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.

May 27, 1993

Mr. Wayne Geyer
Executive Vice-President
Steel Tank Institute
570 Oakwood Road
Lake Zurich, Illinois 60047

Dear Mr. Geyer:

This is in response to your letter of December 28, 1992, in which you requested from the Occupational Safety and Health Administration (OSHA) an interpretation on whether the use of double-wall, above-ground tanks is acceptable for secondary containment of flammable and combustible liquids, in place of diking, to meet the requirements of 29 CFR 1910.106(b)(2)(vii). Please excuse the delay in our response.

This request is a follow-up to your September 30, 1992, meeting with Mr. James C. Dillard, of my staff, and Mr. James J. Concannon, former Director, Office of Variance Determination. At that meeting, Mr. Dillard informed you and members of your delegation that your original request for an interpretation of 1910.106(b)(2)(vii) would have to await the results of the meeting of the National Fire Protection Association (NFPA) 30 Committee, which met on December 2-4, 1992, to address, among others items, this particular issue.

The NFPA 30 Committee recommended acceptance of the need to recognize secondary containment of tanks as a form of spill control, and its recommendation was published in the NFPA's 1993 Annual Meeting, Technical Committee Documentation publication. The committee stated that aboveground secondary- containment-type tanks need not meet the remote impounding and the diking requirements of NFPA 30 if the following conditions are met:

(a) Tank capacity cannot exceed 12,000 gallons.

(b) All piping connections to the tank must be made above the normal maximum liquid level.

(c) Means must be provided to prevent the release of liquid from the tank by siphon flow.

(d) A means must be provided for determining the level of liquid in the tank, and it must be accessible to the delivery operator.

(e) Overfilling must be prevented by sounding an alarm when the liquid level in the tank reaches 90% of capacity and by automatically stopping delivery of liquid to the tank when liquid level reaches 95% of capacity. These provisions must not restrict or interfere with the proper functioning of the normal or emergency vent.

(f) Spacing between adjacent tanks must not be less than 3 ft.

(g) The tanks must be capable of resisting damage from impact of a motor vehicle or suitable collision barriers must be provided.

(h) Enclosed interstitial space must be provided with emergency venting in accordance with 2-3.6.

If NFPA adopts as planned, at its May, 1993 Annual meeting, exception No.2, NFPA 30, 1990, Paragraph 2-3.3, then OSHA will follow its established compliance policy of addressing violation of 1910.106(b)(2)(vii) as de minimis if the eight above- listed conditions are met. (The de minimis policy accepts employer's compliance with a proposed standard or amendment or a consensus standard rather than with the standard in effect at the time of the inspection, provided that the compliance provides equal or greater employee protection.)

If we can be of further assistance, please feel free to contact Mr. Dillard at (202) 219-8031.


Roger A. Clark, Director
Directorate of Compliance Programs