The initial development of the fire is a product of the ignition source and the fuel present. The fire's growth results both from flamespread along the initial item and from flamespread from one item to the next. Heat transfer from the flame raises the temperature of the adjacent unburned fuel and promotes the further spread of the fire. Under favorable conditions, a self-sustaining chain reaction occurs. The nature of the enclosure in which the fire occurs will determine the further development of the fire. Ventilation will intensify the fire. Temperature increases which occur through the reradiation proces can lead to flashover, when items not in direct contact with the original flames suddenly burst into flames. The combustion process varies according to whether the fuel is solid, liquid, or gas. Fires usually receive oxygen, which combines with the fuel in the combustion process, from the surrounding air. Mixtures of fuel gas and air will burn only if their composition rests within certain limits. Smoke, the visible product of a fire, serves also as a warning of the presence of toxic gases. Two references are listed.