The Crystalline Silica Conundrum
Oral Presentation
Prepared by C. Tuit, A. Lewis, C. Long
Gradient, 20 University Rd, Suite 5000, Cambridge, MA, 02138, United States
Contact Information: ctuit@gradientcorp.com; 617-395-5000
ABSTRACT
Respirable crystalline silica (RCS) has long been a focus of workplace air monitoring due to the risk of silicosis and lung cancer from occupational RCS exposure. Similarly, under GHS regulation, manufacturers must classify products containing crystalline silica for hazards related to carcinogenicity and specific target organ toxicity. Classification can carry significant implications because products labeled as "carcinogenic" are subject to use restrictions from both regulators and downstream users. While there are recommended procedures to measure RCS exposure in size fractionated samples of workplace atmospheres, there is no promulgated method in either the US or the EU for measuring the RCS concentration of a bulk material. Without regulatory guidance, manufacturers must either take the extremely conservative and burdensome approach of classifying on the basis of total crystalline silica (TCS), which is not the relevant biological agent, or use an unsanctioned method to measure RCS concentrations and risk that the results will be rejected by regulators. There are two methods of RCS measurement currently in use: a modified NIOSH 7500 method and the size weighted relative fine fraction method for crystalline silica (SWeRFCS) developed by IMA Europe. The modified NIOSH 7500 method is a conservative estimate of RCS calculated from the TCS concentration of the sample as measured by X-ray Diffraction (XRD) and the Particle Size Distribution (PSD) of the silica-rich particles as measured by computer controlled scanning electron microscopy/energy-dispersive X-ray spectroscopy. The SWeRFCS method includes the option of direct measurement of RCS by sedimentation and XRD analysis or calculation of the RCS fraction from the TCS concentration, the PSD, and the probability function for particle deposition in the lung (EN 418). This presentation will discuss the advantages, disadvantages and regulatory outlook for both methods.
Oral Presentation
Prepared by C. Tuit, A. Lewis, C. Long
Gradient, 20 University Rd, Suite 5000, Cambridge, MA, 02138, United States
Contact Information: ctuit@gradientcorp.com; 617-395-5000
ABSTRACT
Respirable crystalline silica (RCS) has long been a focus of workplace air monitoring due to the risk of silicosis and lung cancer from occupational RCS exposure. Similarly, under GHS regulation, manufacturers must classify products containing crystalline silica for hazards related to carcinogenicity and specific target organ toxicity. Classification can carry significant implications because products labeled as "carcinogenic" are subject to use restrictions from both regulators and downstream users. While there are recommended procedures to measure RCS exposure in size fractionated samples of workplace atmospheres, there is no promulgated method in either the US or the EU for measuring the RCS concentration of a bulk material. Without regulatory guidance, manufacturers must either take the extremely conservative and burdensome approach of classifying on the basis of total crystalline silica (TCS), which is not the relevant biological agent, or use an unsanctioned method to measure RCS concentrations and risk that the results will be rejected by regulators. There are two methods of RCS measurement currently in use: a modified NIOSH 7500 method and the size weighted relative fine fraction method for crystalline silica (SWeRFCS) developed by IMA Europe. The modified NIOSH 7500 method is a conservative estimate of RCS calculated from the TCS concentration of the sample as measured by X-ray Diffraction (XRD) and the Particle Size Distribution (PSD) of the silica-rich particles as measured by computer controlled scanning electron microscopy/energy-dispersive X-ray spectroscopy. The SWeRFCS method includes the option of direct measurement of RCS by sedimentation and XRD analysis or calculation of the RCS fraction from the TCS concentration, the PSD, and the probability function for particle deposition in the lung (EN 418). This presentation will discuss the advantages, disadvantages and regulatory outlook for both methods.
