Evaporative cooling becomes impaired beginning at what relative humidity level?

Evaporative cooling becomes impaired beginning at what relative humidity level?

• A. 65%
• B. 60%
• C. 75%
• D. 80%

Answer: (A)

Evaporative cooling relies on sweat evaporating from the skin to transfer heat to the air. As relative humidity increases, the air’s capacity to absorb more moisture decreases, shrinking the vapor pressure gradient between skin and air and slowing evaporation. This cooling impairment begins around 60–65% relative humidity, with 65% matching the given option. At much higher humidity, such as 75–80%, evaporative cooling is far more limited, making it harder for the body to dissipate heat during exercise.

Evaporative cooling relies on sweat evaporating from the skin to transfer heat to the air. As relative humidity increases, the air’s capacity to absorb more moisture decreases, shrinking the vapor pressure gradient between skin and air and slowing evaporation. This cooling impairment begins around 60–65% relative humidity, with 65% matching the given option. At much higher humidity, such as 75–80%, evaporative cooling is far more limited, making it harder for the body to dissipate heat during exercise.