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.

January 28, 1994

Mr. Gerald W. Lancour, Director
Safety, Health & Environmental Affairs
McDonnell Douglas
P.O. Box 516
Saint Louis, MO 63166-0546

Dear Mr. Lancour:

This is in response to your letter of October 1, requesting interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals, 29 CFR 1910.119 standard. Specifically you requested clarification as to whether the PSM standard applies to aqueous solutions of Hydrogen Fluoride.

Hydrogen fluoride and anhydrous hydrofluoric acid, both listed in Appendix A of the PSM standard, are the same highly hazardous chemical. Aqueous solutions of hydrogen fluoride, for example, 70 percent hydrofluoric acid and 30 percent water, would not be covered by the PSM standard.

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