Study of the jump fire produced by the interaction of two oblique fire fronts. Part 1. Analytical model and validation with no-slope laboratory experiments

Abstract

When two fires approach each other, convective and radiative heat transfer processes are greatly enhanced. The interaction between two linear fire fronts making an angle θoi between them is of particular interest as it produces a very rapid advance of their intersection point with intense radiation and convection activity in the space between the fire lines. This fire is designated here as a ‘jump fire’ for when the value of θoi is small, the intersection point of the fire lines can reach unusually high rate of spread values that decrease afterwards in the course of time. A very simple analytical model based on the concept of energy concentration between the fire lines is proposed to explain this behaviour, which in large-scale fires can be of great concern to personnel and property safety. Experimental tests performed at laboratory scale on a horizontal fuel bed confirmed the basic assumptions of the model and provide a framework to extend the present analysis to more general conditions, namely to explain the behaviour of real fires. Given the rapid changes in fire behaviour, ‘jump fires’ can be considered as a form of extreme fire behaviour.

Defining Extreme Wildfire Events: Difficulties, Challenges, and Impacts

“…An increasing perimeter length requires more human and technological resources to control the fire and can affect the response capacity of suppression crews, which can be rapidly overwhelmed [114]. ROS can reach values of about 333 m/min [115] or even 450 m/min [116] and is considered extreme when it is ≥ 50 m/min [117]. ROS can also have major impacts on the safety of the evacuation process.…”

Experimental Research on Upslope Fire and Jump Fire

“…Besides upslope fires, the V-shape fire front is also concerned with another fire phenomenon called "jump fire", which is a new concept proposed by Viegas [12]. A jump fire denotes the phenomenon that two fire fronts (generally with a small separation angle) spread and meet each other, making up of a V-shape fire topology, and then merge to produce very high rates of spread because of high concentration of energy.…”

“…A jump fire denotes the phenomenon that two fire fronts (generally with a small separation angle) spread and meet each other, making up of a V-shape fire topology, and then merge to produce very high rates of spread because of high concentration of energy. Viegas [12] pointed out that the importance of jump fire lies in two aspects. Firstly, in some fire accidents two spreading fire lines were observed to intersect and merge, which led to a jump fire.…”

“…Although upslope fire and jump fire share the common features of V-shape fire fronts and high rates of spread of the intersection point between the fire fronts, they may differ from each other in physical mechanisms and behaviors. Basically, as indicated by Viegas [12], the generation of a jump fire is related to the interactions between the two fire lines that intersect with a relatively small angle between them, which lead to the merging of the fire lines and sharp increase of the displacement velocity of the intersection point.…”

Overview of Forest Fire Propagation Research

“…2), and consequently to very strong convection effects. A simple analytical model based on the accumulation of energy near D was proposed by Viegas et al [25] …”