Growth Free Burning Stage

Immediately after ignition, a fire plume forms above fuel that is burning expanding above the burning fuel. As it expands it starts to draw in air from the surrounding environment into the column. Initially the fire has a growth that resembles that of an unconfined fire. This growth is a function of the fuel burning.

Due to the confining effect of the ceiling and walls of the space occupied, the fire plume growth is affected. The initial effect results from the entrapped air, which is cooler, compared to the hot gases produced by the fire. This air brings about a cooling effect on the fire resulting in temperature reduction. The amount of air entrapped is determined by the location of the fuel package in respect to the compartment walls as a result affecting the magnitude of cooling that occurs. Less air is entrapped in situations where we have fuel packages near walls leading to very high plume temperatures. This has a considerable effect on the temperature of the developing hot-gas layer over the fire. With time the hot gases rise and start spreading to the compartment walls resulting in an increase in the depth of the gas layer. The change in temperature of the compartment is a function of the amount air entrapped, the total heat being conducted in the walls and ceiling and the position of the fuel package. It has been demonstrated through research that there is a consistent decrease in gas temperature with increase in distance from the centre of the plume. This growth stages are under the influence of the fuel. The overall temperature inside the compartment and of the gas layer at the level of the ceiling increases as the fire grows and grows.