How long will it take exposed skin to experience frostbite at -20 degrees Fahrenheit?

• A. 30 minutes
• B. One hour
• C. Two hours
• D. Four hours

Answer: (B)

Frostbite happens when exposed skin loses heat fast enough that the tissue begins to freeze. At very cold air temperatures like -20°F (-29°C), the rate of heat loss from unprotected skin is high, so even short exposures can risk freezing. Under typical dry conditions with minimal wind, around an hour of exposure is a reasonable estimate for the onset of frostbite on exposed skin. If wind is stronger or the skin is wet, frostbite can occur much sooner, while good clothing and dry protection extend the safe exposure time. With that in mind, about one hour is the best estimate for the onset under standard conditions.