Wood is a poor heat conductor whether it is cold or hot, even in the form of smoldering, red-hot coals. Yes, you can safely walk across a bed of red-hot wooden coals (but don't!). Not much heat is conducted into your feet if you step quickly. Walking on red-hot iron coals would be a bad idea, because heat is easily conducted to your feet and you will suffer a bad burn. This is discussed on page 303.