Wet Bulb Globe Temperature

Other Names

• Wet Bulb Globe Temperature (WBGT)

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Definition

• Wet Bulb Globe Temperature: measure of the heat stress in direct sunlight, which takes into account: temperature, humidity, wind speed, sun angle and cloud cover
  • Used by employers, athletes, sporting events and military to determine appropriate exposure levels to high temperatures
  • Can reliably predict environmental heat stress

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Table of alert levels and recommendations

ACSM 5 Colored Flags

• Black flag level: WBGT greater than 82°F (28°C),
  • races should be cancelled or recommends voluntary withdrawal
  • Races that are always held in these conditions should acknowledge the extreme heat risk to the poorly acclimated and non-resident competitors
  • Announcement should be in the pre-race literature and the pre-race announcements
• Red flag level: WBGT is between 73°F to 82°F (23°C to 28°C).
  • Participants who are at increased risk for heat collapse are recommended to withdraw from the race
  • It is recommended that all other participants slow their pace to match the conditions
• Yellow flag level: WBGT between 65°F to 72°F (18°C to 22°C).
  • ACSM recommends that participants at increased risk for heat collapse slow their pace
  • Entrants should be warned of increased risk of heat collapse
• Green flag level: WBGT less than 65°F (18°C).
  • Although collapse can still occur, there is a decreased risk of hyperthermic and hypothermic collapse
  • This is an ideal level for a marathon
• White flag level: WBGT less than 50°F (10°C).
  • There is increased risk of hypothermic collapse
  • participants should be advised to wear appropriate clothing

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See Also

• Heat Illness (Main)
• Environmental Main

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