Which index is commonly used to assess heat stress and which variables does it include?

• A. PTT; pulse rate, temperature, humidity, air velocity.
• B. SPL; sound pressure level, humidity, wind.
• C. WBGT; dry bulb temperature, wet bulb temperature, globe temperature, humidity, wind, and clothing.
• D. HCI; heat conduction index, immersion, radiation, airflow.

Answer: (C)

WBGT, the Wet Bulb Globe Temperature, is the index most commonly used to assess heat stress because it blends the main environmental factors that drive how hot it feels and how the body loses heat. It relies on three measurements: dry-bulb temperature (the surrounding air temperature), wet-bulb temperature (air cooled by evaporation, which reflects humidity and the potential for evaporative cooling), and globe temperature (heat from radiant sources captured by a black globe). Together, these capture temperature, humidity/evaporative demand, radiant heat, and to some extent air movement. In practice, clothing effects are accounted for with a clothing adjustment factor, further tailoring the index to how someone’s apparel influences heat stress. This combination makes WBGT more representative of real heat stress risk than single-parameter measures, which is why it’s widely used for occupational heat exposure limits and work-rest guidelines. The other options describe measures that do not reflect the combined environmental drivers of heat stress (for example, sound levels or unrelated concepts).