Aug 7, 2019WBGT: Recommended Measurement for Preventing Heat Stress
Exertional heat stress poses a serious risk to people expected to practice or perform in environments where hot and humid conditions exist.
There’s no question that heat stress remains a top concern for athletic training professionals. Heat stress presents many symptoms and encompasses several heat-induced illnesses such as heat stroke, heat exhaustion, heat cramps and heat rashes. These conditions are more likely to occur during hot weather and the severity of symptoms depends upon the level of athlete acclimatization and onsite microclimate conditions, but may also affect athletes in milder conditions year round. The recommended measurement used to determine actual environmental heat stress and assessment for heat stress risk is Wet Bulb Globe Temperature or “WBGT.”
How is Wet Bulb Globe Temperature Calculated?
To calculate WBGT, you will need: wet bulb temperature (Tw), globe temperature (Tg), and dry bulb temperature (Td). Wet bulb temperature is a measurement of humidity, globe temperature is a measurement for amount of solar radiation, and dry bulb temperature is a measurement for air temperature. In addition, wet bulb temperature and globe temperature are influenced by wind speed. WBGT equation weighs heavily on the Tw (70%) because the air saturation dictates the capacity for the body heat dissipation through sweat evaporation. Since evaporative heat loss accounts for the majority heat dissipation during exercise, an environment that hinders this process will pose an extreme heat strain.
Athletic Surfaces & Heat Stress Risk: All Playing Fields Are Not Created Equal
Weather apps miss the mark when it comes to providing microclimate data. To assess the real risk of exertional heat stress, onsite WBGT measurement is the gold standard for accuracy. There can be multiple microclimates on a school campus based on the athletic surfaces and variations in temperature, humidity, pressure, wind, sun, shade and reflected/radiant heat. Different types of athletic surfaces result in varying risk levels of heat stress due to the surface itself and the impact of external environmental factors. A 2017 study published in the Journal of Athletic Training shared research findings detailing the disparity between National Weather Service predictive measurements vs the actual, observed onsite WBGT measurements of athletic surfaces.
“WBGT measurements should be taken at regular intervals on each outdoor athletic playing surface to adequately capture the environmental conditions affecting physical performance and the risk of exertional heat illness.”
Key Study Findings
- Using National Weather Service wet-bulb globe temperature (WBGT) resulted in heat-safety category misclassification across all athletic surfaces.
- The National Weather Service WBGT underestimated the local athletic-surface heat stress, especially when the surface was black or red or made of synthetic material.
- Onsite WBGT measurement remains a prudent choice for determining environmental conditions and the need for heat-safety physical-activity modifications or cancellations.
“The Heat Strain of Various Athletic Surfaces: A
Comparison Between Observed and Modeled Wet-Bulb
J. Luke Pryor, PhD, ATC, CSCS*†‡; Riana R. Pryor, PhD, ATC*†‡;
Andrew Grundstein, PhD; Douglas J. Casa, PhD, ATC, FNATA, FACSM‡
Journal of Athletic Training; Volume 52, Number 11, November 2017
About Kestrel Instruments
Kestrel Meters are used by athletic trainers and professionals to monitor the health and safety of the athletes under their direction. Further, athletic trainers can set the device to store data at specific time intervals and then send the information to their smartphones—making it easier to document, store, and share readings. Trainers are able to conveniently access pre-programmed zones for NATA, ASCM and several state athletics guidelines in the Kestrel 5400 Heat Stress Tracker unit. All of Kestrel’s products are made in the U.S.A and come with a five-year warranty.