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.

September 27, 1994

Mr. Michael Kohlhauff Director of Quality Systems Sperry - Sun Drilling Services 3000 North Sam Houston Pkway East (77032) P.O. Box 60070 Houston, Texas 77205

Dear Mr. Kohlhauff:

This is in response to your May 17 letter, requesting clarification of the Process Safety Management (PSM) of Highly Hazardous Chemicals (HHCs) standard, 29 CFR 1910.119 as it may apply to more than 250 pounds (110.9kg) of thionyl chloride stored on your work site as further described in the scenario below. Your question and our response follows. Please accept our apology for the delay in responding.

Scenario: Sperry-Sun has a manufacturing assembly operation which involves the fitting of final articles into oilfield service equipment. One of the articles employed in the assembly process is a cell that, inter alia, contains thionyl chloride. These cells are manufactured by another company and purchased by Sperry-Sun. Each cell contains the following amounts of thionyl chloride


CC cell 0.09 pounds (41.5 grams) thionyl

chloride 3/2C cell 0.07 pounds (31.5 grams) thionyl chloride AA cell 0.01 pounds (4.7 grams) thionyl chloride

The total cell count kept in on-site storage by Sperry-Sun yields a total thionyl chloride weight in excess of the 250 pound (110.9kg) threshold quantity (TQ) listed in Appendix A of the PSM standard as a covered HHC. Sperry-Sun does not have interconnected vessels, but rather small, hermetically sealed "vessels", each containing less than or equal to 0.09 pounds (41.5 grams) of thionyl chloride. Sperry-Sun never removes the thionyl chloride from the cells, and Sperry's supplier of the cells delivers them in a hermetically sealed condition so that thionyl chloride never contacts anything during assembly operations. Rather, the sealed cells themselves are part of the assembly of the oilfield service equipment.

Question: Would the work site scenario as described above be covered by the PSM standard?

Reply: There is insufficient scenario information to determine whether the thionyl chloride process at your work site is covered by the PSM standard. The following clarification is intended to assist you in this determination. Storage of a TQ or greater amount, that is 250 pounds (110.9kgs) or more, of thionyl chloride at one location on a work site is covered by the PSM standard. The activity of storage alone or associated with other activities, including use, handling, on-site movement or manufacturing of an HHC constitutes a "process" as defined in 1910.119(b). Also by this definition, a process, such as your manufacturing assembly operation involving thionyl chloride vessels and a storage process, such as described above, which are located such that a HHC, such as thionyl chloride, could be involved in a potential release would be considered a single process.

As noted in the preamble of the Final Rule, a copy of which is enclosed for your use, an employer may disperse storage of the HHC in amounts which would not exceed the TQ, and segregate storage and other processes such that a release from one work site location would not cause a release from others around the work site. Alternatively, an employer could order, more frequently, smaller shipments of HHC so that there is less than a TQ at the work site at any one point in time.

We appreciated your interest in occupational safety and health. If we can be of further assistance, please contact the Office of General Industry Compliance Assistance, Ronald Davies on 202-219-8031 extension 110.


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