An Evaluation of Portable Wet Bulb Globe Temperature Monitor Accuracy

Context: Wet bulb globe temperature (WBGT) is the gold standard for assessing environmental heat stress during physical activity. Many manufacturers of commercially available instruments fail to report WBGT accuracy. Objective: To determine the accuracy of several commercially available WBGT monitors compared with a standardized reference device. Design: Observational study. Setting: Field test. Patients or Other Participants: Six commercially available WBGT devices. Main Outcome Measure(s): Data were recorded for 3 sessions (1 in the morning and 2 in the afternoon) at 2-minute intervals for at least 2 hours. Mean absolute error (MAE), root mean square error (RMSE), mean bias error (MBE), and the Pearson correlation coefficient (r) were calculated to determine instrument performance compared with the reference unit. Results: The QUESTemp8 34 (MAE = 0.248C, RMSE = 0.448 degrees C, MBE = -0.64%) and Extech HT30 Heat Stress Wet Bulb Globe Temperature Meter (Extech; MAE = 0.618 degrees C, RMSE = 0.798 degrees C, MBE = 0.44%) demonstrated the least error in relation to the reference standard, whereas the General WBGT8778 Heat Index Checker (General; MAE = 1.188 degrees C, RMSE = 1.348 degrees C, MBE = 4.25%) performed the poorest. The QUESTemp8 34 and Kestrel 4400 Heat Stress Tracker units provided conservative measurements that slightly overestimated the WBGT provided by the reference unit. Finally, instruments using the psychrometric wet bulb temperature (General, REED Heat Index WBGT Meter, and WBGT-103 Heat Stroke Checker) tended to underestimate the WBGT, and the resulting values more frequently fell into WBGT-based activity categories with fewer restrictions as defined by the American College of Sports Medicine. Conclusions: The QUESTemp8 34, followed by the Extech, had the smallest error compared with the reference unit. Moreover, the QUESTemp8 34, Extech, and Kestrel units appeared to offer conservative yet accurate assessments of the WBGT, potentially minimizing the risk of allowing physical activity to continue in stressful heat environments. Instruments using the psychrometric wet bulb temperature tended to underestimate WBGT under low wind-speed conditions. Accurate WBGT interpretations are important to enable clinicians to guide activities in hot and humid weather conditions.