Table 1.

Restraints on Activities at Different Levels of Heat Stress

WBGTRestraints on Activities
°C°F
<24<75All activities allowed, but be alert for prodromes of heat-related illness in prolonged events
24.0–25.975.0–78.6Longer rest periods in the shade; enforce drinking every 15 minutes
26–29 79–84Stop activity of unacclimatized persons and other persons with high risk; limit activities of all others (disallow long-distance races, cut down further duration of other activities)
>29>85Cancel all athletic activities
  •  From the American Academy of Pediatrics, Committee on Sports Medicine and Fitness.16 WBGT isnot air temperature. It indicates wet bulb globe temperature, an index of climatic heat stress that can be measured on the field by the use of a psychrometer. This apparatus, available commercially, is composed of 3 thermometers. One (wet bulb [WB]) has a wet wick around it to monitor humidity. Another is inside a hollow black ball (globe [G]) to monitor radiation. The third is a simple thermometer (temperature [T]) to measure air temperature. The heat stress index is calculated as WBGT = 0.7 WB temp + 0.2 G temp + 0.1 T temp.

    It is noteworthy that 70% of the stress is due to humidity, 20% to radiation, and only 10% to air temperature.