Thermal Failure · WBGT
WBGT heat-stress index — the ACGIH work/rest cycle standard.
Heat kills through evaporative failure, not raw temperature. WBGT = 0.7·Tw + 0.2·Tg + 0.1·Td (outdoor) captures humidity (wet-bulb), radiant load (globe), and air temp (dry). Wet-bulb > 35°C = fundamental limit of human thermoregulation.
Part of: Environmental Stressors
How to use
- Enter wet-bulb, globe, and dry-bulb temps in °F or °C.
- Toggle direct-sun if outdoors.
- Read WBGT and the ACGIH status band (nominal / moderate / high / extreme / fatal-risk).
Examples
Before you act on the result
Health-related tools are educational planning aids. They can make a number or assumption visible, but they do not diagnose, treat, prescribe, or replace clinician guidance.
If the result points to risk, symptoms, medication questions, or urgent changes, use it as a note for a qualified professional rather than a final decision.
Next up
Frequently asked questions
› Why wet-bulb and not heat index? Troubleshooting
WBGT handles radiant and direct-sun load; heat index is dry + humidity only. WBGT is the ISO 7243 and ACGIH TLV standard.
› What happens at wet-bulb 35°C?
Evaporative cooling fails — skin can't shed heat faster than metabolism generates it. Fatal within hours regardless of hydration, shade, or fitness.
Tips & related reading
See the Environmental Stressors hub →Tips & how-tos
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