Transitional flame-spread and fuel-regression behaviors under the change of concurrent wind

On the occurrence of an environmental wind, the steady-state flame spread will go through a transitional process to a new steady state of the concurrent flame spread. However, such a transition between two steady states was rarely studied, despite that it often happens to many fire events. This paper presents an experimental study on the transitional flame-spread behavior over the horizontal PMMA plate by applying different concurrent airflows from the still air. The flame spread rate at the pyrolysis leading edge and the regression rate in the fuel rear end were studied during this transition. Such a transition could be divided into three stages based on both the length of pyrolysis and the fuel regression rate, (1) increasing to maximum, (2) dropping from peak, and (3) reaching a new steady-state. The concurrent wind velocity showed different influences on the flame spread rate and the fuel-rear regression rate during the transition. This work provides novel experimental data on the transitional behavior of wind-assisted flame spread, which helps evaluate the fire hazard under the sudden change of environmental conditions.