[Worker heat disorders at the Fukushima Daiichi nuclear power plant]

Ever since the Fukushima Daiichi nuclear power plant (NPP) accident, every day about 3,000 workers have been working to repair the situation. The frequent occurrence of heat disorders has been a concern for the workers wearing protective clothing with poor ventilation. We have been analyzing the heat disorder problem since the accident in order to come up with a solution to prevent future heat disorder incidents among Fukushima Daiichi NPP accident clean-up workers.

From March 22 to September 16, 2011, the Fukushima Labor Bureau assessed 43 cases of nuclear power plant workers with heat disorders. Age of subject, month and time of occurrence, temperature, and humidity were examined for each case, as well as the severity of heat disorders. The grade of severity was divided into Grade I and Grade II or higher. Then, age, temperature, and humidity were analyzed using the Mann-Whitney Utest, and age, temperature, humidity, and presence or absence of a cool-vest were analyzed using the χ(2) test and logistic regression analysis. SPSS version 17.0 statistical software was used with a level of significance of p< 0.05.

Heat disorders occurred most frequently in subjects in their 40s (30.2%), followed by those in their 30s (25.6%), mostly in July (46.5%) between 7 am and 12 pm (69.8%). Heat disorders occurred most frequently in environments with temperatures more than 25°C (76.7%) and humidity of 70-80% (39.5%). Heat disorders of Grade II or higher occurred in 10 cases, 5 of which were in June. According to statistical analysis, there were no significant differences in difference of severity for all factors.

Heat disorders usually occur in workers aged 45-60; however, cases of heat disorders at the Fukushima Daiichi NPP occurred in clean-up workers at the relatively younger ages of 30-40, suggesting the need for heat disorder prevention measures for these younger workers. Heat disorder cases primarily occurred in the morning, necessitating preventive measures for the early hours of the day. In addition, because heat disorders of Grade II or higher occurred in June in 5 of 10 cases, we believe heat disorder precautions should be implemented from June. The lack of significant difference in severity difference may be attributable to the small number of cases or other factors. We think Fukushima Daiichi NPP accident clean-up workers need heat disorder prevention measures for their safety, based on the results of this study.