Heat Stress White Papers

1. Cheuvront, Samuel N., et al. "Effect of WBGT Measurement Location on Heat Stress Category Classification." MEDICINE AND SCIENCE IN SPORTS AND EXERCISE. Vol. 46. No. 5. 530 WALNUT ST, PHILADELPHIA, PA 19106-3621 USA: LIPPINCOTT WILLIAMS & WILKINS, 2014.

Abstract: The location of the Wet Bulb Globe Temperature (WBGT) index measurement may impact heat stress flag category classification. PURPOSE: To compare WBGT measurements at three locations along the Boston Marathon race course and to compare each to WBGT estimates for meteorological stations and 72 hour advanced WBGT forecasts. METHODS: WBGT was measured hourly from 1000-1400 at ~7 km, ~18 km, and ~30 km on the Boston Marathon race course [Kestrel].  Simultaneous WBGT estimates were made for two meteorological stations southeast of the course via a commercial on-line system [Schneider Electric], which also provided 72 hour advanced forecasts.  RESULTS: Measurement differences (mean ± SD) among course locations was 0.2 ± 1.8°C WBGT (ANOVA, P>0.05).  Differences between course and meteorological stations was 1.9 ± 2.4°C WBGT (t-test, P<0.05).  Meteorological station values under-estimated (n = 98) or over-estimated (n = 13) course values by > 3°C WBGT (> ½ flag category) in 111/245 paired comparisons (45%).  Higher black globe and lower wet bulb temperatures explained over- and under-estimates, respectively.  Significant under-estimates of WBGT resulted in misclassification of green (labeled white) and black (labeled red) course flag categories (Χ2, P < 0.05).  Forecasted data significantly under-estimated red (labeled amber) and black (labeled red) course flag categories.  CONCLUSIONS:  This study suggests that differences in WBGT index along 23 km of the Boston Marathon race route can be small enough to warrant single measurements.  However, significant misclassification of flag categories occurred using WBGT estimates for meteorological stations, thus local measurements are preferred.  If the relationship between meteorological station WBGT forecasts and the race sites can be established using prior comparisons, the forecast WBGT values could be corrected to give advanced warning of approximate flag conditions.  Similar work is proposed for other venues to improve heat stress monitoring.

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