Archive Notice - OSHA Archive

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

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

December 1, 1992

Mr. Kevin S. Sall
Manager, Hazardous Materials
National Paint & Coatings Association
1500 Rhode Island Avenue, N.W.
Washington, D.C. 20005-5597

Dear Mr. Sall:

This is in response to your letter of June 16, addressed to Mr. Thomas Seymour, Deputy Director of Safety Standards Programs, requesting an interpretation of the Occupational Safety and Health Administration's (OSHA) Process Safety Management (PSM) standard, 29 CFR 1910.119. Please accept our apology for the lateness of this reply.

You specifically asked about the applicability of the PSM standard to typical processes in a paint manufacturing facility, which include the mixing and blending of flammable liquids with other raw materials, and which typically involve few or no chemical reactions. You stated that the flammable products are processed below their normal boiling points and that several large batch vessels are located near each other, with an aggregate weight above the threshold quantity of 10,000 pounds (4535.9 kilograms).

The requirements of the PSM standard would apply to such operations. The exemption provided in the standard at 29 CFR 1910.119(a)(1)(ii)(B) for situations involving flammable liquids applies only when such liquids are being stored in atmospheric tanks (where the tank pressure does not exceed 0.5 pounds per square inch gauge [p.s.i.g])or transferred and the liquids are kept below their normal boiling point without benefit of chilling or refrigeration. This exemption does not apply to a mixing and blending operation related to paint manufacturing.

You also inquired about a section of the PSM standard's non mandatory Appendix C, which suggests that, if reduced inventory of highly hazardous chemicals is not feasible, an employer might consider dispersing inventory to several locations on-site. You asked for guidance on when such materials are to be considered part of a single process, and on evaluation techniques to determine adequate separation distances.

Under the definition of "process" provided at 29 CFR 1910.119(b), any group of vessels which are interconnected and separate vessels which are located such that a highly hazardous chemical could be involved in a potential release shall be considered a single process. Inventories of highly hazardous chemicals would not be considered to be adequately dispersed if the storage vessels are connected with or in proximity to a covered process such that they could be involved in a potential release.

OSHA has not developed, nor is it aware of, any standard evaluation technique to determine adequate distances to separate chemical inventories. If an employer chooses to disperse highly hazardous chemicals on-site, the separation distances would have to be determined on a case-by-case basis, considering such factors as the nature of the chemicals and covered processes, total inventories, threshold quantities of pertinent chemicals, and facility layout.

We hope this information is helpful to you and we regret the delay in providing you with this clarification.


Roger A. Clark,
Directorate of Compliance Programs