Heat Stress is defined as the net load to which a worker may be exposed to from the combined contributions of metabolic heat, environmental factors and clothing requirements.

• A. The net load to which a worker may be exposed to from the combined contributions of metabolic heat, environmental factors and clothing requirements.
• B. The body’s attempt to maintain a stable internal temperature.
• C. Hydration level during work.
• D. The rate at which heat is lost through evaporation.

Answer: (A)

Heat stress is the total heat burden a worker has to cope with, coming from three sources: the metabolic heat the body generates during activity, environmental factors that add or remove heat (like air temperature, humidity, radiant heat, and air movement), and the insulating effect of clothing that can trap heat and reduce cooling. When these sources combine, they create the net heat load the body must dissipate to stay within safe temperatures. The statement that describes this combined net load—encompassing metabolic heat, environmental factors, and clothing requirements—matches the concept of heat stress precisely.

What this isn’t is a description of thermoregulation (the body's process of maintaining a stable internal temperature), nor a measure of hydration status, nor a description of a single cooling mechanism like evaporation rate. Those relate to related aspects of heat exposure, but not the definition of heat stress itself.