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 http://www.osha.gov.

April 5, 1999



Subject:          Clarification on Enforcement Policy under the Hazard 
                  Communication Standard for Diatomaceous Earth

This memorandum is to provide clarification regarding enforcement policy under the Hazard Communication Standard (HCS), 29 CFR 1910.1200, for uncalcined diatomaceous earth products. Questions have been raised regarding the information which must be included on MSDSs and labels for these products. Specifically, we have been asked to clarify the information required for the health effects of silicosis and carcinogenicity. (Diatomaceous earth is defined as amorphous silica composed of the skeletons of prehistoric plants, or diatoms, containing less than one percent crystalline silica.)

Studies of the fibrogenic potential (silicosis) of diatomaceous earth provide conflicting evidence - some showing positive results and some showing negative. Since the criterion for establishing and reporting health hazards under the HCS is "evidence which is statistically significant and which is based on at least one positive study conducted in accordance with established scientific principles," information on the adverse health effects resulting from exposure must be reported on the label, and a discussion of the potential for silicosis must be included on the MSDS.

Regarding carcinogenicity, the HCS requires any chemical which has been designated a carcinogen (or potential carcinogen) by the International Agency for Research on Cancer (IARC), the National Toxicology Program (NTP), or is regulated as a carcinogen by OSHA to be listed as a carcinogen on the MSDS.

Diatomaceous earth has been tested as a whole and evaluated as a Group 3 carcinogen by IARC. A Group 3 listing indicates that diatomaceous earth is not classifiable as to its carcinogenicity to humans, since definitive conclusions cannot be drawn from the research conducted to date. Therefore, there is no requirement under the HCS to state a definitive finding of carcinogenicity on the label or MSDS for diatomaceous earth products containing less that 1% crystalline silica. However, the principle of "one positive study" applies here as well, and the results of any study conducted in accordance with scientific principles which shows statistical significance of carcinogenicity resulting from exposures to this product must be included for discussion on the MSDS. This enforcement policy does not apply to products containing greater than 1% crystalline silica, and cancels and supersedes all prior interpretations on this issue.

We hope this information is helpful. Should you need any further assistance in this regard, please do not hesitate to contact the Office of Health Compliance Assistance on 202-693-2190.