Ember

Embers from a barbecue.

Embers are the glowing, hot coals made of greatly heated wood, coal or other carbon based material that remain after, or sometimes precede a fire. Embers can glow very hot, nearly as hot and sometimes as hot as the fire which created them. They radiate a substantial amount of heat long after the fire has been extinguished, and if not taken care of properly can rekindle a fire that is thought to be completely extinguished and can pose a fire hazard to anyone who is not careful. In order to avoid the danger of accidentally spreading a fire, many campers pour cold water on the embers to cool them off.

They are often used for cooking, such as in charcoal barbecues, and are preferred over open flame when roasting marshmallows (traditionally called smores) on a campfire. This is because embers radiate a more constant form of heat, as opposed to an open fire which is constantly changing along with the heat it radiates.

An ember is usually formed when a fire has only partially burnt a piece of fuel, and there is still usable chemical energy in that piece of fuel. Often this happens because the usable chemical energy so deep into the center so that air (chemically O₂) does not reach it, therefore not causing combustion (Carbon-based fuel + O₂ --> CO₂ + H₂O + C + other chemicals involved). The reason that it continues to stay hot and does not lose its thermal energy quickly is because combustion is still happening at a miniature scale. The small yellow, orange and red lights often seen snaking throughout embers are actually combustion. There just is not enough combustion happening at one time to create a flame. By the time embers are completely 'burned through,' almost all of it is pure Carbon with loose physical bonds, which is why they crumble with the slightest touch. At that point they are normally called ashes.