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 30, 1999

Mr. Robin J. Eddy
Regulatory Compliance Manager
Allied Universal Corporation
8350 N.W. 93 Street
Miami, FL 33166-2098

Dear Mr. Eddy:

Thank you for your inquiry of October 29, 1998, requesting clarification on the Occupational Safety and Health Administration (OSHA's) Permit-required Confined Spaces standard 29 CFR 1910.146. We regret the delay in responding to your request.

You indicated that you have evaluated your facility and determined that the Sodium Hydoxide and Sodium Hypochlorite above ground tanks are permit-required confined spaces. Your question is, "Do we have to test for flammable vapors if no such hazard exists in the sodium hydroxide and sodium hypochlorite above ground tanks?" You also indicated that based upon information regarding the two chemicals, both are non-flammable, and produce no flammable vapors.

The type of testing that needs to be performed within a permit-required confined space is dependant on the hazards that are present within the space; employers are not required to test substances which will not potentially be present. As paragraph (d)(5)(ii)of 29 CFR 1910.146 states:

(ii) Test or monitor the permit space as necessary (emphasis added) to determine if acceptable entry conditions are being maintained during the course of entry operations;

Please note that the order of testing given in paragraph (d)(5)(iii) is important. Many devices depend on the presence of adequate oxygen to give accurate results.

If the elimination of a pre-entry test causes changes in your current permit-space program, then employees must be trained on the changes to the program, including the reasons for the change. Also, if some spaces will be entered where a test for flammables will still be needed, these spaces will need to be clearly identified to employees, and employees will need to be trained on the differences between the two types of permit-spaces.

Thank you for your interest in occupational safety and health. If you have any further questions, please contact Mr. Wil Epps or Mr. Patrick Kapust at (202) 693-1850.


Richard Fairfax, Director
Directorate of Compliance programs