Wet bulb globe temperature (WBGT)
A heat index that combines air temperature, humidity and radiant heat to estimate the thermal load on a person.
Definition, in the source's words
NIOSH, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (Pub. 2016-106), Glossary(opens cdc.gov in a new tab)“This is an environmental temperature arrived at by measuring dry air temperature, humidity, and radiant energy (i.e., usually direct sunlight being absorbed by clothing), used to calculate a thermal load on the person.”
What it means
Indoors or without sun: WBGT = 0.7 × natural wet bulb + 0.3 × globe. Outdoors in sun: WBGT = 0.7 × natural wet bulb + 0.2 × globe + 0.1 × dry bulb.
Example
Outdoors in sun: natural wet bulb 78°F, globe 100°F, dry bulb 90°F. WBGT = 0.7 × 78 + 0.2 × 100 + 0.1 × 90 = 54.6 + 20 + 9 = 83.6°F.
Where it appears on the exam
ASP: ASP11 Domain 6, Industrial Hygiene and Occupational Health
Practice: Heat Stress (NIOSH Criteria), Heat Index, WBGT and Wind Chill Calculations
CSP: CSP11 Domain 6, Occupational Health and Applied Science
CHST: CHST5 Domain 2, Emergency Preparedness, Incident Investigation, and Response
Practice: Heat Illness Prevention and First Response, Heat Index, WBGT and Wind Chill
Questions
- Why does the outdoor WBGT formula include dry bulb temperature?
- The outdoor version adds 0.1 × dry bulb and lowers the globe weight to 0.2 to account for direct sun.
Related
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