An atmosphere that may expose workers to the risk of death, incapacitation, injury, acute illness,
or self-rescue impairment from one or more of the following causes: (1) flammable gas, vapor, or
mist in excess of 10 percent of its lower flammable limit (LFL); (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 [1.5 m] or less.); (3)
atmospheric oxygen concentration below 19.5 percent or above 23.5 percent; (4) atmospheric
concentration of any substance for which a dose or a permissible exposure limit is published in 29
CFR 1910 Subpart Z, Toxic and Hazardous Substances, which could result in employee exposure
in excess of its dose or permissible exposure limit; (5) any other atmospheric condition that is
immediately dangerous to life or health.) (NOTE: For air contaminants for which OSHA has not
determined a dose or permissible exposure limit, other sources of information, such as material
safety data sheets, published information, and internal documents can provide guidance in
establishing acceptable atmospheric conditions.)
