Night work is defined as a harmful factor in Article 130 (special health diagnosis) of the Occupational Safety and Health Act and is defined as performing eight-hour tasks that continue more than four times a month, including the time from 12 p.m. to ...
Night work is defined as a harmful factor in Article 130 (special health diagnosis) of the Occupational Safety and Health Act and is defined as performing eight-hour tasks that continue more than four times a month, including the time from 12 p.m. to 5 a.m. the next day, or performing tasks more than 60 hours a month during the time between 10 p.m. and 6 a.m. the next day.
The problem with night work is that it may increase the risk of accidents due to decreased arousal, accumulated fatigue, and lack of recovery time as workers work at the time they need to sleep normally. However, there is a lack of research in previous studies to identify harmful factors and health problems of night workers or to verify the indirect effect (mediated effect) of sleep problems in these relationships. Therefore, the purpose of this paper is to verify the direct effect of exposure to harmful factors of night workers on health problems and indirect effects through sleep problems, and to suggest working environment and health protection measures.
Using the data from the 7th Korean Working Conditions Survey(2023), this paper selected 1,140 workers who met the night work standards of Article 130(special health examination) of the Occupational Safety and Health Act. Research variables consisted of independent variables (exposure of physical, musculoskeletal, and psychological harmful factors), dependent variables (physical and mental health problems), and parameters (sleep problems). As a research method, comparison of exposure to harmful factors between night and day workers, analysis of differences in exposure to harmful factors and health problems according to general characteristics, direct effect of exposure to harmful factors on health problems, and analysis of mediating effects of sleep problems were performed. For statistical analysis, frequency analysis, independent sample t-test, one-way ANOVA, Pearson correlation analysis, and multiple regression analysis were performed using SPSS 29.0, and bootstrapping(5,000 times) was performed using PROCESS Macro Model 4.
As a result of the study, night workers had significantly higher exposure to physical hazards (1.30 vs. 1.03), musculoskeletal hazards (3.16 vs. 2.92), and psychological hazards (1.29 vs. 0.89), compared to daytime workers (p<.001). In terms of gender differences, women had higher exposure to musculoskeletal hazards (p=.004), psychological hazards (p<.001), physical health problems (p<.001), and mental health problems (p<.001) than men. By age, physical health problems were the highest in those over 60 years of age (p<.001), and physical health problems (3.47 points) of long-term service workers over 30 years of age were about 1.7 times higher than those of those with less than 10 years of service (2.05 points). By job type, production workers had high exposure to physical hazards (p<.001) and physical and mental health problems (p<.05) while service workers had high exposure to musculoskeletal and psychological hazards (p<.001) and sleep problems (p=.023). By industry, exposure to physical hazards was high in production and manufacturing (p<.001), and exposure to musculoskeletal and psychological hazards was the highest in public, health and education (p<.001). As a result of direct effect analysis, physical hazard exposure (β=0.08, p=.015) and musculoskeletal hazard exposure (β=0.13, p<.001) had a significant effect on physical health problems, but psychological hazard exposure had no significant effect (β=0.03, p=.280). Physical hazard exposure (β=0.08, p=.031), musculoskeletal hazard exposure (β=0.07, p=.041), and psychological hazard exposure (β=0.10, p=.003) all had significant effects on mental health problems. As a result of mediating effect analysis, physical hazard exposure had no significant effect on sleep problems (B=.016, p=.150). Musculoskeletal hazard exposure had a significant effect on sleep problems (B=.058, p<.001), and physical health problems (indirect effects=.022, 95% CI: .010~.036) and mental health problems (indirect effects=.012, 95% CI: .005~.019) were found to be partially mediated. Psychological hazard exposure had the strongest effect on sleep problems (B=.090, p<.001) and completely mediated (indirect effects=.034, 95% CI: .019 to .052) and partial mediation (indirect effect =.018, 95% CI: .009 to .029) in mental health problems.
Based on these findings, suggestions for institutional improvement measures to protect the health of night workers are as follows. First, considering that physical harmful factors directly affected health regardless of sleep problems, a system for exposure standards and time to harmful factors at night is needed. The current Labor Standards Act only stipulates the obligation to pay additional wages for night work, and there is no limit on the night work hours themselves, so night work is possible within the range of 52 hours a week. On the other hand, Germany's working hours law limits the daily working hours of night workers to 8 hours, but allows an extension of up to 10 hours under the condition that the average of one month or four weeks does not exceed 8 hours. The French labor law also stipulates that the average working hours per week for 12 consecutive weeks cannot exceed 40 hours in principle. As such, developed countries have a flexible regulatory system that allows limited extensions on the condition of compliance with average working hours while specifying a daily upper limit of night work, so an institutional review is needed in Korea with this reference. Second, workers working at night showed high musculoskeletal symptoms and mental health problems, but since the relevant evaluation items are insufficient in the current special health diagnosis, it is necessary to review the addition of musculoskeletal symptoms and job stress evaluation items. Third, it is necessary to consider shortening the health examination cycle and guaranteeing the right to request switching to daytime work for the vulnerable group as in Germany, taking into account the higher health problems of women and older workers. Fourth, as sleep problems have been identified as a key pathway between exposure to harmful factors and health problems, it is necessary to give institutional coercion to follow-up management measures centered on sleep management, such as reducing the number of late-night businesses and switching to daytime work, as in Japan's Labor Safety and Sanitation Act. Fifth, in relation to the protection of workers at night in small workplaces, this study showed the highest exposure of psychological harmful factors and sleep problems of workers at small workplaces, so it is necessary to strengthen access to special health diagnosis for workers at night in workplaces with fewer than 5 employees in legal blind spots. Sixth, in relation to the preparation of standards for measuring the working environment at night hours, this study found that exposure to physical harmful factors had a direct effect on health problems, so it is necessary to prepare standards for exposure to physical harmful factors and illuminance standards for each time period considering the specificity of night work. Such institutional improvements will contribute to protecting the health of night workers and establishing a prevention-oriented management system.