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.

June 3, 1994

Mr. Kenneth W. Clarfield
Director - Member Services
Private Label Manufacturers Association
369 Lexington Avenue
New York, New York 10017

Dear Mr. Clarfield:

This is in response to your February 2 letter, requesting interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals standard, 29 CFR 1910.119. Specifically, you requested clarifications as to whether the PSM standard would be applicable to three scenarios on processes involving flammable liquids. Please accept our apology for the delay in responding. Your scenarios and our replies follow.

Scenario #1

An exterior (or underground) atmospheric storage tank containing more than 10,000 pounds (4535.9 kg) of a flammable liquid is connected by piping to a smaller interior atmospheric tank with a capacity of more than 10,000 pounds. Batch quantities of the flammable liquid are transferred to the interior tank, diluted with water and/or other ingredients such as flavors and fragrances, and agitated to blend. From the interior tank, the mixture is filled into consumer containers, generally plastic bottles. Throughout, the flammable liquid and the finished product are subjected only to ambient temperatures by which they are maintained well below their normal boiling points without benefit of chilling or refrigeration.


This scenario would be covered by the PSM standard. The mixing activity of this process cancels the exception at 29 CFR 1910.119(a)(ii)(B) which allows only storage and associated transfer as excepted activities.

Scenario #2

This scenario is exactly the same as #1 above, except that the interior tank has a capacity of less than 10,000 pounds.


This scenario would be covered by the PSM standard. The mixing tank, the piping to the storage tank and the storage tank are all considered parts of a single process (See 1910.119 (b) definition) which contains a threshold quantity or more of flammable liquid. Also, the reply to scenario #1 applies.

Scenario #3

Interior portable storage tanks each contain less than 10,000 pounds of a flammable liquid, but totaling more than 10,000 pounds in the aggregate. [Per your clarification on February 25 by telecon with Mr. Ron Davies of my staff, these storage tanks are filled by hose connection from commercial tank motor vehicles (CTMVs) delivering flammable liquids at an above ground dock.] The portable tanks are not interconnected. One portable tank at a time is connected by flexible hose to:

a) a bottle filling machine which dispenses the liquid into consumer containers (generally plastic bottles), or

b) an atmospheric interior tank of less than 10,000-pound capacity where other ingredients such as colors, flavors and fragrances are blended in with agitation. From the interior tank the mixture is transferred through piping to a bottle filling machine where it is filled into consumer containers (generally plastic bottles).

[Per your clarification by a April 19 telecon with Mr. Ron Davies of my staff, you disclosed that workplace installations described in (a) and (b) above are located in close proximity to each other in the same facility].


This scenario would be covered by the PSM standard. By the definition of process, the interior portable storage tanks and mixing tank would be considered a single process since they either are connected by piping or are unconnected and located in close proximity to each other such that the flammable liquids in these tanks could be involved in a potential release.

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


Raymond E. Donnelly, Director
Office of General Industry Compliance Assistance