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...