WBGT is a composite index of heat stress. Which formula correctly represents WBGT as a weighted sum of temperatures?

• A. 0.7 × wet-bulb temperature + 0.2 × globe temperature + 0.1 × dry-bulb (air) temperature
• B. 0.5 × dry-bulb + 0.3 × wet-bulb + 0.2 × globe
• C. 0.4 × globe temperature + 0.6 × wet-bulb temperature + 0.0 × dry-bulb temperature
• D. 1.0 × dry-bulb temperature

Answer: (A)

WBGT combines three temperature measures to reflect different ways heat affects the body: evaporative cooling, radiant heat, and ambient air heat. In outdoor settings, the standard WBGT is 0.7 times the wet-bulb temperature, plus 0.2 times the globe temperature, plus 0.1 times the dry-bulb (air) temperature. The largest weight on the wet-bulb temperature recognizes that humidity and the body's ability to evaporate sweat largely control heat stress. The globe temperature captures radiant heat from the sun and surroundings, which can substantially raise body temperature even if the air is not extremely hot. The dry-bulb temperature is included but with the smallest weight because air temperature alone doesn’t fully represent how heat stress progresses when evaporation and radiation are significant.

Other formulas either undervalue or omit these influences, leading to less accurate assessments of heat stress.