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

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Contents Vol 21(7)

doi:10.1071/WF10155

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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

Domingos X. Viegas ^A ^B ^C, Jorge R. Raposo ^A, David A. Davim ^A and Carlos G. Rossa ^A

^A ADAI/LAETA, Associação para o Desenvolvimento da Aerodinâmica Industrial, Rua Pedro Hispano 12, 3030-289 Coimbra, Portugal.
^B Department of Mechanical Engineering, University of Coimbra, Rua Luís Reis dos Santos, 3030-788, Coimbra, Portugal.
^C Corresponding author. Email: xavier.viegas@dem.uc.pt

International Journal of Wildland Fire 21(7) 843-856 http://dx.doi.org/10.1071/WF10155
Submitted: 31 December 2010 Accepted: 15 February 2012 Published: 18 July 2012





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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 θ_oi 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 θ_oi 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.

Additional keywords: converging fronts, fire behaviour, fire modelling.

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