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NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.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

April 14, 1993

Mr. Shari Roney
Health and Safety Officer
Landlaw Environmental Services, Inc.
208 Watlington, Industrial Drive
Readsville, N.C. 27320

Dear Mr. Roney:

This is in response to your February 8 letter requesting interpretations of the Process Safety Management (PSM) of Highly Hazardous Chemicals standard, 29 CFR 1910.119. Please accept our apology for the delay in responding. Your questions and our responses follow:

Question 1: How high must the percentage of a chemical (listed in Appendix A of 1910.119) be to require compliance with the PSM standard?

Reply: The threshold quantities listed in Appendix A of the standard apply only to pure (or "chemical grade") chemicals unless otherwise specified, for example, Hydrogen Peroxide, 52% by weight or greater.

Question 2: Does Appendix A apply to compounds of the listed chemicals? If so, does the same percentage of solution apply to a compound?

Reply: Chemical compounds not listed as compounds in Appendix A are not covered by the PSM standard as toxic or reactive highly hazardous chemicals.

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


Roger A. Clark, Director
Directorate of Compliance Programs