Performance Comparison of Four Portable FTIR Instruments for Direct-on-Filter Measurement of Respirable Crystalline Silica

Abstract

Exposure to dusts containing respirable crystalline silica is a recognized hazard affecting various occupational groups such as miners. Inhalation of respirable crystalline silica can lead to silicosis, which is a potentially fatal lung disease. Currently, miners’ exposure to respirable crystalline silica is assessed by collecting filter samples that are sent for laboratory analysis. A more timely field-based silica monitoring method using direct-on-filter (DoF) analysis is being developed by researchers at the National Institute for Occupational Safety and Health (NIOSH) to provide mine operators with the option to evaluate miners’ exposure at the mine. This field-based silica monitoring technique involves the use of portable Fourier transform infrared (FTIR) instruments. As a step in the development of this new analytical technique, four commercially available portable FTIR instruments were evaluated for their ability to provide reproducible measurements from filter samples containing respirable crystalline silica. Reported testing indicates that measurements varied within ±4.1% between instruments for filter samples that contained high-purity respirable crystalline silica. Measurements varied within ±3.0% between instruments for filter samples that contained varying mineral composition. Filter samples were repeatedly analyzed by the same instrument over short and extended periods of time, and mean coefficients of variation did not exceed ±1.6 and ±2.4%, respectively. Mixed model analysis revealed that there was no statistically significant (P < 0.05) change in average measurements made over an extended period of time for all instruments. Results suggest that each of the four FTIR instruments evaluated in this study were able to generate precise and reproducible DoF analysis results of respirable dust samples.

Review of Respirable Coal Mine Dust Characterization for Mass Concentration, Size Distribution and Chemical Composition

“…NIOSH developed a direct-on-filter silica quantification method using portable FTIRs that can provide end-of-shift measurements on site [294,295]. However, interferences from other minerals can lead to inaccurate silica quantification [296,297]. Spectrum deconvolution and correction algorithms are still under development.…”

Direct-on-filter analysis for respirable crystalline silica using a portable FTIR instrument.

“…At the focal point, the infrared beam in the four portable FTIR instruments evaluated by NIOSH is fixed and ranges from 6 to 9 mm [Ashley et al 2020], each of which is larger than the inlet openings commonly found in the traditional three-piece sampling cassette. The material of the cassette absorbs much of the IR beam, leaving insufficient signal for an accurate analysis.…”

“…This document contains guidance applicable to portable Fourier transform infrared spectroscopy (FTIR) instruments in general, though some instrument-specific guidance is also provided where necessary. While researchers from the National Institute for Occupational Safety and Health (NIOSH) have conducted extensive investigation on the use of four portable Fourier transform infrared spectroscopy (FTIR) instruments [Ashley et al 2020], other models of FTIR instruments may also be available and compatible with field-based monitoring.…”

Best practices for dust control in coal mining, second edition.

“…It should be noted that this method is not intended to be used for compliance determination. Four commercially available FTIR instruments (Figure 2.6) were used in initial NIOSH testing, with all units performing satisfactorily [Ashley et al 2020].…”