A diver's body heat is lost through conduction (primarily) at a rate of approximately ____ times more rapidly than in air.

• A. 25
• B. 5
• C. 10
• D. 50

Answer: (A)

Heat transfer by conduction depends on how well the surrounding medium conducts heat. Water conducts heat far more efficiently than air, so heat moves from the diver’s body into the surrounding water much faster. Using typical values for thermal conductivity, water is about 0.6 W/m·K while air is about 0.024 W/m·K, giving a ratio near 25. That means heat loss through conduction is roughly twenty-five times faster in water than in air, which is why immersion in cold water chills the body so quickly and why insulation (like wetsuits) helps reduce that rapid transfer.