August 24, 2012

Mr. Patrick T. Flynn, Jr.
Industrial Minerals Consultant
4155 Jasper Lane
Reno, Nevada 89509

Dear Mr. Flynn:

Thank you for your letter to the Occupational Safety and Health Administration's (OSHA) Directorate of Enforcement Programs. You requested clarification of OSHA's enforcement policy for classifying calcined diatomaceous earth (DE) as a carcinogen under the Hazard Communication Standard (HCS), 29 CFR 1910.1200. We apologize for the delay in responding to your question. Since receiving your letter there has been a major revision to the HCS, which OSHA published in the Federal Register in March 2012. This letter constitutes OSHA's interpretation only of the requirements herein, and may not be applicable to any situation not delineated within your original correspondence. Your paraphrased question and our reply are below.

Background: You previously submitted a letter to OSHA on September 13, 2000, concerning calcined DE, on behalf of your previous employer, and we replied with a letter of interpretation dated February 20, 2001. (See attached copy of our 2001 letter.) That discussion referred to the carcinogenic Group 3 classification ¹ for amorphous silica, including natural, uncalcined DE, as determined in 1997 by the International Agency for Research on Cancer (IARC) ² , as well as a subsequent OSHA memorandum, Clarification on Enforcement Policy under the Hazard Communication Standard for Diatomaceous Earth, April 5, 1999.

In your follow-up letter to OSHA on July 6, 2004, you pointed out that the IARC monograph acknowledged that naturally occurring DE may contain up to four percent crystalline silica, mainly quartz and trace amounts of cristobalite. You suggested that the trace cristobalite is likely formed by a volcanic heating process, in a similar manner that cristobalite is formed in the calcining during manufacturing. You then repeated your opinion that lightly calcined DE, such as produced by your client, and containing less than one percent crystalline silica (quartz and cristobalite), should be considered toxicologically equivalent to natural, uncalcined DE, and therefore be classified as IARC Group 3. You thus believe that a lightly calcined product with a total crystalline silica content below one percent should be considered a tested mixture under the HCS, and not requiring the MSDS to indicate carcinogenicity of the trace amount of crystalline silica. ³

Question: Would OSHA revise its past determination, to consider all DE products [both natural and lightly calcined] that contain less than one percent crystalline silica as equivalent (IARC Group 3)?

Response: OSHA's past determination, as stated in its 1999 memorandum, was that, "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." The one percent (1%) cutoff for crystalline silica only applies to natural, uncalcined DE, as evaluated by IARC. The basis for specifying the 1% cutoff was because this is the method detection limit for OSHA's analytical method, x-ray diffraction, used to measure crystalline silica.

OSHA also clarified in our 2001 letter that, "OSHA makes a distinction between uncalcined and calcined diatomaceous earth products containing less than one percent crystalline silica. The specific product you are concerned with, calcined diatomaceous earth containing less than one percent crystalline silica, has not been evaluated as a whole by IARC and is not part of the IARC Group 3 classification."

In response to your inquiry of 2004, OSHA's Office of Occupational Medicine recently conducted a review of current scientific literature, and found no new evidence that showed natural and calcined forms of DE are toxicologically equivalent. While you've pointed out that IARC acknowledged that natural DE may contain 0.1 to 4% of crystalline silica, we respond that most of this silica is in the form of quartz.⁴ You are aware that the calcination process converts some of the amorphous silica and/or quartz in the natural DE into cristobalite. ⁵

In conclusion, OSHA finds that there is insufficient information to support your assertion that calcined DE with less than one percent crystalline silica is toxicologically equivalent to natural, uncalcined DE. The calcination process alters the original composition of the natural, uncalcined DE by creating a material with a higher percentage of cristobalite, a known IARC Group 1 carcinogen. Thus, even though the total crystalline silica content remains less than one percent, OSHA considers the calcined material dissimilar to the original natural DE. Unless the calcined material is tested as a whole, the material would need to follow the requirements specified in the HCS for untested mixtures.

You should also be aware that on March 26, 2012, a revised HCS was published in the Federal Register. Some of the changes in the revised HCS include a standardized classification system for chemicals, replacing MSDSs with Safety Data Sheets (SDSs), and required information on product labels. ⁶ For classifying the hazards of chemical mixtures, the revised HCS requires that, "Chemical manufacturers, importers, or employers evaluating chemicals shall follow the procedures described in Appendices A and B to §1910.1200 to classify the hazards of the chemicals, including determinations regarding when mixtures of the classified chemicals are covered by this section." [29 CFR 1910.1200(d)(3)(i)]

You may be interested to know that under the revised HCS, manufacturers can perform their own hazard classification for carcinogenicity based on the weight of evidence, which is a change from the previous version of the HCS that required manufacturers to classify any chemical or mixture of chemicals that contains more than 0.1% of a chemical listed as a carcinogen by either IARC, the National Toxicology Program (NTP), or OSHA. The revised HCS, Appendix A, Health Hazard Criteria (mandatory), Section A.6, Carcinogenicity, provides the specific procedures for the classification of chemicals and mixtures regarding their carcinogenicity. These include the use of cut-off values/concentration limits, available test data for the mixture as a whole, then the use of bridging principles. See Appendix A of the revised HCS for additional information, as well as Appendix F, Guidance for Hazard Classifications re: Carcinogenicity (non-mandatory).

Thank you for your interest in occupational safety and health. We hope you find this information helpful. 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 continue to consult OSHA's website at www.osha.gov. If you have any further questions, please feel free to contact our Office of Health Enforcement at 202-693-2190.

Sincerely,

Thomas Galassi, Director
Directorate of Enforcement Programs

Attachment: OSHA Letter to Mr. Patrick Flynn, February 20, 2001

1 A Group 3 listing by IARC indicates that a substance is not classifiable as to its carcinogenicity to humans, since definitive conclusions cannot be drawn from the research conducted to date.

2 IARC Monographs on the Evaluation of Carcinogenic Risks to Humans; Volume 68, Silica, Some Silicates, Coal Dust and para-Aramid Fibrils, 1997, pp. 168-174.

3 The specific HSC requirement is at paragraph 29 CFR 1910.1200(g)(2)(i)(B) (2011), "If the hazardous chemical is a mixture which has been tested as a whole to determine its hazards, the chemical and common name(s) of the ingredients which contribute to these known hazards, and the common name(s) of the mixture itself [must be listed on the product's material safety data sheet or MSDS]."

4 IARC Monographs on the Evaluation of Carcinogenic Risks to Humans; Volume 68, Silica, Some Silicates, Coal Dust and para-Aramid Fibrils, 1997, p. 50.

5 Ibid, pp. 80-81.

6 OSHA has created a webpage for the revised HCS, which includes the text of the Federal Register notice, in addition to comparison documents, a list of the effective dates, and outreach material. This information can be found at www.osha.gov/dsg/hazcom/index.html. Please note, during the implementation period both standards are applicable, and manufacturers, importers, distributors, and employers may comply with either version or both.

Attachment

February 20, 2001

Mr. Patrick T. Flynn
Eagle-Picher Minerals, Inc.
6110 Plumas Street
Reno, NV 89509

Dear Mr. Flynn:

Thank you for your September 13 letter to the Occupational Safety and Health Administration's (OSHA's) Directorate of Compliance Programs. We earlier responded to your inquiry with an interim letter. Please consider this a final letter and be aware that it constitutes OSHA's interpretations only of the requirements discussed and may not be applicable to any question not delineated within your original correspondence. Your requests are paraphrased and the replies provided are further explained below.

Request: Would OSHA clarify the Hazard Communication Standard's (HCS's) 29 CFR 1910.1200 labeling requirements for Diatomaceous Earth products considered to be "calcined" but which have crystalline silica contents at the same levels as natural, uncalcined products (that is, less than 1% crystalline silica)?

Reply: OSHA makes a distinction between uncalcined and calcined diatomaceous earth products containing less than one percent crystalline silica. The specific product you are concerned with, calcined diatomaceous earth containing less than one percent crystalline silica, has not been evaluated as a whole by IARC and is not part of the IARC Group 3 classification. The crystalline silica contained in calcined diatomaceous earth (primarily cristobalite), however, has been classified as Group 1, carcinogenic to humans.

Request: Would OSHA eliminate the requirement under the HCS for labeling as a carcinogen diatomaceous earth products (natural or calcined) containing less than one percent crystalline silica?

Reply: Calcined diatomaceous earth products containing less than one percent crystalline silica have not been evaluated as a whole by IARC; therefore, OSHA cannot support the Group 3 classification as you propose. These products must be labeled and identified on the MSDS as a carcinogen because of the greater than 0.1 % crystalline silica content. Regarding natural diatomaceous earth products containing less than one percent crystalline silica, the Group 3 classification means that there is no requirement to make a definitive statement of carcinogenicity on the label or MSDS, although the results of individual positive studies such as the one by Bryson and Bischoff (1967)¹ must be reported on the MSDS.

To our knowledge, there are few to no toxicological studies which have been conducted on calcined DE products containing less than one percent crystalline silica. For this reason, OSHA does not agree that there would be no toxicological difference between calcined or uncalcined diatomaceous earth products containing less than one percent crystalline silica. OSHA has not been provided with sufficient information regarding the calcining process, the number of replicate samples taken in Eagle-Picher's determination, the consistency of these results, or the toxicological endpoint of exposure to this product. Additionally, the crystalline silica in your product contains less than one percent crystobalite as opposed to quartz, which would be the form of crystalline silica in the natural, uncalcined product. As there is a significant difference between the toxicology of these two substances, and as this product has not been tested as a whole to determine its carcinogenicity, the requirement under the Hazard Communication Standard for this product is to identify it as a carcinogen on the label and MSDS.

As you know, a Group 3 classification is an inconclusive finding. That is to say, the carcinogenicity of the product could not be determined based upon the body of knowledge for that chemical at the time of the evaluation. With regards to uncalcined DE, IARC acknowledged the study by Bryson and Bischoff (1967)¹ which demonstrated the induction of lymphoma in experimental animals, but noted the presence of crystalline silica in the DE. IARC appears to have been very concerned that the crystalline silica confounded the positive findings with regard to DE only. While the standard allows the exclusion of definitive statements on the label and MSDS for Group 3 carcinogens, many of these chemicals report conflicting studies, the results of which should be held in regard by the scientific community with concern to their carcinogenic potential.

When this is the situation, the HCS employs the principle of "one positive study." That is to say, even though a chemical is not required to be labeled with a definitive finding of carcinogenicity, the results of any study conducted in accordance with scientific principles which shows statistical significance of a health hazard, must be discussed on the MSDS. This means that the results of any individual study which indicates carcinogenicity for uncalcined DE products containing less than 1% crystalline silica, has to be reported on the MSDS.

It is understandable that these differing "levels" of data have caused confusion. We want to clarify that while the principle of one positive study applies for all chemicals, the HCS has adopted a specific framework with regard to carcinogenicity. The HCS identifies IARC (Group 1 or 2A), NTP and OSHA as sources which establish a definitive finding. A positive finding by one of the above-mentioned sources is conclusive, supercedes individual studies, and must be positively noted on the label and MSDS.

Further information and guidance is provided in our compliance directive, "Inspection Procedures for the Hazard Communication Standard," CPL 2-2.38D, which can be found on our internet site (www.osha.gov). Table 1 from this directive is enclosed for your convenience and information.

Thank you for your interest in occupational safety and health. We hope you find this information helpful. OSHA requirements are set by statute, standards, 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 interpretations 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. If you have any further questions, please feel free to contact the Office of Health Compliance Assistance at 202-693-2190.

Sincerely,

Richard E. Fairfax, Director
Directorate of Compliance Programs

1 Bryson, G. and Bischoff, F. (1967) Silicate-induced neoplasms. Prog. Exp. Tumor Res., 9:77-164.