WetBulb Globe Temperatuere


The WetBulb Globe Temperature (WBGT) is a measure of the heat stress in direct sunlight which takes into account; temperature, humidity, wind speed, sun angle and cloud cover (solar radiation). This differs from the heat index which takes into consideration temperature and humidity and is calculated for shady areas. If you work or exercise in direct sunlight, this is a good element to monitor. Military agencies, OSHA and many nations use the WBGT as a guide to managing workload in direct sunlight.
wbgt heatIndex
WetBulb Globe Temperature Heat Index

Comparison with Heat Index

 
WBGT
Heat Index
Measured in the sun
Measured in the shade
Uses Temperature
Uses RH
Uses Wind
Uses Cloud Cover
Uses Sun Angle

Examples

Temp F Dwpt F RH % Sky % Wind mph HeatIdx F WBGT F
90 65 42 05 03 92 89
90 65 42 05 13 92 83
90 65 42 65 13 92 81
90 70 52 10 06 96 88
90 70 52 60 06 96 86
90 70 52 60 13 96 85
100 70 39 10 13 108 90
100 70 39 10 5 108 94
100 70 39 65 05 108 91

 



Preparedness - What to do before doing outdoor activities when the WBGT is high -
  • Wear a hat and light weight, light fitting, light colored clothes.
  • Plan to take frequent breaks in shady areas.


  • Safety - What to do while doing outdoor activities when the WBGT is high -
  • Take breaks in the shade. Strenuous outdoor activities should be reduced, especially in direct sunlight where there is little ventilation.
  • Drink plenty of water or other non-alcohol fluids. Your body needs water to keep cool. Drink plenty of fluids even if you don’t feel thirsty.
  • Don’t get too much sun. Sunburn makes the job of heat dissipation that much more difficult
  • Other Resources
    More WBGT Information
    WBGT Research Paper
    OSHA work load and WBGT Manual

    Suggested Actions and Impact Prevention
    Degs F
    Affects
    Precautionary Actions
    < 80

    80-85 Working or exercising in direct sunlight will stress your body after 45 minutes. Take at least 15 minutes of breaks each hour if working or exercising in direct sunlight
    85-87 Working or exercising in direct sunlight will stress your body after 30 minutes. Take at least 30 minutes of breaks each hour if working or exercising in direct sunlight
    88-90 Working or exercising in direct sunlight will stress your body after 20 minutes. Take at least 40 minutes of breaks each hour if working or exercising in direct sunlight
    >90 Working or exercising in direct sunlight will stress your body after 15 minutes. Take at least 45 minutes of breaks each hour if working or exercising in direct sunlight

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