Exposure level and distribution of airborne bacteria and fungi in an urban utility tunnel: A case study

Abstract

Occupational health in underground workplaces, especially underground utility tunnels in China, is a hot issue. In this study, environmental measurements were conducted in an urban utility tunnel in Nanjing, China. The exposure level and size distribution of airborne bacteria and fungi were measured in three typical sections. The airborne bacteria and fungi average concentrations ranged from 202 to 516 CFU/m3 and 729 to 931 CFU/m3, respectively, which conform to the criteria of the Indoor air quality standard of China (<2500 CFU/m3) and the recommended values of the Commission of the European Communities (>1000 CFU/m3) and National Institute of Occupational, Safety and Health (not exceeding 1000 CFU/m3). Compared to other underground built environments, the bacterial concentration in the utility tunnel was similar to that of underground stations with few passengers, although the fungal concentration was 3.2 times higher than that of underground stations. Analyses of DNA extracted from airborne fungi showed relative Aspergillus and Cladosporium abundances of over 5% at all tested points. The size distribution showed that most of the airborne bacteria had aerodynamic diameters larger than 7.0 μm, while most airborne fungi had diameters between 1.1 and 3.2 μm. A ventilation evaluation showed that it is effective for removing airborne bacteria and fungi.