Spatio-temporal patterns of the minimum rest time for outdoor workers exposed to summer heat stress in South Korea.

In this study, the spatio-temporal characteristics of the minimum rest time for the safety of South Korean outdoor workers during hot summer months (June to August) are examined based on the hourly wet-bulb globe temperature (WBGT) across 27 weather stations in South Korea. The WBGT thresholds in the work-rest recommendation of the Korea Occupational Safety and Health Agency (KOSHA 2017) for the quantification of the minimum rest time are evaluated through a comparison of the given thresholds with the occurrences of occupational heat-related illness patients due to outdoor work during hot summer months in South Korea. The long-term (2009-2018) average of the hourly WBGT values during summer months shows that outdoor workers with a moderate workload are exposed to heat stress during approximately 30% of the entire daytime working hours (06:00-18:00). According to the WBGT thresholds modified from the KOSHA (2017) guidelines, the daily minimum rest time for a moderate workload noticeably increases up to 18% (11 min/h) in mid-summer (late July and early August). During mid-summer, the minimum rest time for a continuous moderate outdoor workload even increases up to 31% (18 min/h) between 12:00 and 13:00 and is regionally higher in the southwestern than in the southeastern regions of the Korean Peninsula. These results suggest that in summertime high-heat environments, a mandatory rest time must be provided according to appropriate heat management programs for the safety of workers.

Changing human-sensible temperature in Korea under a warmer monsoon climate over the last 100 years.

This study explores changes in means and extreme events of human-sensible temperature (HST), which is quantified by selective combination of Universal Apparent Temperature, Heat Index, and a new Wind Chill Index, in Korea for the last 100 years (1919-2018) and illustrates the synoptic patterns of the East Asian monsoon system (EAMS) for extreme HST events. The time series analyses show that HST has increased much faster than near-surface air temperature (AT) in winter due to decrease in wind chill as well as to increase in AT. On the other hand, HST in summer, which is higher than AT on average because of high humidity in monsoon climate, has increased at a slow rate compared with those in other seasons. However, more extremely hot, long-lasting HST events have been observed in recent decades, as in 1994, 2013, 2016, and 2018, with shorter recurrent intervals. Greater increases of HST than AT are more distinct in the southern region under maritime subtropical climate than in the temperate climate zone in the north in all seasons. Composite maps for multiple high or low HST extreme events reveal that a dipole pressure anomaly pattern, rather than the intensity at the center of these air masses, is more closely related to the frequency of extreme HST events in Korea: A west high-east low pattern in winter formed by the expansion of the Siberian High accompanying an intense migratory low pressure system, and a south high-north low pattern formed by the westward intrusion of the Northwest Pacific subtropical high in summer after earlier terminations of summer rainy period (Changma). These indicate that monitoring of changing EAMS's characteristics is crucial to the mitigation of potential damages caused by unprecedented HST extreme events in the warmer twenty-first century.

[The impact of high apparent temperature on the increase of Summertime Disease-related mortality in Seoul: 1991-2000].

OBJECTIVES: The aim of this paper was to examine the relationship between the summertime (June to August) heat index, which quantifies the bioclimatic apparent temperature in sultry weather, and the daily disease-related mortality in Seoul for the period from 1991 to 2000. METHODS: The daily maximum (or minimum) summertime heat indices, which show synergetic apparent temperatures, were calculated from the six hourly temperatures and real time humidity data for Seoul from 1991 to 2000. The disease-related daily mortality was extracted with respect to types of disease, age and sex, etc. and compared with the time series of the daily heat indices. RESULTS: The summertime mortality in 1994 exceeded the normal by 626 persons. Specifically, blood circulation-related and cancer-related mortalities increased in 1994 by 29.7% (224 persons) and 15.4% (107 persons), respectively, compared with those in 1993. Elderly persons, those above 65 years, were shown to be highly susceptible to strong heat waves, whereas the other age and sex-based groups showed no significant difference in mortality. In particular, a heat wave episode on the 22nd of July 2004 (> 45 degrees C daily heat index) resulted in double the normal number of mortalities after a lag time of 3 days. Specifically, blood circulation-related mortalities, such as cerebral infraction, were predominant causes. Overall, a critical mortality threshold was reached when the heat index exceeded approximately 37 degrees C, which corresponds to human body temperature. A linear regression model based on the heat indices above 37 degrees C, with a 3 day lag time, accounted for 63% of the abnormally increased mortality (> or =+2 standard deviations). CONCLUSIONS: This study revealed that elderly persons, those over 65 years old, are more vulnerable to mortality due to abnormal heat waves in Seoul, Korea. When the daily maximum heat index exceeds approximately 37 degrees C, blood circulation-related mortality significantly increases. A linear regression model, with respect to lag-time, showed that the heat index based on a human model is a more dependable indicator for the prediction of hot weather-related mortality than the ambient air temperature.