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NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.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

March 21, 1994

Mr. David B. Smith
Central Soya Company, Inc.
1946 Westcook Road
P.O. Box 2507
Fort Wayne, Indiana 46801-2507

Dear Mr. Smith:

This is in response to your November 24, 1993 letter, requesting interpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals, 29 CFR 1910.119, standard. Please accept our apology for the delay in responding. Your questions and our responses follow.

Question 1:

Is 35 percent hydrochloric acid covered by the PSM standard?


No. Aqueous solutions of hydrogen chloride, that is, hydrochloric acid, are not covered by the PSM standard.

Question 2:

How do you determine whether an acid solution is covered by the PSM standard?


The PSM standard covers a workplace process containing a threshold quantity (TQ) or greater amount of highly hazardous (toxic, reactive, flammable or explosive) chemical. Some of the covered materials listed in Appendix A of the standard are acids with concentration thresholds listed. For example, a TQ or greater amount of perchloric acid (concentration greater than 60% by weight) is covered by the PSM standard. On the other hand, any amount of a perchloric acid at 60% or less concentration by weight would not be covered by the PSM standard.

In general, acids and other materials listed in Appendix A without threshold concentrations are covered at "commercial grade" concentration and higher. OSHA defines "commercial grade" as a typical maximum concentration of the chemical that is commercially available and shipped. The term "commercial grade" includes reagent grades. In cases where different maximum concentrations for commercial and reagent grades are typically shipped, the lower of the two maximum concentrations (and any concentration greater) is intended to be covered by the PSM standard. In order to determine the covered concentration, reference may be made to any published catalogue of chemicals for commercial sales. To determine the correct entry(s) in the catalogue, reference must also be made to the Chemical Abstract Service (CAS) number listed in Appendix A of the PSM Standard.

In addition to the above, a TQ, that is, 10,000 pounds (4535.9 kg) of a flammable liquid (including mixtures, consisting of acids or otherwise), is covered by the PSM standard. Also, the manufacture of any amount of an explosive, as defined in 29 CFR 1910.109, including mixtures consisting of acids or otherwise, is 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.


H. Berrien Zettler, Deputy Director
Directorate of Compliance Programs