Underground » Health and Safety
Monitoring of personal exposure levels of respirable coal dust (RCD) and respirable crystalline silica (RCS) is an important step in protecting mine workers from dust related occupational respiratory lung diseases. Timely monitoring and reporting of personal exposure levels is crucial for dust control and exposure management.
Thermo Scientific Personal Dust Monitor (PDM) is a real‐time mass‐based respirable dust monitor designed specifically for coal mining applications in USA. The PDM utilises a Tapered Element Oscillating Microbalance (TEOM) technology that continuously weighs a filter as the respirable dust is deposited on it, thus monitoring in real time personal exposure levels of RCD and hence aiding the miners in reducing their exposure to coal mine dust. PDM has been also deployed in Australian coal mines since 2016.
The PDM does not provide information specific to silica exposure. The current practice for measuring the exposure to silica is to submit the filter sample collected by the traditional gravimetric sampler to a laboratory where the mass of quartz in the filter sample is measured by Fourier transform infrared (FTIR, NIOSH 7603) and X‐ray diffraction (XRD, NIOSH 7500) analytical procedures. The filter material for sampling in the above FTIR and XRD methods is generally polyvinyl chloride which is readily ashed by incineration or dissolved by organic solvent to redeposit collected dust particles for subsequent silica analysis. As PDM uses a glass fibre filter for mine dust sampling, the FTIR and XRD analytical methods cannot be directly applied to silica analysis for coal mind dust samples collected by the PDM3700 due to analytical measurement interference.
This project aimed to develop a redeposition methodology to enable the silica content determination of respirable coal mine dust collected over the PDM glass fibre filter using FTIR analytic method, to advance the TEOM based PDM technology by achieving both real-time RCD monitoring throughout the shift and RCS measurement at the end of the shift by using a single PDM3700. It is envisaged that these would significantly improve RCD and RCS personal exposure monitoring capabilities to identify potential high personal exposure areas and tasks for effective engineering controls.
In this work, parallel dust sampling using PDM3700 and traditional gravimetric personal dust samplers was carried out with a laboratory dust test chamber to obtain dust samples with various total dust mass (0.4-1.7 mg) and silica concentrations (0.9-4.5 wt%). The collected dust sample was effectively detached from the PDM filter into a solvent using a CSIRO invented backflush method, followed by a filtration process to redeposit the dust particles onto a PVC membrane filter. The newly developed backflush method has been demonstrated to be effective in detaching dust particles from the PDM glass fibre filter without causing sample contamination by glass fibres as examined using detailed optical microscope and scanning electronic microscopy (SEM) analysis. The redeposited dust sample on the PVC membrane was measured for silica content with FTIR by using an on-filter method without ashing the filter sample. Such an on-filter FTIR analysis method is preferred for field applications at the mine site, due to its simple process and no requirement for complex laboratory sample preparation for polymer filter destruction.
The developed methodology, described in the report, is a simple and rapid process with very simple setup and ease of operation. The setup is readily installed at a mine site, and the entire process for dust detachment, redeposition and FTIR analysis takes about 15-20 min.
Phase 2 of this project, being the optimisation and field demonstration of the developed methodology, is ongoing with outcomes expected mid 2026.