Which humidity level stops evaporation entirely, potentially causing dangerous rise in body temperature?

Which humidity level stops evaporation entirely, potentially causing dangerous rise in body temperature?

• A. Humidity level that impairs evaporation
• B. Humidity level that reduces evaporation
• C. Humidity level slows evaporation
• D. Humidity level of 75% stops evaporation entirely

Answer: (D)

Evaporative cooling depends on a vapor-pressure gradient between the skin and the surrounding air. Sweat on the skin evaporates by moving into the air; this process carries heat away from the body. When the air is humid, the gradient shrinks because the air already contains more water vapor, so evaporation slows and cooling becomes less efficient. If the air were completely saturated with water vapor (relative humidity of 100%), it can’t accept any more moisture, and evaporation from the skin effectively stops. Without this evaporation-based cooling, the body’s ability to shed heat during exertion or in hot environments is severely impaired, which can lead to a dangerous rise in core temperature.

A humidity level of 75% is very high and will impede cooling by slowing evaporation, but it does not stop it entirely. The key point is that evaporation halts only at full saturation, not at 75%.