OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

March 26, 1999

Mr. Marc A. Viera
SAGE Environmental, Inc.
44 East Avenue
Suite 209
Pawtucket, RI 02860

Dear Mr. Viera:

This is in response to your letter of March 3, 1999, requesting clarification on the note following the definition of a "hazardous atmosphere" as found in 29 CFR 1910.146(b). Your question has been restated as follows:

If a confined space has an atmospheric concentration of a Subpart Z contaminant over its Permissible Exposure Limit (PEL); but it is not capable of causing death, incapacitation, impairment of ability to self-rescue, injury, or acute illness; would this atmosphere meet the definition of a "hazardous atmosphere"?

Response: The preamble to the Permit Required Confined Space standard (Federal Register January 14, 1993, Volume 58, No. 9, page 4474) clearly states that an atmosphere that contains a substance at a concentration exceeding a permissible exposure limit intended solely to prevent long-term adverse health effects is not considered to be a hazardous atmosphere on that basis alone. Therefore, if the atmosphere is above the PEL, then it would not automatically be classified as a "hazardous atmosphere".

If you have further questions on this response, please contact Mr, Patrick Kapust or Mr. Wilfred Epps of my staff at 202-693-1850.


Richard Fairfax, Director
Directorate of Compliance Programs