Determinants of respirable crystalline silica exposure in Australian tunnelling

Exposure to respirable crystalline silica (RCS) is a well-established cause of silicosis, lung cancer, and other serious health conditions. Contemporary data describing RCS exposures among tunnel construction workers in Australia has been limited, restricting an understanding of the nature and magnitude of the risk of exposure. This observational study addresses that gap by accessing, compiling, and evaluating the largest known dataset of RCS exposures in contemporary Australian tunnelling. Data were obtained through freedom of information requests and parliamentary records, resulting in 3,288 individual personal exposure measurements across 12 tunnel projects constructed between 2016 and 2024, employing a range of construction methods: via tunnel boring machines, drill and blast, cut-and-cover, and mined tunnelling. Determinants of exposure were assessed on ln-transformed data using linear mixed models (LMM), and included primary location, proportion of crystalline silica content in respirable dust, tunnelling method, or specific above-ground work location. LMMs explained between 53% and 68% of the observed variability in RCS exposures. Underground workers were predicted to have 2.3 times the RCS exposures of above-ground workers (geometric mean [GM] 0.026 vs 0.012 mg/m3); and each 1% increase in the proportion of RCS in respirable dust corresponded to a predicted 5% increase in RCS exposure. Estimated RCS exposure was lower after the reduction of the workplace exposure standard in July 2020 (GM 0.023 vs 0.013 mg/m3). Above-ground exposure varied by location (eg precast facilities, spoil sheds, or general site areas), while tunnelling method influenced RCS exposure underground (eg mined tunnelling, using tunnel boring machines or cut-and-cover methods). While limitations such as variable data quality and incomplete task attribution are acknowledged, the findings support the need for targeted control measures and transparent access to data across tunnel construction environments.