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OSHA Hazard Communication Letters of Interpretation
Hazard communication requirements for diatomaceous earth.
- Issued
- Record type
- Interpretation
- Historical standard
- HCS 1994, pre-GHS archive
- Current standard
- HCS 2024, as amended
ILPI assessment: Historical enforcement policy; current classification criteria must be applied
This letter addresses the obsolete 1994 version of the Hazard Communication Standard (HCS). The memorandum concerns natural, uncalcined diatomaceous earth. Its old single-positive-study test and discussion of a 1% crystalline-silica boundary must not be used as current classification shortcuts. IARC Group 3 means not classifiable, not demonstrated noncarcinogenic.
Under the current HCS, use hazard classification and the carcinogenicity criteria, including the applicable mixture thresholds and SDS disclosure requirements. OSHA's 2012 follow-up distinguishes calcined from natural material; calcined products are not cleared by this memo. Exposure control for respirable crystalline silica is a separate obligation under 1910.1053 where applicable.
Last reviewed: .
About this ILPI assessment
This comparison with current requirements is not a finding that OSHA has formally withdrawn this letter. This assessment reflects editorial judgment informed by human review and AI assistance. It is an opinion, may contain errors or omissions, and is not an official OSHA determination. For guidance on how OSHA requirements apply to your circumstances, contact your local OSHA office.
OSHA's notice about interpretation letters
The following notice is published on OSHA's interpretation pages; it is general guidance, not a letter-specific withdrawal notice.
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.
Source: OSHA's original letter page.
April 5, 1999
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MEMORANDUM TO: REGIONAL ADMINISTRATORS
FROM: RICHARD E. FAIRFAX. DIRECTOR, DIRECTORATE OF COMPLIANCE PROGRAMS
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 [ILPI: Original HCS 1994 context · Current HCS], 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.
[ILPI note: At issuance: HCS 1994, pre-GHS archive. The old single-positive-study approach was replaced by hazard-specific classification criteria. Evaluate all relevant evidence and the actual product; this memo does not establish a general current 1% exemption.]
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.
The original official public domain version of this document is available from OSHA at https://www.osha.gov/laws-regs/standardinterpretations/1999-04-05.