How will OSHA compliance officers interpret a “condition in which the dust obscures vision” with reference to the definition of a hazardous atmosphere?

The phrase appears in a note to the definition of “hazardous atmosphere” at 1910.146(b) and is meant to be an informational aid to employers and employees in approximating the lower flammable limits: “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.”

It should be noted that combustible dusts have differing lower flammable limits which are dependent on the composition of the dusts, the particle size, distribution and other factors. Since the airborne concentration may vary considerably within the space, and the settled dust may also pose hazards, it is important that the employer recognize the potential hazards when entering confined spaces containing such dust and that the employer take appropriate precautions for protection of entrants.

Regarding flammable dusts in confined space, it will be OSHA policy to sample and to analyze such dusts for combustibility, prior to issuing citations, whenever there is doubt as to the nature and extent of the dust hazard. Note that existing permissible exposure limits for nuisance dusts and other standards continue to apply.