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NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.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

January 31, 1994

Mr. Donald J. Connelley
Process Safety Specialist
Central Engineering Department
AKZO Chemicals Inc.
9 Livingstone Avenue
Dobbs Ferry, New York 10522-3409

Dear Mr. Connelley:

The purpose of this letter is to correct a misinterpretation of the Process Safety Management (PSM) of Highly Hazardous Chemicals standard, 29 CFR 1910.119 in our September 9 letter to you. The corrected interpretation follows.

Except for the mixtures specifically listed in Appendix A (e.g., Chloropicrin and Methlyl Bromide and of Chloropicrin and Methyl Chloride), toxic or reactive chemical mixtures which are not explosive and which are not flammable liquids or gases are not covered by the PSM standard. Therefore, mixtures of Tertiary-Butyl Hydroperoxide (TBHP) and of Cumene Hydroperoxide and non-flammable organic solvents are not covered by the PSM standard.

Please note that there are no Chemical Abstract Service (CAS) numbers assigned to chemical mixtures. Other highly hazardous chemicals listed in Appendix A are further identified by unique CAS numbers. CAS numbers are assigned only to chemicals which are chemically reactive or chemically coordinated.

By 29 CFR 1910.1200(g) of the Hazard Communication Standard, chemical manufacturers and importers must develop or obtain a material safety data (MSD) sheet for each hazardous chemical they produce or import. Also, this standard requires that employers must have a MSD sheet for each hazardous chemical which they use in the workplace. These MSD sheets should be referenced to identify chemicals and if included, their CAS numbers. Also, when using other references, for example, a chemical manufacturer's sales catalog, the CAS number associated with a particular chemical should be noted. Both the name of the chemical and its corresponding CAS number should be used to determine whether a particular chemical, intended for use or used in the workplace, is listed in Appendix A.

Please disregard and discard the earlier correspondence. Thank you for your interest in occupational safety and health. If we can be of further assistance, please contact us.


Roger A. Clark, Director
Directorate of Compliance Programs