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.

February 5, 1992

Mr. Donald J. Connolley
Central Engineering Department
Akzo Chemicals Inc.
Livingstone Avenue
Dobbs Ferry, New York 10522-3401

Dear Mr. Connolley:

Thank you for your letter of November 6, 1991 requesting interpretations and clarifications of 29 CFR 1910.106 standards on outside, above ground, tanks used for storage of flammable and combustible liquids. Responses to your questions follow. Please accept our apology for the delay in our response.

Question 1: Is the scope of 29 CFR 1910.106 intended to

be limited to the storage of non-reactive flammable and combustible liquids at low pressure (less than 15 psig), or is this standard applicable to these liquids regardless of system pressure?

Reply: The standards at 29 CFR 1910.106 apply to stable as well as unstable (reactive) combustible and flammable liquids as defined in paragraph 1910.106(a). The standards at paragraph 1910.106(b) apply to atmospheric tanks, low pressure tanks and pressure vessels, as defined in paragraph 1910.106(a) for tank storage of combustible and flammable liquids in the workplace. Pressure vessels which are designed, constructed, installed, operated and maintained in compliance with paragraph 1910.106(b) shall be used to store combustible and flammable liquids at (1.05 kilograms per square centimeter) gauge (p.s.i.g.).

Question 2: If the scope of 29 CFR 1910.106 is not limited

to a given system pressure range, is the method for sizing emergency relief devices for the storage of non-reactive materials at pressures above 15 psig presented in API-520 acceptable to meet the requirements of 29 CFR 1910.106? If API-520 is considered by OSHA to not meet these requirements, then I recommend OSHA and industry experts meet to discuss the issue and resolve the discrepancies.

Reply: Installation of emergency relief venting for outside, above ground, tanks used to store combustible and flammable liquids in the workplace shall comply with paragraph 1910.106(b)(2)(v). Use of emergency relief venting predicated on sizing required to comply with American Petroleum Institute (API) standard, API RP-520 in place of emergency relief venting which complies with the capacity requirements of paragraph 1910.106(b)(2)(v) is subject to Occupational Safety and Health Administration (OSHA) consideration as a variance. Should you choose to pursue a variance, please refer to the enclosed copy of 29 CFR 1905. Section 1905.11 delineates the criteria necessary to obtain a permanent variance. With respect to paragraph 1910.106(b)(2)(v) requirements, you must demonstrate that the emergency relief venting sized to comply with API RP-520 provides equal or greater protection to employees from fire and explosion hazards in the workplace. Your application should be forwarded to:

Occupational Safety and Health Administration Office of Variance Determination, Room N3651 200 Constitution Avenue, N.W. Washington, D.C. 20210

We appreciate your interest in employee safety and health. If we can be of further assistance, please do not hesitate to contact us.


Patricia K. Clark, Director
Directorate of Compliance Programs