system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do embers stay burning for hours, even while buried beneath soot/ash?
gpt
The oxygen in the air is burning the fuel in the wood. Imagine the oxygen as a thirsty person, and the wood/charcoal/whatever as a glass of water. If the embers are completely open to the air, the oxygen can just drink it all up quickly. When the fuel is covered up with ashes and soot, it is more like trying to drink through a cocktail straw, as there is a much smaller path for the oxygen to get to the wood. So, the fuel takes longer to burn (and doesn't burn as hot)