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NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.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

April 30, 1999

MEMORANDUM FOR:    KENNETH W. GERECKE, Assistant Regional Administrator
                   Region III

FROM:              RICHARD FAIRFAX, Director
                   Directorate of Compliance Programs Assistance

SUBJECT:           PSM Applicability to a 50% Solution of Hydroxylamine

This is in response to your March 17, 1999 memorandum, to Herb Washington, Director, OSHA -- Office of General Industry Compliance on the applicability of the Process Safety Management of Highly Hazardous Chemicals; Explosives and Blasting Agents (29 CFR 1910.119) to a 50% solution of hydroxylamine.

Question 1: What is the commercial grade of hydroxylamine that would invoke coverage of the PSM standard?

Response: Highly hazardous chemicals listed in Appendix A of the PSM standard without specified concentration limits, such as hydroxylamine (CAS #7803-49-8), are intended to be covered by the PSM standard at commercial grade percentages. OSHA defines commercial grade as a typical maximum concentration of the chemical that is commercially available and shipped. The maximum concentration is an assay or nominal value which can vary ± percentages depending on the manufactures' or distributors' specifications.

The Aldrich -- Catalog Handbook of Fine Chemicals, 1998-1999, lists the maximum commercial grade concentration for hydroxylamine as a 50 weight % (50%) solution. Aldrich specifications for 50% hydroxylamine solution can vary ± 5%. Additionally, of the three known manufacturers of hydroxylamine, the maximum concentration produced is a 50% solution, therefore, it is the maximum concentration commercially available and shipped. Given the above, a 50% hydroxylamine solution is covered by the PSM standard. If a process is designed and intended to, or in fact does, contain a threshold quantity (2,500 pounds) or greater of a 50% hydroxylamine solution then the process is covered by PSM.

Question 2: A September 11, 1995 letter from John B. Miles, Director, OSHA's Directorate of Compliance Programs to Mr. Jeffery Brown, R.W. Greef & Co., Inc., states, "Assuming the commercial grade of the liquid form (hydroxylamine) is near 99% concentration, a 50% solution would not be covered by the standard." Is this a correct statement, if not, what is the maximum commercial grade concentration for hydroxylamine?

Response: OSHA has not changed its position relative to determining PSM coverage based on the maximum commercial grades of Appendix A materials. The September 11, 1995 OSHA response was technically correct because it was based on the assumption that the maximum commercial grade concentration of hydroxylamine was 99%. If that assumption were correct, a 50% solution of hydroxylamine would have been a non-covered material. In the R.W. Greef OSHA response, the "assumption" was intended to be part of an example methodology for employers to use to determine if an Appendix A material is covered by PSM based on its concentration. However, the assumed 99% maximum commercial grade concentration was not a correct value.

The maximum commercial grade concentration of hydroxylamine is, in fact, 50%. Therefore, a 50% hydroxylamine solution is covered by the PSM standard.

If you have any questions, please contact Mike Marshall in OSHA's Office of General Industry Compliance Assistance at (202) 693-1850.