The Cannon rear coal form is located within the coal section. The fire coals only appear in appliances that do not have a closed burner section. They serve two functions. The first is to allow heat to be emitted from the fire. The second function is safety. They are designed to slot together in a specific way that optimises combustion. If the coals or pebbles are assembled incorrectly, harmful gases could escape from the fire due to incomplete combustion.