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.

May 18, 1994

Mr. Robert A. Rusczek, President
264 Cottage Street
Springfield, MA 01104-3240

Dear Mr. Rusczek:

This is in response to your letter of April 13, 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 hydrofluoric acid.

You indicated that anhydrous hydrofluoric acid and hydrogen fluoride are both listed in Appendix A of the PSM standard with the same Chemical Abstract Number.

Anhydrous hydrofluoric acid and hydrogen fluoride are the same hazardous chemical. Aqueous solutions of hydrogen fluoride, for example 49% hydrofluoric acid and 51% water, would not be covered by the PSM standard.

It is important to note that inhalation of gaseous vapors of aqueous hydrofluoric acid can cause severe respiratory tract irritation that may be fatal. To prevent injury or illness, all contact with the acid must be avoided by the use of engineering controls and personal protective equipment.

In addition, hydrofluoric acid has a latency period. In concentrations greater than 50%, hydrofluoric acid burns are felt immediately, and tissue destruction is rapidly apparent. In concentrations of 20-50%, the burn becomes apparent 1-8 hours following the exposure, and in concentrations less than 20%, the pain and erythema can be latent for as long as 24 hours after the exposure. Latent symptoms can seriously delay proper treatment.

Anyone working with anhydrous or aqueous hydrofluoric acid should have received prior instruction about its hazards, and should know the recommended procedure for treatment in the event of exposure.

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


Raymond E. Donnelly, Director
Office of General Industry Compliance Assistance