Fire whirls induced by a line fire on a windward slope: a laboratory-scale study

Kuibin Zhou; Yifan Wang; Albert Simeoni; Ruixing Dong

doi:10.1071/WF23048

RESEARCH ARTICLE (Open Access)

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Fire whirls induced by a line fire on a windward slope: a laboratory-scale study

Kuibin Zhou ^A ^B ^* , Yifan Wang ^A , Albert Simeoni ^B and Ruixing Dong ^A

+ Author Affiliations

- Author Affiliations

^A College of Safety Science and Engineering, Nanjing Tech University, Nanjing, Jiangsu, 211816, China.

^B Department of Fire Protection Engineering, Worcester Polytechnic Institute, Worcester, MA 01609, USA.

^* Correspondence to: kbzhou@njtech.edu.cn

International Journal of Wildland Fire 33, WF23048 https://doi.org/10.1071/WF23048

Submitted: 11 April 2023 Accepted: 23 November 2023 Published: 12 December 2023

© 2024 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of IAWF. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Background

Fire whirls are often reported to occur in wildland fires and can induce serious difficulties in firefighting by abruptly modifying fire behaviour, exposing firefighters and even causing casualties.

Aims

The aim of this study was to examine the formation of fire whirls on a windward slope.

Methods

Straight and V-shaped heated wires and burners were used to emulate fire spread fronts of various fire intensities. Different slope angles and ambient wind speeds were considered, to observe the formation and behaviour of fire whirls.

Key results

A fire whirl appeared over a straight-line fire in the presence of wind, and a couple of counter-rotating fire whirls appeared over the two flanks of a V-shaped line fire.

Conclusions

Two interaction regimes were experimentally observed and theoretically explained for the interaction of two fire whirls. We found that an effective wind speed instead of the local wind speed in sloped terrains can quantify the critical condition for the formation of fire whirls over line fires of different burning intensities.

Implication

A critical effective wind speed correlation that couples slope angle, burning intensity and radiative fraction of a line fire can predict fire whirl risk in wildland fire fighting.

Keywords: ambient wind, fire intensity, fire line, fire whirl, firefighting, line fire, slope steepness, vortex flow, V-shaped fire, windward slope.

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