PSM: OSHA clarifies stance on aqueous solutions of highly hazardous chemicals

LOI explains a significant part of the new policy

Posted July 28, 2016

OSHA recently published a new Letter of Interpretation (LOI), Process Safety Management of Highly Hazardous Chemicals and Covered Concentrations of Listed Appendix A Chemicals. The document rescinds and replaces the document of the same title dated June 5, 2015. It clarifies the earlier document, provides additional guidance, and incorporates a new interim citation policy.

The LOI discusses a significant part of the new policy:

OSHA notes that where an entry in Appendix A is listed as “anhydrous,” it does not cover aqueous solutions or aqueous mixtures. Anhydrous means “containing no water” or “without water.” Thus, by definition, Appendix A to PSM does not cover aqueous solutions or aqueous mixtures of chemicals specifically listed as “anhydrous.”

In addition, although not specifically designated as “anhydrous,” OSHA has interpreted Appendix A to mean that the PSM standard does not cover Hydrogen Chloride (CAS 7647-01-0) and/or Hydrogen Fluoride (CAS 7664-39-3) in aqueous solutions or aqueous mixtures.

Therefore, the following entries in Appendix A are not covered when in aqueous solutions or aqueous mixtures:

  1. Ammonia, Anhydrous (CAS 7664-41-7)7;
  2. Dimethylamine, Anhydrous (CAS 124-40-3);
  3. Hydrogen Cyanide, Anhydrous (CAS 74-90-8);
  4. Methylamine, Anhydrous (CAS 74-89-5);
  5. Hydrochloric Acid, Anhydrous/ Hydrogen Chloride (CAS 7647-01-0); and
  6. Hydrofluoric Acid, Anhydrous/ Hydrogen Fluoride (CAS 7664-39-3).

In such cases, the listing in Appendix A covers only the anhydrous form of the chemical.

Furthermore, OSHA finds that aqueous mixtures of hydrogen bromide (at concentrations below 63 percent) and mixtures of alkylaluminum (at any concentration) will fall within the partial pressure exemption under all normal handling and storage conditions.

This article was written by Travis Rhoden of J. J. Keller & Associates, Inc.


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