Presence of carbon dust

[thinker]

The customer's request for quotation for assembly line specified the presence of carbon dust with concentration 0.5 milligrams per cubic meter. Should this be treated as hazardous location Class II per NEC? Is there any reference related the numerical value of dust concentration? Please advise.

 

[rbalex]

This is a very interesting question. NFPA 499 is the Standard for classifying Group II materials. It defines Combustible Dusts as:
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Any finely divided solid material 420 microns or less in diameter (i.e., material passing through a U.S. No. 40 Standard Sieve) that presents a fire or explosion hazard when dispersed. Combustible dusts are subdivided as follows:
…
Group F. Atmospheres containing combustible carbonaceous dusts that have more than 8 percent total entrapped volatiles (see ASTM D 3175 for coal and coke dusts) or that have been sensitized by other materials so that they present an explosion hazard. Coal, carbon black, charcoal, and coke dusts are examples of carbonaceous dusts.
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Based on those definitions, I’d have a hard time finding “…0.5 milligrams per cubic meter,” the likely to necessitate classifying the process.

 

[tictok]

In trying to determine the classification of our product, we actually performed the following steps:
1) Found we did not have any product greater than
8% volatiles,
2) Then we performed a 24 and 48 hour dust accumulation
test that showed we did not have a hazardous
accumulation of dust.
3) Examined our past experience (100+ years) to also
substantiate the non hazardous trait of our dust.