What is the standard WBGT formula used for outdoor work?

• A. WBGT = 0.7 × T_nwb + 0.2 × T_g + 0.1 × T_d (where T_nwb is natural wet-bulb, T_g is globe, T_d is dry-bulb temperature).
• B. WBGT = 0.5 × T_nwb + 0.3 × T_g + 0.2 × T_d
• C. WBGT = 0.3 × T_nwb + 0.3 × T_g + 0.4 × T_d
• D. WBGT = 0.7 × T_nwb + 0.2 × T_d + 0.1 × T_g

Answer: (A)

The main idea here is how outdoor heat stress is quantified by WBGT, which blends different temperature readings to reflect evaporative cooling, radiant heat, and ambient air temperature.

The standard outdoor formula uses WBGT = 0.7 × T_nwb + 0.2 × T_g + 0.1 × T_d, where T_nwb is the natural wet-bulb temperature, T_g is the globe temperature, and T_d is the dry-bulb (ambient air) temperature. The natural wet-bulb temperature carries the most weight because it integrates humidity and the body’s ability to cool itself through evaporation; when humidity is high, evaporation is limited and heat stress increases, which this term captures with the largest coefficient. The globe temperature accounts for radiant heat from the sun and surrounding surfaces, hence the moderate 0.2 weight. The dry-bulb temperature reflects the surrounding air temperature but doesn’t directly represent humidity or radiant heat, so it has the smallest influence with a 0.1 weight.

This arrangement best mirrors how workers actually experience heat outdoors, where humidity and solar radiation have strong effects on perceived heat stress. The other sets of weights either swap the roles of the radiant and air components or change the proportions, which do not align with how WBGT is defined for outdoor conditions.