October 12, 1990

Ms. Tanja Petranovic
McKenna, Conner and Cuneo
1575 Eye Street, N.W.
Washington, D.C. 20005

Dear Ms. Petranovic:

Thank you for your letter of August 16, regarding the requirements of the Occupational Safety and Health Administration's (OSHA) Hazard Communication Standard (HCS), 29 CFR 1910.1200. Specifically, you requested guidance regarding the standard's material safety data sheet (MSDS) requirements for residues in a mixture, and posed the following question:

" Chemical A and Chemical B are reacted to form Mixture C. Mixture C contains a residue of Chemical A. Chemical A, which is a carcinogen, is present as a residue in the mixture at less than .1%. Is an MSDS required for Chemical A?"

In order to ensure we are using the correct terms, we are restating your question slightly as follows: Substance A and Substance B are reacted to form Substance C. However, a residual of Substance A remains after the reaction occurs. Therefore, the new product is Substance C, plus less than 0.1% of Substance A, or Mixture D. Would information on the hazards of Substance A be required on the MSDS for Mixture D? Given that Substance A constitutes less than 0.1% of Mixture D, the answer would generally be no. The exceptions would be if, under paragraph (d)(5)(iv) of the HCS, you perform a hazard determination and find there is evidence that the chemical can still present a health hazard to workers in that concentration, or that it could be released and exceed established permissible exposure limits or threshold limit values. In these situations, information regarding Substance A would have to be included on the MSDS for Mixture D. I hope this discussion has been helpful to you. Please feel free to contact us again if we can be of further assistance.

Keep your reactions well-stirred with stirrers from Safety Emporium.

Patricia K. Clark
Director Designate
Directorate of Compliance Programs

August 16, 1990

Ms. Patricia Clark
Director of Compliance Programs (N3469)
Occupational Safety
and Health Administration
200 Constitution Avenue, N.W.
Washington, DC 20210

Re: Reporting Requirements for Residues in a Mixture

Dear Ms. Clark:

We are requesting guidance regarding Material Safety Data Sheets (MSDSs) for residues in a mixture. We would appreciate the Agency's response to the following question.

Chemical A and Chemical B are reacted to form Mixture C. Mixture C contains a residue of Chemical A. Chemical A, which is a carcinogen, is present as a residue in the mixture at less than .1%. Is an MSDS required for Chemical A?

I have previously conferred with Jennifer Silk on this issue and she indicated that an MSDS would probably not be required for Chemical A. We are requesting confirmation of this interpretation.

Yours sincerely,

Tanja Petranovic

TP:bas