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NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.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

August 8, 1994

Mr. David W. Spencer Baker Performance Chemicals, Inc. 3920 Essex Lane P.O. Box 27714 Houston, Texas 77227-7714

Dear Mr. Spencer:

This is in response to your June 16 letter requesting clarification of the Process Safety Management (PSM) of Highly Hazardous Chemicals (HHCs) standard, 29 CFR 1910.119 as it may apply to the batch chemical processes as described in the scenario below. Your question and our reply follow. Please accept our apology for the delay in responding.

Scenario: More than 10,000 pounds (4535.9kg) of flammable liquid, kept below its normal boiling point without benefit of chilling or refrigeration, is stored in an atmospheric tank. This flammable liquid is transferred by interconnected piping including temporary hosed to a blending unit. Before transfer, temporary hosed from the blending unit to other process units are disconnected. Also before transfer, the blending unit is rendered inoperative. After transfer of the flammable liquid to the blending unit is completed, the temporary hoses between the storage tank and the blending unit are disconnected. Subsequently, the temporary hoses between the blending unit and the other process units are connected and the blending unit is placed into operation. [The preceding scenario was amended for clarification during a August 3 telecon between you and Mr. Ron Davies of my staff.]

Question : Would the flammable liquid stored in the

atmospheric tank and transferred as described in the preceding scenario be considered a single process which would be excepted from PSM coverage by 29 CFR 1910.119(a)(1)(ii)(B)?

Reply: There is insufficient scenario information to answer your question. The following clarification is intended to assist you in determining whether your work site processes are covered by the PSM standard. The blending unit would have to meet the definition of atmospheric tank. The 1910.106 standard includes requirements for atmospheric tanks in which flammable liquids are stored. As such, the process which includes only the activities of flammable liquid storage and associated transfer between atmospheric tanks, that is, the storage tank and the blending unit, would be excepted from PSM coverage with the following exception. The flammable liquid atmospheric tanks and any separate vessels located nearby such that a highly hazardous chemical could be involved in a potential release are considered a single process (see the 1910.119(b) definition of "process"). When a separate vessel located nearby is part of another process which includes activities, that is handling, use, on-site movement or manufacturing in addition to storage and associated transfer activities, the 1910.119(a)(1)(ii)(B) exception would not apply.

If the work site employer intends to operate a process to avoid being subject to compliance with the PSM standard, it must have an effective program (and be prepared to demonstrate to the Occupational Safety and Health Administration (OSHA), that is, the Compliance Safety and Health Officer (CSHO) during an inspection of the work site, that such a program precludes a process, as described above, from being part of another process involving activities other than storage and associated transfer.

We appreciate your interest in occupational safety & health. If we may be of further assistance please contact us.


John B. Miles, Jr., Director Directorate of Compliance Programs