Digital Heat Stress Monitoring in Outdoor Work Environments: Validation and Practical Implications of Mobile Application-Based WBGT Estimation

Abstract

The growing availability of smartphone-based applications to monitor heat stress provides opportunities to democratize thermal risk assessment in workplaces where the use of the wet-bulb globe temperature instrumentation is economically or logistically expensive. This future field study confirmed the AIHA Heat Stress App 2.0 with calibrated 3M QUESTemp 34 reference monitoring in a range of outdoor thermal environments over an 18-day time span in a subtropical climate area. The 53 paired measurement sessions recorded a significant environmental variation with a reference WBGT between 19.8°C and 39.4°C. The mobile application displayed temporal concordance over reference measurements in tracing the patterns of heat stresses over the day but systematic negative bias with average of -1.7°C and standard deviation of 2.1°C. Differences became very large in the conditions of high solar radiation (1200-1500 hours) when reference WBGT was close to or above the regulations (up to 7.4 C) and single-session underestimation was at the highest point (7.4°C). The misclassification of the work-rest category was seen in 35.8 percent of the paired measurements in the majority of them being underscoring the risk. Findings are in favor of a hybridized monitoring system whereby smartphone applications offer the availability of preliminary screening and yet being anchored by calibrated instruments, precision-critical decisions in the form of compliance checks and high-risk expos