Final answer:
Firewalkers don't burn their feet because of the Leidenfrost effect which creates a protective vapor layer and because the coals have poor thermal conductivity, limiting heat transfer.
Step-by-step explanation:
Firewalkers are able to walk on hot coals without burning their feet due to two key reasons. First, the Leidenfrost effect, where a layer of moisture on the skin can create a protective barrier that reduces heat transfer. When water on the foot's surface evaporates, it cools the skin, much like sweat cools the body. Second, wood and charcoal have poor thermal conductivity, meaning that heat does not transfer quickly to the feet which limits the amount of time the skin is exposed to extreme temperatures.
Firewalkers are able to walk barefoot on red-hot coals without burning their wetted feet due to two main reasons: the insulating properties of water and the low thermal conductivity of the callused skin on the bottom of their feet.
Water as an insulator: When the firewalkers wet their feet, a thin layer of water forms on the surface of their skin. Water has a high specific heat capacity, meaning it can absorb a significant amount of heat without significantly increasing in temperature. This layer of water acts as an insulator, preventing the heat from the red-hot coals from quickly transferring to their skin.
Low thermal conductivity of callused skin: The bottom of a firewalker's foot is typically covered in a thick layer of callus, which has a lower thermal conductivity than normal skin. This means that it is not as effective at conducting heat, further reducing the amount of heat transferred from the coals to their feet.