1. a Department of Occupational and Environmental Health , The Graduate School of Public Health, Seoul National University , Seoul , Korea
2. b Department of Occupational and Environmental Medicine , Dankook University Medical College , Cheonan , Korea
3. c Department of Preventive Medicine , Ewha Womans University School of Medicine , Seoul , Korea
4. d Department of Industrial and Information Systems Engineering , Ajou University , Suwon , Korea
5. e Department of Safety Engineering , Hankyong National University , Anseong , Korea