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 http://www.osha.gov.

June 24, 1993

Mr. Jon LaRue
Nova Engineering, Inc.
5727 So. Lewis,
Suite 300
Tulsa, Oklahoma 74105

Dear Mr. LaRue:

This is in response to your May 17 letter, requesting an interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals standard, 29 CFR 1910.119. Specifically, you requested that the Occupational Safety and Health Administration clarify that sulfuric acid is not covered by the PSM standard.

Sulfuric acid, which contains 93 to 98 percent H(2)SO(4) and the remainder is water, is not covered by the PSM standard. Please note that Oleum (65-80 percent by weight, also called Fuming Sulfuric Acid), which is listed in Appendix A of the PSM standard, is in error. A workplace process which contains a threshold quantity of 1000 pounds (453.6 kg) or more of Fuming Sulfuric Acid (65% by weight or greater Sulfur Trioxide SO(3), is covered by the PSM standard. This percentage change in concentration will be the subject of editorial changes to the PSM standard anticipated in the near future.

Thank you for your interest in occupational safety and health. If we may be of further assistance please contact us.


Roger A. Clark, Director
Directorate of Compliance Programs