Comparison between WBGT app prototype and WBGT monitor to assess heat stress risk in an eastern North Carolina outdoor setting.

Abstract

The wet bulb globe temperature (WBGT) index is the preferred environmental heat metric for occupational heat-related illness prevention but may not always be readily accessible in the workplace. Thus, there is a need for well-designed WBGT-based tools that are reliable, accessible, and inexpensive. A novel WBGT app prototype was developed to calculate the current and forecasted outdoor WBGT. The purpose of this study was to assess the reliability of the WBGT app prototype in providing accurate heat stress risk information for outdoor workplace settings in eastern North Carolina by comparing the WBGT indices and risk levels from the app (WBGT_app) with those derived from a heat stress monitor (WBGT_ins). Outdoor WBGT measurements were data logged at a university campus site using a heat stress monitor from March to August 2023 for 81 days and were assigned to risk levels by workload based on the ACGIH Threshold Limit Values. Hourly WBGT_app values and their corresponding risk levels were obtained using the app prototype. Data analysis was conducted using a t-test, Pearson correlation test, and cross-tabulation. Results showed that the hourly mean WBGT_app was significantly higher (p < 0.01) than the WBGT_ins, but there was no significant difference between the overall average of the daily mean (p = 0.15) and daily maximum (p = 0.69) WBGT_app and WBGT_ins. There was a strong, positive correlation between the hourly mean (r = 0.94, p < 0.01), daily mean (r = 0.97, p < 0.01), and daily maximum (r = 0.94, p < 0.01) WBGT_app and WBGT_ins. The app correctly identified 73-88% of minimal-risk conditions, depending on workload type, and was most reliable in correctly identifying extreme-risk conditions at 97%, 95%, and 93% for light, moderate, and heavy workloads, respectively. This demonstrates the app's capability of being protective of the workers, particularly in more severe heat stress risk conditions. Recommendations to improve the app's accuracy involved using accurate solar irradiance data and applying linear calibration. The WBGT app prototype shows good potential as an alternative risk assessment tool for heat stress risk among outdoor workers.