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 30, 1991

Mr. Ken Cooper
Regional Safety Manager
United States Department of
the Interior Fish and Wildlife Service
75 Spring Street, S.W.
Atlanta, Georgia 30303

Dear Mr. Cooper:

Thank you for your letter of June 27, requesting determination as to whether ConVault aboveground tanks are required to be diked to comply with the 29 CFR 1910.106(b)(2)(vii) standard on storage of flammable liquids. Also, you asked whether ConVault tank systems have a variance from the diking requirement.

The intent of 29 CFR 1910.106(b)(2) is to provide for employee safety from exposure to fire and explosion hazards associated with aboveground storage of flammable and combustible liquids. Diking would not be required when the following provisions are satisfied by the employer who uses ConVault vaulted aboveground tanks to store flammable liquids. The employer shall undertake a monitoring program acceptable to the Occupational Safety and Health Administration (OSHA), which incorporated the capabilities provided with the ConVault vaulted aboveground tank to detect leakage between the primary, that is, the inner steel tank and the secondary, that is, outer, reenforced concrete shell enclosures. Also the employer shall provide effective means, acceptable to OSHA, which prevents spillage from overfilling and/or overflowing due to local changes in temperature.

To date, OSHA has not provided a variance to an employer to use a ConVault vaulted aboveground tank to store flammable liquids without diking required by 29 CFR 1910.106(b)(2)(vii). OSHA variance regulations apply primarily to employers whose employees may be exposed to hazards related to a product, and do not normally apply to the manufacturer of a product unless the manufacturer's employees are also exposed.

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


Gerard F. Scannell
Assistant Secretary