LESSON 2 - FUNDAMENTALS OF FOREST FIRE CONTROL
2.6 Heat Transfer
Fire spreads by means of heat being transferred from one fuel to another or within the fuel itself. This is accomplished by the following - Radiation - Convection - Conduction
Radiation is the primary means by which fuels ahead of the fire are preheated. Radiated heat acts like light; it travels in straight lines. This is the kind of heat transfer you would sense if you were to stand close to a fire and feel your body warm up on the side close to the fire, but remain cold on the other side. When it strikes an object it may be absorbed, heating the object. It decreases in intensity, as does light, with increasing distance. Surface fires are mainly spread by radiated heat.
Convection is the transfer of heat by the movement of hot air and other heated gases. Hot air rises because it becomes less dense with increased heat, thereby causing it to rise. Crown fires are mainly spread by convection heat. Convection activity may be very vigorous and give rise to fire induced winds (pulled in from the sides to fill the void) and ember showers.
This is the kind of heat transfer you sense if you placed your hand above a flame.
Conduction is the transfer of heat within a fuel or from one fuel to another by direct contact. Most ground fires and sub-surface fires start and spread by this method. It is because of the transfer of heat by conduction that we sever roots when building a fire line. Tree roots act as conductors for fire/heat to travel.
This completes Lesson 2 - Fundamentals of Forest Fire Control