WBGT (Occupational Heat Index)
Calculate the WBGT (wet bulb globe temperature) for indoor environments without solar load, WBGT = 0.7·t_nw + 0.3·t_g, from the natural wet-bulb temperature t_nw and the globe temperature t_g (°C). The result, in °C, is the heat stress index used to assess heat exposure: compared with tolerance limits according to the activity's metabolic rate, it sets the allowed work-rest regime. For environments with solar load, the dry-bulb temperature is also included. Enter the natural wet-bulb and globe temperatures.
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WBGT (heat stress index)
The WBGT (Wet Bulb Globe Temperature, known in Brazil as IBUTG) is the official index for assessing heat exposure at work, since it rolls into a single number the factors that drive heat strain: temperature, humidity (which limits sweat evaporation) and radiant heat (from furnaces, flames, the sun). For indoor settings, or outdoor ones with no solar load, the formula is WBGT = 0.7·t_nwb + 0.3·t_g, where t_nwb is the natural wet bulb temperature (a thermometer with a wetted wick exposed to natural air movement — it captures the effect of humidity) and t_g is the globe temperature (a thermometer inside a 15 cm black sphere — it captures radiant heat). The weights (70% and 30%) reflect that humidity is the more critical factor. For settings with solar load (open air, under the sun), the dry bulb temperature is added in, with weights 0.7/0.2/0.1. The result, in °C, is compared against the tolerance limits in NR-15, Annex 3 (the Brazilian occupational standard for heat exposure), which depend on the metabolic rate of the activity (light, moderate or heavy work): the heavier the effort, the lower the tolerable WBGT. When the WBGT exceeds the limit, the standard requires a work-rest regime (alternating spells of labor with breaks in a cool place) to head off heat strain and its consequences — from fatigue and cramps to exhaustion and heat stroke. Enter the natural wet bulb and globe temperatures.
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