Resurfacing of underground peat fire: smouldering transition to flaming wildfire on litter surface

Yichao Zhang; Yang Shu; Yunzhu Qin; Yuying Chen; Shaorun Lin; Xinyan Huang; Mei Zhou

doi:10.1071/WF23128

RESEARCH ARTICLE (Open Access)

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Resurfacing of underground peat fire: smouldering transition to flaming wildfire on litter surface

Yichao Zhang ^A ^B , Yang Shu ^B , Yunzhu Qin

^A , Yuying Chen ^A , Shaorun Lin

^C ^* , Xinyan Huang

^A ^* and Mei Zhou ^B

+ Author Affiliations

- Author Affiliations

^A Research Centre for Fire Safety Engineering, Department of Building Environment and Energy Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong.

^B Forestry College, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia, China.

^C Department of Mechanical Engineering, University of California, Berkeley, CA, USA.

^* Correspondence to: shaorun.lin@berkeley.edu, xy.huang@polyu.edu.hk

International Journal of Wildland Fire 33, WF23128 https://doi.org/10.1071/WF23128

Submitted: 4 August 2023 Accepted: 8 January 2024 Published: 5 February 2024

© 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

Smouldering wildfires in peatlands are one of the largest and longest-lasting fire phenomena on Earth, but it is unclear whether such underground peat fires can resurface to the ground and ignite a flame on the litter layer.

Methods

This work conducted a laboratory experiment by putting a 5-cm thick litter layer (banyan tree leaves with a density of 27–53 kg/m³) onto a 10-cm thick peat sample (moisture content of 10–100%).

Key results and conclusions

Tests confirmed that a smouldering peat fire, ignited at the bottom, can propagate upwards and resurface to ignite a flaming wildfire on the surface litter layer. The propensity of litter to be flaming ignited decreased with increasing peat moisture content and litter layer density. We found the threshold of such surface flaming as a function of temperature and temperature increase rate at the interface between peat and litter. Finally, large field experiments successfully reproduced and validated the laboratory observations.

Implications

This work reveals an important wildfire ignition phenomenon that has received little attention but may cause new spot fires, accelerate fire progression and exacerbate its hazards.

Keywords: flaming ignition, hot spot, litter layer, peat fire, re-emerging wildfire, smouldering to flaming transition, upward peat fire, wildland fire.

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