Field-based Heatwave Risk Assessment of Outdoor Workers Measured by Wearable Sensors

Abstract

Increasing heatwave frequency due to climate change threatens outdoor workers’ health. We aimed to assess the on-site heat strain level of outdoor workers using wearable sensors and identify the factors for consideration in developing individual-based heat adaptation strategies. Seven road construction workers were recruited and asked to wear necklace-form temperature loggers and smartwatches monitoring heart rate (HR). The questionnaire was delivered daily to ask about their psychological comfort level during work. Workers were exposed to up to 5.4 °C higher temperature than the official air temperature, indicating that the national heatwave alarm does not reflect on-site heat conditions. Based on the measured HR data, heat strain levels were defined. When HR exceeded the level of “180-age,” we assumed extreme heat strain occurred, which requires immediate cessation of work. When HR exceeded 40% of the individual heart rate reserve (the difference between the maximum and resting HR), we assumed high heat strain occurred, indicating a stressed condition. High heat strain occurred in all workers on 9 of the 13 monitored days, whereas the official heatwave alarms were issued only on four dates. Additionally, three workers experienced extreme heat strain on two dates. The main factor for workers experiencing extreme heat strain was age. Comparing the heat strain levels from HR with the survey results, we found that the older workers considered their condition comfortable even under extreme and high heat strain. Thus, an individual sensor-based early-warning system is needed to prevent heat strain not perceived by outdoor workers. The findings emphasize the need for a personalized adaptation strategy for heatwaves and will be a baseline for developing a new work manual that mainstreams climate change impacts.