The study population comprised workers exposed to cold work environments who worked in two frozen food factories in Rayong Province, Thailand. The study participants were calculated using the formula for simple logistic regression analysis [14], where n was the sample size required, P was the rate of the event based on Lekcharoen et al [15] who found that the proportion of workers who were exposed to cold frequently for more than 3 hours a day was 61.4% (p ¼ 0.614) and P1 P2 is the difference of the event between physical hazard exposed and nonexposed groups in which the minimum difference was 0.15