Wet Bulb Globe Temperature

Wet Bulb Globe Temperature

Map, calculator courtesy National Weather Service - Tulsa

MAPS

Wet Bulb Globe Temps

7 am

10 am

1 pm

4 pm

7 pm

Heat Index

7 am

10 am

1 pm

4 pm

7 pm

Wet Bulb Globe Temperature vs Heat Index

While the WBGT and Heat Index both attempt to describe how "hot" it is and the potential for heat related stresses, they go about it in different ways.

â–º Heat Index is more commonly used and understood by the general public - the higher the values the hotter it's going to feel and the higher the threat for heat related illnesses. It's calculated from the temperature and relative humidity. What's not commonly known is that Heat Index assumes you are in the shade. 

â–º WBGT also uses the temperature and humidity in its calculation, but temperatures are measured in direct sunshine. It also factors in wind speed, sun angle, and cloud cover.  

Bottom-line upfront >>>> what value should you use? For day-to-day activities, heat index will serve you well. If you work outside or plan on any sort of vigorous outdoor activity in the full sun, use the WBGT.  

Comparing WBGT and 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 Dew Point F RH % Sky % Wind mph Heat Index 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

PREPARE - SAFETY - RESOURCES

Prepare

Before:

• Reschedule or postpone outdoor plans during peak heating of the day (usually mid to late afternoon)
• Check in with family members, friends. Make sure they have a way to keep cool and take necessary precautions from the heat. The elderly and children are especially susceptible to the heat. 
• Don't forget your pets! Make sure they have adequate shelter (preferably indoors, air conditioned) and ample water. 

During:

• Take frequent breaks in the shade or in an air conditioned location. Strenuous outdoor activities should be reduced (or eliminated), especially in direct sunlight where there is little ventilation.
• Drink plenty of water or other non-alcohol fluids. Stay hydrated by drinking plenty of fluids even if you do not feel thirsty. Avoid drinks with caffeine or alcohol.
• Continue to check on family, friends and your pets. 
• Don’t get too much sun. Sunburn makes the job of heat dissipation that much more difficult

Resources

• General WBGT Information (Wiki page)
• American College of Sports Medicine (ACSM), [position stand]
• Korey Stringer Institute
• University of Georgia Research [AMS conference presentation]
• WBGT Research
• OSHA Heat Hazard Assessment and WBGT
• Department of the Army: Prevention of Heat and Cold Casualties
• Department of the Army: WBGT, Guidelines, Prevention

Guidelines - Charts

While there is not set criterion for WBGT temperatures and related risks/impacts, the American College of Sports Medicine (ACSM) has developed a set of values that have been accepted as a standard to follow. Their original guidelines were developed for running events, but have since been expanded to include intermittent (non-continuous) activities [Medicine & Science in Sports & Exercise: March 2007 - Volume 39 - Issue 3 - p 556-572] . The guidelines are not based on location.

Using ACSM as a starting point, further research by the University of Georgia (UGA) factored in climatology and regional differences in an effort to incorporate acclimatization* into the guidelines. The Korey Stringer Institute and USA Soccer used the regional categories developed by UGA to provide another set of recommend actions.

The military and OSHA also have devised recommendations, as do many university and high school athletic departments.

Below you will find several of these guidelines/recommendations.  

It should be noted that while WBGT will provide solid guidelines, other factors such as an individual’s physical fitness, acclimatization, medical condition, and age also have an impact.

* Acclimatization: the body's natural adaptation to heat/cold. The process usually takes 10 to 14 days.

NOT based on location - American College of Sports Medicine

Continuous Activities		Intermittent Activities
Activities with little if any break, such as cross country running, 5K runs, and marathons.		Activities that generally have breaks between bursts of high intensity movements/actions, such as football, soccer, lacrosse, etc.
Guidelines from the American College of Sports Medicine - not based on location		Guidelines from the American College of Sports Medicine - not based on location

Based On Location

The following recommendations use similar criteria as the ACSM, but modified for location and climatology. This adjustment factors in the acclimatization that occurs for those that consistently work and exercise in hot environments.

Regional Categories

Guidelines from USA Soccer and the Korey Stringer Institute (KSI)		Guidelines from the University of Georgia

Other Charts For Reference