Chimney effect induced by smoldering fire in a U-shaped porous channel: A governing mechanism of the persistent underground coal fires

Zeyang Song, Xinyan Huang, Claudia Kuenzer, Hongqing Zhu, Juncheng Jiang, Xuhai Pan, Xiaoxing Zhong

Research output: Journal article publicationJournal articleAcademic researchpeer-review

21 Citations (Scopus)


This paper presents underground coal fires (UCF) induced natural ventilation through a U-shaped porous channel. Height of the U-shaped channel (the fire depth) is one of key elements determining the accessibility of air supply to UCF. Conventionally, we acknowledge that under the external wind driving force, air supply to underground space should decay with increasing the fire depth. However, under the thermal buoyancy force induced by UCF, responses of air supply and UCF to the fire depth are uncertain. Herein we propose a 1/20-scale experimental framework to measure air velocity, and to quantify the burning rate, the fire spread rate and the burning temperature of UCF at different fire depths (H = 1.6–4.6 m) with variable aperture sizes (Φ = 1–4 cm). A one-dimensional model correlating the air velocity with the fire depth is validated and then extrapolates laboratory-scale free channels into field-scale (H = 100 m) percolation channels. We find the ‘chimney effect’ – air supply driven by the buoyant smoke of UCF is unexpectedly enhanced with increasing the fire depth; the enhanced air supply due to the chimney effect facilitates burning of coal. The chimney effect, serving as a self-sustaining mechanism of air supply to UCF, is a significant governing mechanism for persistent UCF burning for hundreds or even thousands of years.

Original languageEnglish
Pages (from-to)136-147
Number of pages12
JournalProcess Safety and Environmental Protection
Publication statusPublished - Apr 2020


  • Natural ventilation
  • Stack effect
  • Subsurface fire
  • Thermal buoyancy

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Chemical Engineering(all)
  • Safety, Risk, Reliability and Quality

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