What is the purpose of a heat stress index and name one commonly used index?

• A. To assess heat-related risk; WBGT is commonly used.
• B. To measure humidity; Dew Point is commonly used.
• C. To measure air velocity; ACH is commonly used.
• D. To measure surface roughness; Ra is commonly used.

Answer: (A)

A heat stress index translates environmental conditions into a single number that reflects how hot it feels to the human body and the risk of heat-related illness. It combines factors that affect heat gain and loss—ambient temperature, humidity, radiant heat from surroundings, and air movement—so you can judge when cooling measures, rest breaks, hydration, or other protections are needed.

A commonly used example is the Wet-Bulb Globe Temperature (WBGT). It uses three measurements—wet-bulb temperature (capturing evaporative cooling and humidity), globe temperature (capturing radiant heat), and dry-bulb air temperature—to produce a single value that indicates heat stress risk. This makes it practical for setting work-rest schedules and safety guidelines in hot environments.

Humidity metrics like dew point tell how humid it is, but they don’t by themselves account for radiant heat or airflow. Similarly, measuring air velocity or ventilation (ACH) or surface roughness doesn’t capture the overall heat stress risk the body experiences.