WBGT

WBGT stands for Wet-Bulb Globe Temperature. It is a composite index used to estimate heat stress in direct sunlight and indoor heat conditions. The index combines several environmental cues that influence thermal strain, including ambient air temperature, humidity, radiant heat, and air movement. WBGT is widely used in occupational safety, sports, and military contexts to inform work-rest cycles, hydration strategies, and cooling measures.

Calculation and components: WBGT is derived from three measurements: dry-bulb temperature (Tdb), representing ambient air temperature; wet-bulb temperature (Twb), measured with a wick-covered thermometer and representing evaporative cooling; and globe temperature (Tg), measured with a black globe thermometer to capture radiant heat. A commonly cited formula for outdoor conditions with solar radiation is WBGT = 0.7*Twb + 0.2*Tg + 0.1*Tdb. Indoor or shaded conditions may use different weighting. In practice, WBGT can be measured directly with specialized devices or estimated from meteorological data and local measurements.

Measurement methods: Three instruments are used to capture the inputs: a sling psychrometer or aspirated thermometer for Twb, a globe thermometer for Tg, and a dry-bulb thermometer for Tdb. Measurements should be taken at or near the activity area and reflect the conditions experienced by individuals. Some weather services publish WBGT values during heat events to aid planning.

Applications and interpretation: WBGT guides heat-stress management, including hydration, cooling, pace adjustments, rest breaks, clothing choices, and training modifications. Higher WBGT values indicate greater heat stress and usually warrant stricter precautions and shorter exposure times. While useful, WBGT is an index with limitations and should be considered alongside workload, acclimatization, clothing, and individual risk factors.