Quantification of Respirable Dust Concentration at an Underground Copper Mine Using a Personal Optical Particle Counter

Exposure assessments are conducted using standardized
gravimetric
sampling (SGS) methodologies. However, the gravimetric analysis of
respirable dust (RD) provides only one data point. Based on this background,
this study aims to quantify RD concentration and peak RD exposure
detected as time-series data using a personal optical particle counter
(OPC) for possible applications of exposure monitoring in near-real
time. Thirty pairs of side-by-side RD exposure samples were collected
(22 personal and 8 static) using the Nanozen DustCount 9000Z1 OPC
and SGS (NIOSH 0600). The SGS samples were sent for gravimetric analysis
in an ISO 17025:2005-accredited analytical laboratory. A correction
equation for the OPC sensor was established using linear regression
and was used to correct the RD concentrations that were quantified
by the OPC. The RD concentrations quantified by the OPC sensor were
strongly correlated with those of the SGS method (r = 0.93), and the Bland-Altman analysis showed a consistent pattern
and that, on average, the SGS method measured 0.27 mg/m3 higher than the OPC sensor. The time-weighted average RDopc concentrations were less than 1.5 mg/m3 for the mine
sections sampled; the highest peak RDopc concentration
was 11.51 mg/m3. The results from the side-by-side sampling
showed a consistently positive bias, and the Pearson correlation was
strong. Thus, the results from Nanozen DustCount 9000Z1 could be corrected
using the SGS results and linear regression. The corrected RD concentration
can be used to assess the efficacy of the engineering controls in-time.
The exposure data from the OPC complement the SGS results by providing
additional exposure data such as peak exposure and particle size distribution.
From the corrected RD exposure data, the RCS was estimated. Based
on the results of this estimate, there is potential for overexposure
to RCS at this mine; thus, miners are likely to develop silicosis.