Enclosed underground excavation worksite has an environment with poor ventilation and exposure to hazardous substances from diesel engine exhaust and construction materials. The objective of this study was to evaluate the exposure level of elemental carbon (EC), organic carbon (OC), total carbon (TC), polycyclic aromatic hydrocarbons (PAHs), dust and crystalline silica (CS) during underground excavation work for top down construction buildings. Active local air sampling for EC, OC, and TC (n = 105), PAHs (n = 50), dust (n = 34) and CS (n = 34) was conducted from inside and outside the excavator at underground excavation workshop in four different construction sites. EC, OC, TC and CS were sampled with each respirable and total particulates. EC, OC, and TC were collected on quartz-filter and analyzed using the thermal optical transmittance method. PAHs was collected on polytetrafluorethylene filter with XAD-2 and analyzed using liquid chromatography with fluorescence detector. CS and particulates were collected on poly vinyl chloride filter and analyzed using fourier-transform infrared spectroscopy. The geometric mean of respirable EC, OC, TC, total PAHs, respirable dust and respirable CS were 8.69 μg/m 3 , 34.32 μg/m 3 , 44.96 μg/m 3 , 6.818 μg/m 3 0.13 mg/m 3 and 0.02 mg/m 3 from inside the excavator and 33.20 μg/m 3 , 46.53 μg/m 3 , 78.21 μg/m 3 , 3.934 μg/m 3 , 0.9 mg/m 3 and 0.08 mg/m 3 from outside the excavator (underground excavation workshop), respectively. The EC and RCS concentration from outside the excavator is significantly higher than that of inside the excavator (p<0.01). The worksite with rock ground, higher vehicle density, blasting and enclosed environments had higher exposure to EC than other sites (p<0.05). There was no significant difference of EC concentration between total and respirable particulates. In top down construction sites, EC concentrations during underground excavation work exceeded recommended exposure limits as 20 μg/m 3 , accounted for about 50% of the total sample, and the level of concentration of RCS exceeded 1.5 times of occupational exposure limit, 0.05 mg/m 3 . Efforts are needed to minimize exposure to diesel engine exhaust and silica in underground excavation sites. Management of diesel engine vehicle, supply of fresh air and ventilation and introducing water facilities to create wet environment in underground worksites are strongly suggested.

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This commentary presents the regulatory backgrounds and development of the national proficiency testing (PT) scheme on asbestos analysis in the Republic of Korea. Since 2009, under the amended Occupational Safety and Health Act, the survey of asbestos in buildings and clearance test of asbestos removal works have been mandated to be carried out by the laboratories designated by the Ministry of Employment and Labor (MOEL) in the Republic of Korea. To assess the performance of asbestos laboratories, a PT scheme on asbestos analysis was launched by the Korea Occupational Safety and Health Agency (KOSHA) on behalf of the MOEL in 2007. Participating laboratories are evaluated once a year for fiber counting and bulk asbestos analysis by phase contrast microscopy and polarized light microscopy, respectively. Currently, the number of laboratory enrollments is > 200, and the percentage of passed laboratories is > 90. The current status and several significant changes in operation, sample preparations, and statistics of assigning the reference values of the KOSHA PT scheme on asbestos analysis are presented. Critical retrospect based on the experiences of operating the KOSHA PT scheme suggests considerations for developing a new national PT scheme for asbestos analysis.