Spontaneous ignition of soils: a multi-step reaction scheme to simulate self-heating ignition of smouldering peat fires

Abstract

As organic porous soil, peat is prone to self-heating ignition, a type of spontaneous initiation of fire that can take place at ambient temperatures without an external source. Despite the urgency to tackle peat fires, the understanding of the self-heating ignition of peat is insufficient. In this study, a computational model that integrates the mechanisms of heat transfer, mass transfer and chemistry is incorporated with a three-step reaction scheme that includes drying, biological reaction and oxidative oxidation to simulate the self-heating ignition of smouldering peat. The model is first validated against 13 laboratory-scale experiments from literature. For critical ignition temperature (Tig), the model gives accurate predictions for all experiments with a maximum error of 5°C. The validated model is then upscaled to predict Tig for field-size peat soil layers and compared with the predictions using a one-step scheme. The three-step scheme is shown to give more reliable predictions of Tig than the one-step scheme. According to the simulation results, for a 1.5-m-deep peat layer, self-heating ignition can occur at an average ambient temperature above 40°C. This is the first time that a multi-step scheme is used to simulate the self-heating ignition of peat, aiming to help in the prevention and mitigation of these wildfires.

Peat Soil Burning in the Mezzano Lowland (Po Plain, Italy): Triggering Mechanisms and Environmental Consequences

“…This evidence suggests self‐combustion of the organic‐rich soils. Similar processes have been described in the literature, especially in dry and warm conditions (Restuccia et al., 2017), and are explained as the result of multiple reaction steps including drying, biological activity, and oxidation, that are necessary to trigger the the spontaneous ignition of peat‐soils (Yuan et al., 2021).…”

“…The hypothesis is based on the fact that peat smoldering in the area is spatially associated to localized sectors characterized by high CH 4 seepage (with fluxes up to 120 g m −2 day −1 , according to Cremonini et al., 2008). Soil heating occurs at depth where there is the transition between anoxic and oxic conditions with concomitant methanotrophic bacteria activity that promotes temperature well exceeding 40°C (Capaccioni et al., 2015), which is considered a thermal condition necessary for self‐heating propensity (Yuan et al., 2021).…”

“…10.1029/2021GH000444 temperature well exceeding 40°C (Capaccioni et al, 2015), which is considered a thermal condition necessary for self-heating propensity (Yuan et al, 2021).…”

Rate-induced tipping to metastable Zombie fires

“…First, to strengthen our hypothesis, it would be interesting to build on the excellent agreement with the medium-complexity PDE model in figure 5 and extend the conceptual ODE model in different directions. For example, include terms describing peat soil ignition processes at higher temperatures [69]. This would allow investigation of existence of additional (quasi-)thresholds for the onset of flames.…”

KAPAS II: simulation of peatland wildfires with daily variations of peat moisture content

“…Research on smouldering wildfires at the field scale is limited (Purnomo et al 2021;Widyastuti et al 2021;Yuan et al 2021). The complexity and spatiotemporal extents of peatland wildfires prevent state-of-the-art wildfire models from properly simulating these phenomena.…”