The use of sun-shade on safe heat exposure limit on a sunny summer day: a modelling study in Japan.

Abstract

Sustainable methods are required to reduce the risks of thermal strain and heat-related illness without exacerbating greenhouse gas emissions. We investigated the effects of sun-shade use on safe heat exposure limit on a sunny summer day using historical climate data in Japan. We simulated a heat-acclimatised person standing at rest (metabolic heat production, 70W·m-2) and during light work (100W·m-2) on an asphalt pavement in the sun and sun-shade. Japan has three Köppen climate regions: tropical, temperate and cold. We analysed one city in the tropical region (24°N), three cities in the temperate region (31°N, 35°N and 39°N) and one city in the cold region (40°N). Hourly data were collected from 7 AM to 6 PM, June to September, from 2010 to 2019. The day with the longest daylight hours and the greatest solar radiation intensity was used for analysis. With sun-shade (a white polyester tarpaulin/awning), ambient temperature, global solar radiation and ground surface temperature were assumed to be 0.5°C, 45% and 6°C lower than in the sun, respectively. Sun-shade use eliminated the days with at least 1hour exceeding safe heat exposure limit at rest in all cities. The same was observed for light work in the temperate and cold cities, although the tropical city had 2days exceeding safe heat exposure limit during the decade. Sun-shade use on a sunny summer day can be an effective and sustainable method to reduce heat exposure hazard at rest and during light work in tropical, temperate and cold climate regions.