Objectives Chronic obstructive pulmonary disease and silicosis are associated with exposure to crystalline silica. We determined the exposure to respirable crystalline silica and estimated exposure–response relationships between cumulative exposure and pulmonary function in outdoor rock drillers.
Methods 136 rock drillers and 48 referents were recruited from three heavy construction companies. 98 air samples were collected by personal sampling for determination of respirable particulate matter and crystalline silica. Information about individual job tasks, type of drilling equipment and years of exposure in different job categories was obtained by interview. Cumulative exposure to crystalline silica was calculated for all workers. Pulmonary function was assessed by spirometry. A subgroup of 39 subjects with high cumulative exposure to crystalline silica underwent high-resolution computed tomography (HRCT).
Results Cumulative exposure (mean (min–max)) to crystalline silica was 0.69 mg٠years m–3 (0.01–5.89) in the exposed group. Mean time of exposure among rock drillers was 10.7 years (1–42). Compared with referents, the rock drillers had a lower forced expiratory volume in one second/forced vital capacity ratio (79.4 vs 81.4, p<0.05) and maximal mid-expiratory flow% (85.6 vs 93.9, p<0.05). Further, by stratifying the exposed workers into three equally large groups, a dose–response relationship was demonstrated in the highest exposed group, also in never smokers, at a mean cumulative exposure of 21.7 years at 0.08 mg٠m–3/years. Silicosis was not detected in HRCT, but other patterns of fibrosis and emphysema were seen.
Conclusions Outdoor rock drillers exposed to crystalline silica had significantly lower pulmonary function than referents, and signs of airflow obstruction. Silicosis was not detected.
- hygiene / occupational hygiene
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Contributors BU, NPS, MBL and DGE designed the study. MU, TC, BU and NPS were responsible for data collection. AG and TMA reviewed the HRCT. BU and DGE were responsible for statistical analyses and drafting the manuscript. The manuscript was critically reviewed and approved by all authors.
Funding The study was carried out with financial support from The Fund for Regional Safety Representatives for Building and Construction Activities (Norway).
Competing interests None declared.
Patient consent for publication Informed written consent
Ethics approval This study was approved by South East Norwegian Regional Ethical Committee for Medical Research (REK) (2015/2116).
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available upon reasonable request. Data are available in a secure database.