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An Even Closer Look at Portland Cement
Editor’s note: In response to feedback from the Portland Cement Association, notes have been added to the digital version of “A Close Look at Portland Cement” to clarify that, after fabrication, most of the silica in portland cement may be amorphous silica, not crystalline.

The Synergist
published “A Close Look at Portland Cement: Respirable Crystalline Silica and Other Hazards of a Familiar Substance" by Veronica Stanley (
February issue
). The Portland Cement Association’s Occupational Health and Safety Committee, including Certified Industrial Hygienists, reviewed the article with concern. 

The article contains factual inaccuracies and misleading claims, and reflects an incomplete understanding of portland cement’s physical composition, its widespread and safe use in commerce, and the extensive measures taken by cement manufacturers and downstream users to minimize hazards in the workplace.  Most notably, the article states that “after fabrication, portland cement may have about 25 percent silica-containing material.” This attempt to link the term “silica-containing material” to the presence of crystalline silica is misleading. Portland cement production chemically transforms any silica-containing materials at temperatures in excess of 1450°C to calcium
—a separate class of compounds with completely different physical, chemical, and hazard characteristics. Indeed, as acknowledged later in the article, NIOSH defines portland cement as containing less than 1 percent crystalline silica, contradicting the article’s assertion. ASTM standards, in turn, limit the presence of insoluble residues, including crystalline silica, to no more than 1.5 percent. In practice, typical levels of crystalline silica fall below 0.2 percent.  The article correctly identifies that OSHA specifically excluded portland cement from the hexavalent chromium standard, determining that whatever traces of this metal might be found in some portland cement, workers would not be exposed to levels approaching the final rule’s permissible exposure limit. The article failed to note, however, that the rule’s preamble also addressed concerns with dermal exposure to portland cement by workers who might be allergic to hexavalent chromium, finding that the personal protective equipment already recommended for those working with wet cement and wet concrete would also protect those allergic to hexavalent chromium.  In a similar vein, the article suggests the presence of “other heavy metals of concern” and that concentrations of such metals vary geographically and with adjustments “to produce colors.” While it is true that any mineral mined from the ground may have varying compositions by area or region, it is incorrect to create the inference that portland cement contains these metals at harmful levels. Also, adjustments are not made during the cement manufacturing process to produce colors; portland cement as manufactured is either naturally gray or white in color. In addition, the article notes that “at least 22 different solid phases of portland cement have been identified, some of which are not stable.” While the existence of 22 different solid phases may be true, the “stability” of those phases is totally unrelated to health and safety issues, and any suggestion to the contrary is misleading at best. We appreciate the ability to respond to this article and to address some of our concerns. The cement industry is deeply committed to ensuring both workplace and product safety and is working collectively to monitor and address potential hazards associated with its products and to develop and maintain robust data supporting its efforts. PCA and its member companies are prepared to help OEHS professionals, researchers, and the public have an accurate understanding of our materials, products, and hazards.
Stephen J. Robuck Sr. Director, Government Affairs Portland Cement Association

The industrial hygiene community and product manufacturers have a mutual interest in collaborating to address gaps in knowledge and develop consensus around terminology and definitions. 
Stanley responds:
I thank Stephen Robuck for continuing this important discussion. I understand his concerns about the implications of my article but disagree with his claims that it is misleading and contains factual inaccuracies.  The Portland Cement Association’s website states that the organization “represent(s) 92 percent of U.S. cement production capacity.” PCA is an important stakeholder in the necessary conversation for addressing the issues discussed in my article. I encourage PCA, the “premier policy, research, education, and market intelligence organization serving America’s cement manufacturers,” to share data, reducing the information gap at issue.  My article was written from the standpoint of industrial hygienists who must assess workplace hazards and determine compliance using available information. It represents an industrial hygienist’s perspective, not a manufacturer’s perspective. Used worldwide, portland cement is manufactured under varied standards of which I have not claimed to be an expert. Portland cement has a long history of use—to my knowledge, cementing materials were in use as far back as the Roman Empire.  Therefore, the definition of PC used within the article matters. The article pointed out that OSHA’s definition of PC is generic; it therefore does not match the definition found in PC manufacturing standards, such as ASTM C150, “Standard Specification for Portland Cement.” The details of various PC manufacturing standards and associated compositions were not the focus of the article. I mentioned that there are multiple manufacturing standards to make the point that PC is not one uniform product.  It is important to note that ASTM C150 is a manufacturing standard, specifying performance characteristics (for example, setting time, potential expansion, early stiffening, and so on). Data from performance characteristics sampling provides useful information, but, to my knowledge, these values cannot be directly used in place of data obtained through accepted sampling methods for determining regulatory compliance with exposure limits. Perhaps those correlations can be explored. At present, “insoluble residues” do not seem to apply to the regulatory issues that concern industrial hygienists. If PCA has further information about the implications of “insoluble residues” or a definition for the term, I encourage the organization to share this information. In particular, industrial hygienists would find valuable any scientific research studies that address the relationship between “insoluble residues” and crystalline silica (quartz) and the risk of exposure to “insoluble residues” in portland cement. Also of interest to the industrial hygiene community would be studies or technical reports that include any test results specific to crystalline silica (quartz) obtained from bulk samples of portland cement. Regarding the statement in the article that PC comprises 25 percent silica-containing material, I was not claiming that all of the silica was crystalline. The 25 percent value is based on
references from OSHA
and is supported by PCA’s own publication, “Chemical and Physical Characteristics of US Hydraulic Cements: 2014” (
).  As stated in my article, industrial hygienists are interested in respirable crystalline silica (crystalline SiO2) that has become, or has the potential to become, small enough in size to be respirable. There appears to be disagreement about how much of the 25 percent SiO2 in portland cement is crystalline. I have not assumed values when quoting OSHA and NIOSH. I also did not assume or imply a connection to health and safety hazards to workers from the 22 mentioned phases of PC. Such information can be relevant to industrial hygienists as we are interested in assessing exposures and determining the risk of exposures.  The information about hexavalent chromium and other metals was taken from OSHA, NIOSH, the National Center for Biotechnology Information, PubMed, and other sources respected by our profession. OSHA publishes “
Preventing Skin Problems from Working with Portland Cement
.” My article mentioned the specific metals found within PC because industrial hygienists tasked with assessing exposures should familiarize themselves with the overall compositions of the material being sampled. I appreciate the valuable recommendations provided by manufacturers. My suggestion in the article that industrial hygienists review the information provided by manufacturers and by those using the product was an endorsement of value. The industrial hygiene community and product manufacturers have a mutual interest in collaborating to address gaps in knowledge and develop consensus around terminology and definitions. I ask that PCA please consider sharing any robust data it has developed and maintained with AIHA.
Veronica Stanley, MSPH, CIH, CSP, CESCP