Both OSHA PRCS standards define and quantify a Hazardous Atmosphere in terms of combustible dust using the distance one can see through the dust cloud…
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Hazardous atmosphere means an atmosphere that may expose employees to the risk of death, incapacitation, impairment of ability to self-rescue (that is, escape unaided from a permit space), injury, or acute illness from one or more of the following causes: … (2) Airborne combustible dust at a concentration that meets or exceeds its LFL; Note: This concentration may be approximated as a condition in which the dust obscures vision at a distance of 5 feet (1.52 m) or less. |
The “note” seems to exempt us from measuring the atmosphere, which is good because I don’t think most facilities can measure dust concentrations. But having so much suspended dust that I can not see 5′ is a lot of dust!
Does your program accept this quantity of combustible dust to be suspended in the atmosphere of space?
We always used “any visibly suspended dust” as our measure, as we had several different combustible dusts with widely varying LELs.
For example:
