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NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.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

June 22, 1993

Mr. F. L. Lambert
Environmental and
Technical Division
Westvaco-Chemical Division
Box 70848
Charleston Heights, S.C. 29415-0848

Dear Mr. Lambert:

This is in response to your April 30 letter requesting clarification of the Process Safety Management (PSM) of Highly Hazardous Chemicals (HHC's) standard, 29 CFR 1910.119. In your letter you specifically requested confirmation that, if HHC's which are listed without specified concentration limits in Appendix A of the PSM standard are at commercial grades less than 99 percent purity, the PSM standard is not applicable.

The substances listed in Appendix A without specified concentration limits are intended to be covered by the PSM Standard at commercial grade percentages of purity because the commercial grade of most of the HHC's is approximately 99 percent purity. Many of the HHC's, if not actually at 99% purity, are only one to two percent less than 99 percent pure. For example, the commercial grades of acrolein and allyl chloride are 97 percent purity. Some of these HHC's are considerably less than 99 percent pure. For example, the commercial grade of hydrogen fluoride is 70 percent (30% is pyridine).

Thank you for your interest in occupational safety and health. If we may be of further assistance please contact us.


Roger A. Clark, Director
Directorate of Compliance Programs

April 30, 1993

Mr. Roger A. Clark, Director
Directorate of Compliance Programs
U.S. Department of Labor
Occupational Safety
& Health Administration
200 Constitution Avenue, NW
Washington, D.C. 20210

Re: Applicability of 29 CFR 1910.119

Dear Mr. Clark:

Appendix A to 29 CFR 1910.119 contains a list of highly hazardous chemicals to which this standard applies. Some of the listed chemicals have specified concentration limits. Most of the listed chemicals have no specific concentration limits.

During a recent outreach workshop in Houston, Texas, Mr. Rollie Stroup of OSHA indicated that for those chemicals listed without specified concentration limits, the PSM Standard was not applicable if the concentration of the listed chemical was less than 99%.

I would suspect that the purity of commercial grades of many of the listed chemicals would be less than 99%.

I respectfully request your clarification of this issue.

Yours truly,

F. Lambert, Ph.D., P.E.
Environmental & Technical Director