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 https://www.osha.gov.

October 16, 1991



SUBJECT: Hazard Determinations under the HCS for Sodium Hypochlorite


This is response to your memorandum of August 22, regarding the appropriateness of a hazard determination performed by Jones Chemical, Inc., for sodium hypochlorite. This issue arose during the investigation of a non-formal complaint by the Buffalo Area Office in which the complainant disagreed with the hazard determination performed by Jones Chemical. That company had found there to be insufficient evidence to list sodium hypochlorite as a potential mutagen on the MSDS.

The determination regarding mutagenicity was based on in vitro studies (Ames/Salmonella and Chinese hamster fibroblast tests, ref.: M. Ishidate Jr., et.al., 1984, Food and Chemical Toxicology, and Meier et.al., 1985, Environmental Mutagenesis) and subsequent review of these data by several toxicologists. Based on the method of testing, the company concluded that a determination of mutagenicity was not warranted, and they did not include mutagenic data on their MSDS for sodium hypochlorite. Other sources of information on sodium hypochlorite, for example, the New Jersey Department of Health's "Hazardous Substance Fact Sheet" for sodium hypochlorite, indicates that this chemical "may cause mutations."

The use of short term tests (i.e., in vitro studies) have not been specifically addressed in either the text of the HCS final rule (FR, August 24, 1987) or the preamble discussions. However, it is the Agency's intent under the hazard determination provisions of HCS that the use of in vitro tests do not provide results of significant findings which, in and of themselves, meet the requirements of the rule for a finding of a "significant health hazard". Stated in another way, the results of in vitro tests alone do not represent significant enough information to establish a health hazard for purposes of the hazard communication standard.

It is, of course, the manufacturer's responsibility to review all available scientific data when performing a hazard determination for the chemicals they produce. If the in vitro studies mentioned are the only data available linking a mutagenic response to sodium hypochlorite exposure, these studies do not have to be reported on the product's MSDS.

The hazard communication compliance Instruction, CPL 2-2.38C, mentions the use of in vitro test results briefly in Appendix C, page C-3: "In general, uncorroborated case reports and in vitro studies, such as Ames tests, are useful pieces of information, but not definitive findings of hazards." This also speaks to the Agency's intent that data from in vitro studies alone is not sufficient enough evidence to indicate a health hazard for hazard communication purposes.

The package of information you transmitted to us on this case contained a lengthy discussion of this issue by a Dr. James W. Gillett, Director, Institute for Comparative and Environmental Toxicology of Cornell University. Dr. Gillett discussed the possible mutagenicity of sodium hypochlorite in a letter to Mr. Kramer of the Aquatic Collaboration (the complainant). Dr. Gillett finds that the Ames assay and Chinese hamster cell tests "are typical screening tests with a high degree of false positives and false negatives. Without supporting evidence from the rather extensive human exposure to sodium hypochlorite, the manufacturer probably is not out of line in failing to attach very much validity to the results to date" and that, "the implication is that the Ames test itself is of little value except in guiding further research."

We note Dr. Gillett's discussion that, since the test results of in vitro tests per se are probably irrelevant to any human health hazard, it would instead be extremely worthwhile to improve upon the hazard communication training program for workers who may be exposed to sodium hypochlorite "to emphasize proper handling of NaClO in such a way as to respect all of its potential harmfulness...such strong oxidants and chlorinators have numerous means of damaging genetic material, particularly if the body's defenses are damaged by repeated insult. They are just plain hazardous and should be "handled with extreme caution" and exposure "should be reduced to the lowest possible level, especially when in a concentrated form." This is "just plain good advice," and should be stressed to an employer who is trying to implement an effective hazard communication program for his employees.

We hope this has been responsive to your concerns. For further information, please feel free to contact Melody Sands of my staff at (FTS) 523-8036.