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WetBulb Globe Temperatuere

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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.

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