May 18, 1994

Mr. Robert A. Rusczek, President
Envirocomp
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.

Sincerely,



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