How does PPE prevent evaporative cooling?

• A. The liner reflects evaporative heat
• B. The vapor barrier limits evaporation of sweat
• C. The thermal barrier prevents heat transfer
• D. Perspiration is absorbed in the layers

Answer: (B)

Evaporative cooling depends on sweat evaporating from the skin, which takes energy from the body and cools it. A vapor barrier inside PPE blocks water vapor from escaping from the wearer’s skin or undergarments to the outside environment. Because the sweat vapor can’t leave the suit, evaporation is limited, so less latent heat is removed, and you feel warmer. This is why PPE with a vapor barrier is effective at preventing liquid penetration but can hinder the body's natural cooling through sweating. The other ideas describe general heat transfer or moisture staying in the layers, but they don’t specifically prevent sweat from evaporating in the same way a vapor barrier does.