The main difference that glowing fires have from flaming fires is the absence of a flame. However, combustion is still undergoing on the surface of the fuel . Charcoal and coal fire are very common examples of glowing fires. Glowing fires are sustained when there is sufficient convection draft to retain the heat of the combustion. There is a tendency of flaming fires to smolder due to a lack of oxygen. This smoldering fire is, in fact, a glowing fire which can rekindle back into a flaming fire if there is a fresh supply of oxygen. One of the dangers of glowing fires is the production of carbon monoxide due to the deficiency of combustion in the face of a low oxygen supply and an excess of hot carbon. Another danger of glowing fires is the risk of it rekindling into a destructive fire after the fire is presumably put out. Seeking out such fires are the primary motives for firefighters during postfire cleanup or overhaul. Smoldering fires have also been responsible for starting fires when there seems to be no obvious sources for the ignition.