape, or chemical
composition that could present a fire or deflagration hazard when
suspended in air or other oxidizing medium"
So for combustible dust to be hazard it must be suspended in air? What about smoldering layers of dust which also fire and explosion hazards? Before dust can be in suspension it first must be layered on horizontal surfaces. Personnel have been fatally and severely injured from smoldering dust initially not in suspension. Additionally facilities have burned to the ground due to layers of dust.
The problem of OSHA defining combustible dust solely in suspension became readily apparent when trade associations submitted comments in response to the ANPRM requesting their NAICS be removed from "Table 1--Industries Having at Least One Recorded Combustible Dust Incident Reported Since 1980," since combustible dust incidents at facilities they represented were dust layered fires and not in suspension. Was the Dust Incident table (page 43 .pdf) listing severity of consequences (Kst's) instead of NAICS, during a topic of discussion at the 2011 OSHA Combustible Dust Expert Forum a response to the turmoil of defining combustible dust solely in suspension?
There is no mention whatsoever in the OSHA Combustible Dust ANPRM about catastrophic combustible dust related fires as a result of layered dust not in suspension. In stark and awakening contrast, the NFPA Fire Analysis and Research Division prepared a report, "Fires in U.S. Industrial and Manufacturing Facilities" providing insightful information regarding combustible dust related structure fires in manufacturing properties from 2006-2010. The NFPA report noted that shop tools and industrial equipment were involved in 29% of these structure fires.
On a side note, do you know the burning behavior of your dust? Additional information on burning behavior (VDI 2263). Currently OSHA nor CSB recognizes burning behavior in evaluating combustible dust fire and explosion workplace hazards.Unfortunately, we'll have to wait for another catastrophe before burning behavior is reconized like it is amongst our international trading partners.