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.

July 7, 2000

Mr. Rafael E. Romero, P.E.
Galloway, Romero & Associates
5350 DTC Parkway
Englewood, Colorado 80111-3006

Dear Mr. Romero,

Thank you for your letters dated December 7,1999, and February 14, 2000, to the Occupational Safety and Health Administration's (OSHA's) Regional Office in Denver, Colorado. Your letters have been referred to the Directorate of Compliance Programs.

You requested an interpretation of 29 CFR 1910.106, Flammable and Combustible Liquids, and a possible reduction in the minimum separation distance for above ground tanks, warehouses, and other plant buildings. You also requested approval to reduce the separation distance for Class I liquids from the 25 foot requirement to 12.5 feet based on your double-wall tank design. You stated in your letter that the local fire department gave you a permit for a reduction in distance from 25 feet to 20 feet.

Based on the information we received, at this time we cannot approve a reduction of the minimum safety distance described in 1910.106(f)(3)(i). We referenced the most current National Fire Protection Agency (NFPA) guidelines in reviewing our requirements. In the latest edition of the NFPA 30, Flammable and Combustible Liquid Code, 1996 edition, article 5-6.3.1 states that the separation distance of 25 feet for Class I liquids may be reduced "if there is suitable protection for exposures." The appendix to this section further clarifies: "Use of fixed fire protection systems, dikes, fire-rated barriers, or a combination of any of these can provide suitable protection from exposures." However, this does not explicitly approve the sole use of double-wall tanks as a means of protection from exposures. Based on the information you provided in your letter, coupled with the slight reduction in distance from your local fire department, we cannot approve a reduction as low as 12.5 feet.

In addition, although in the information we received double-wall tanks appeared to have a greater safety factor than single-wall tanks, the use of double-wall tanks does not exempt the employer from the specified safety distances that are outlined in 1910.106(f)(3)(i): 25 feet for Class I liquids and 15 feet for Class II and III liquids. This separation is primarily required to increase the chance of controlling a fire originating in a tank vehicle before it spreads to other properties.

If you wish to further pursue an assessment to reduce the current required distance, we suggest that you apply for a variance. The request can be sent to:

[Office of Technical Programs and Coordination Activities
Room N3655, 200 Constitution Ave., N.W.
Washington, DC 20210
Phone: (202) 693-2110]

Thank you for your interest in occupational safety and health. We hope you find this information helpful. Please be aware that OSHA's enforcement guidance is subject to periodic review and clarification, amplification, or correction. Such guidance could also be affected by subsequent rulemaking. In the future, should you wish to verify that the guidance provided herein remains current, you may consult OSHA's website at http://www.osha.gov. If you have any further questions, please feel free to contact the [Office of General Industry Enforcement at (202) 693-1850].


Richard E. Fairfax, Director
[Directorate of Enforcement Programs]

[Corrected 6/2/2005]