Characterization of occupational exposure to air contaminants in modern tunnelling operations.

OBJECTIVES Personal air measurements of aerosols and gases among tunnel construction workers were performed as part of a 11-day follow-up study on the relationship between exposure to aerosols and gases and cardiovascular and respiratory effects. METHODS Ninety tunnel construction workers employed at 11 available construction sites participated in the exposure study. The workers were divided into seven job groups according to tasks performed. Exposure measurements were carried out on 2 consecutive working days prior to the day of health examination. Summary statistics were computed using maximum likelihood estimation (MLE), and the procedure NLMIXED and LIFEREG in SAS was used to perform MLE for repeated measures data subject to left censoring and for calculation of within- and between-worker variance components. RESULTS The geometric mean (GM) air concentrations for the thoracic mass aerosol sub-fraction, α-quartz, oil mist, organic carbon (OC), and elemental carbon (EC) for all workers were 561, 63, 210, 146, and 35.2 μg m(-3), respectively. Statistical differences of air concentrations between job groups were observed for all contaminants, except for OC, EC, and ammonia (P > 0.05). The shaft drillers, injection workers, and shotcreting operators were exposed to the highest GM levels of thoracic dust (7061, 1087, and 865 μg m(-) (3), respectively). The shaft drillers and the support workers were exposed to the highest GM levels of α-quartz (GM = 844 and 118 μg m(-3), respectively). Overall, the exposure to nitrogen dioxide and ammonia was low (GM = 120 and 251 μg m(-) (3), respectively). CONCLUSIONS Findings from this study show significant differences between job groups with shaft drilling as the highest exposed job to air concentrations for all measured contaminants. Technical interventions in this job should be implemented to reduce exposure levels. Overall, diesel exhaust air concentrations seem to be lower than previously assessed (as EC).