The National Weather Service is adopting wet bulb globe temperature (WBGT) as its new heat danger metric, revealing that dangerous heat conditions occur at much lower temperatures than traditional heat index suggests — especially in humid climates.
What Changes
A WBGT of 90°F can be lethal for outdoor workers, even when the air temperature is only 85°F if humidity is high. Traditional heat index underestimates danger in humid conditions by up to 15°F.
Who's at Risk
Construction workers, athletes, military personnel, and agricultural workers face the highest risk. The new metric will trigger workplace heat safety requirements at lower temperatures.
- WBGT replaces heat index as standard
- Danger at 85°F air temp in high humidity
- Traditional index underestimates by 15°F
- Workplace safety thresholds lowered
