WBGT Heat Stress Calculator

OSHANIOSH
Heat Stress Assessment
Enter temperature measurements and work conditions to calculate WBGT and assess heat stress risk.

Temperature Measurements

Natural wet bulb temperature measured with a thermometer wrapped in wet wick exposed to natural air movement (°C)

Temperature measured with a 150mm matte black sphere thermometer (°C)

Environment Type

Select whether the work area has direct solar exposure

Work Conditions

Walking, moderate lifting, driving heavy vehicles

60 min work / 0 min rest per hour

Are workers acclimatized to heat? (5-7 days of gradual exposure)

Clothing Adjustment

Add adjustment for protective clothing (WBGT increases with heavier PPE)

Frequently Asked Questions

Common questions about this calculator

WBGT (Wet Bulb Globe Temperature) is a heat stress index that combines temperature, humidity, radiant heat, and wind to assess heat risk. It's used by OSHA, NIOSH, and military to set work/rest schedules and prevent heat illness.

Outdoors: WBGT = 0.7×Twb + 0.2×Tg + 0.1×Ta (wet bulb, globe, air temp). Indoors: WBGT = 0.7×Twb + 0.3×Tg. Wet bulb accounts for humidity, globe for radiant heat. The calculator handles both environments.

ACGIH TLVs for continuous work: Light work ≤30°C, Moderate ≤26.7°C, Heavy ≤25°C. Above limits, require work/rest cycles. NIOSH REL values are lower for unacclimatized workers. The calculator shows applicable limits.

Acclimatized workers can tolerate 2-3°C higher WBGT than unacclimatized. Full acclimatization takes 7-14 days of gradual exposure. Lost after 1-2 weeks away from heat. The calculator adjusts limits based on acclimatization status.

Use a 6-inch (150mm) black globe thermometer placed at chest height in the work area. Let it equilibrate for 20-25 minutes. Without a globe, the calculator can estimate from air temp and solar radiation.

Based on WBGT vs. TLV: Continuous work below limit, 75% work/25% rest at limit, 50%/50% above limit, 25%/75% well above. Rest means sitting in shade with water. The calculator recommends specific schedules.