A comparison of respirable crystalline silica concentration measurements using a direct-on-filter Fourier transform infrared (FT-IR) transmission method vs. a traditional laboratory X-ray diffraction method

Abstract

Evaluation and control of respirable crystalline silica (RCS) exposures are critical components of an effective mine industrial hygiene program. To provide more timely exposure data in the field, an end-of-shift Fourier transform infrared (FT-IR) spectrometry method has been developed for evaluation of direct-on-filter RCS. The present study aimed to apply this FT-IR method using field samples collected in three Northwestern U.S. metal/nonmetal mines and compare the results to traditional laboratory X-ray diffraction analysis (XRD). Seventy-five dust samples were analyzed using both methods. Samples for each mine were split in half by random assignment, with half used to create a calibration factor for the FT-IR analysis and half used to apply the calibration. Nonparametric correlational and two-sample comparative tests were used to assess the strength of association and the level of agreement between the two methods. Strong, positive correlations were observed between FT-IR and XRD RCS concentrations, with Spearman rank correlation coefficients ranging between 0.84 and 0.97. The mean RCS concentrations determined through FT-IR analysis were lower than through XRD analysis, with mean differences ranging from −4 to −133 ug/m³ and mean percent errors ranging from 12% to 28%. There was a statistically significant improvement in the level of agreement between log FT-IR and log XRD RCS concentrations following calibration at two of the three mines, with mean differences of −0.03 (p = 0.002) and −0.02 (p = 0.044) in the log scale. The reduction in mean difference following calibration at the other mine was not statistically significant (mean log scale difference = −0.05, p = 0.215), but the differences between FT-IR and XRD were not significantly different without calibration (mean log scale difference = −0.07, p = 0.534). The results indicate that mine-specific calibration factors can improve the level of agreement between RCS concentrations determined via a field-based, end-of-shift FT-IR method in metal/non-metal mines as compared to traditional XRD analysis.

KEYWORDS:

• Direct-on-filter
• Fourier Transform Infrared Transmission (FTIR)
• respirable crystalline silica (RCS)
• X-ray diffraction (XRD)

Acknowledgments

The authors would like to extend a special thank you to our mining industry partners who supported this work by allowing access for air sampling and bulk material collection.

Disclaimer

Mention of any company or product does not constitute an endorsement by the National Institute for Occupational Safety and Health (NIOSH). The findings and conclusions in this paper are those of the authors and do not necessarily represent the views of NIOSH.

Additional information

Funding

Support for this project was provided in part by the Montana Tech NIOSH Training Project Grant (T03 OH008630). The contents of this publication are solely the responsibility of the authors and do not represent the official views of the Centers for Disease Control and Prevention or the National Institute for Occupational Safety and Health. Department of Health and Human Services.