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.

November 15, 1993

Mr. Trey Mayfield
Can Manufacturers Institute
1625 Massachusetts Avenue, N.W.
Washington, D.C. 20036

Dear Mr. Mayfield:

This is in response to your letter of August 30, concerning the Permit-Required Confined Space (PRCS) standard (1910.146) and a work practice in your Industry. Specifically you are seeking confirmation that the work practices outlined in your letter would constitute compliance with 1910.146(c)(7). Please accept our apology for the delay in this response.

Metal container curing ovens meet the definition of a PRCS. Therefore, employee entry into such spaces must be conducted in compliance with the PRCS standard. An employer who eliminates the hazards from a permit space, as provided by paragraph (c)(7) of the standard, can reclassify that space as a non-permit confined space. That reclassification, which would remain in effect as long as the hazards remain eliminated, would allow employers to have employees enter the curing ovens without implementing a permit space program.

Item 1 of your letter addresses using Lockout-Tagout (1910.147) procedures to eliminate the hazards of moving machinery and natural gas. We agree that through the application of 1910.147, the hazards of stored energy and moving machinery would be eliminated. We do not agree that lockout-tagout would eliminate the natural gas hazard. Hazard elimination in that case would require one of the techniques (blanking, blinding, misaligning or removing sections of lines or pipe, and double block and bleed system) referenced in the definition of "isolation" (see paragraph (b) of 1910.146).

Item 2 indicates that a cool down time is allotted so that the latent heat of the oven does not create a heat exposure hazard. We concur with the cool down practice to eliminate this heat stress potential. However, we suggest the actual job safety practice indicate a maximum oven temperature allowable or other measurable parameter (period of time) allotted before entry.

Item 3 describes your process for verifying that there are no atmospheric hazards. The standard does not specify a duration of time over which verification monitoring must be done. However, we do not see a problem with the documented baseline monitoring program being conducted over an 8 hour period of time as long as the employer can prove that atmospheric hazards have been eliminated from the ovens before an employee enters. Verification monitoring with the ventilation system off will be needed to establish that atmospheric hazards have been eliminated. OSHA agrees that spot air monitoring for atmospheric monitoring for atmospheric hazards is not necessarily required by paragraph (c)(7), however, it is the most appropriate way of determining that atmospheric hazards have not manifested themselves.

Item 4 prohibiting solvents or welding during non-permit entries is a sound practice and should be continued.

Should you have further questions concerning your request please contact Mr. Don Kallstrom in the Office of General Industry Compliance Assistance (202) 219-8031.


Roger A. Clark, Director
Directorate of Compliance Programs