Propagation probability and spread rates of self-sustained smouldering fires under controlled moisture content and bulk density conditions

Prat‐Guitart, Nuria; Rein, Guillermo; Hadden, Rory M.; Belcher, Claire M.; Yearsley, Jonathan M.

doi:10.1071/wf15103

Cited by 63 publications

(48 citation statements)

References 45 publications

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“…Compared with the dried peat (MC ¼ 10%), the spread rate for MC ¼ 35 and 70% increases ,80 and 150% respectively. This result goes against our intuition and is opposite to the previous finding in the horizontal spread near the free surface for the same peat (same type, density and MC), where the spread rate decreased with increasing MC (Huang et al 2016;Prat-Guitart et al 2016). There are two possible reasons: (1) the water in the porous peat matrix increases the overall thermal conductivity in the drying zone, which facilitates the heat transfer from the upstream oxidation zone, and (2) the reduction of fuel density (r p ) due to the natural expansion of peat sample after the water absorption (see Fig.…”

Section: Resultscontrasting

confidence: 99%

“…Specifically, the spread rate is found to be in the range from 0.5 to 2 cm h À1 , which agrees with the measurement in the natural peat fire (Usup et al 2014). Also, it is in the same order of the horizontal spread rate (S h , cm h À1 ) of the same peat (Huang et al 2016;Prat-Guitart et al 2016), but slightly smaller (see Fig. 4c).…”

Section: Resultsmentioning

confidence: 73%

“…2b). Compared with the naturally sourced peat, it was readily available in large quantities, has relatively homogeneous properties and constant composition, and has been used in a series of past experiments (Belcher et al 2010;Hadden et al 2013;Huang et al 2016;Prat-Guitart et al 2016). After the oven-drying process, this moss peat has a bulk density of 135 AE 5 kg m À3 in its natural state and a low mineral content (IC ,2%).…”

Section: Methodsmentioning

confidence: 99%

“…As (1) the vertical dimension was clearly larger than the cross-section dimension and (2) the smouldering spread is extremely slow, the whole downward spread may be approximated as a 1-D spread phenomenon, similar to those in Benscoter et al 2011 andZaccone et al 2014). This 1-D dominated downward spread of smouldering peat fire without the wind is different from other multi-dimensional smouldering spread over small and shallow peat samples (Hadden et al 2013;Huang et al 2016;Prat-Guitart et al 2016;Yang et al 2016).…”

Section: Introductionmentioning

confidence: 96%

“…The DOB and critical MC for extinction ðMC Ã ex Þ at the vertical downward (or indepth) spread of peat fires have been investigated by various experiments (Benscoter et al 2011;Watts 2012;Davies et al 2013;Zaccone et al 2014) and numerical simulations Rein 2015, 2016a;Yang et al 2016). Recently, laboratory experiments on the horizontal fire spread over a shallow peat sample showed that the spread rate decreased with MC but increased with the forward wind speed (Huang et al 2016;Prat-Guitart et al 2016). However, He et al (2014) found that the downward smouldering spread rate over the piled biomass powder was not sensitive to MC from 3 to 21%.…”

Section: Introductionmentioning

confidence: 99%

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Downward spread of smouldering peat fire: the role of moisture, density and oxygen supply

Huang

Rein

2017

Int. J. Wildland Fire

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115

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Abstract. Smouldering fires in peatland are different from the flames in wildland fires. Smouldering peat fire is slow, low-temperature and more persistent, releasing large amounts of smoke into the atmosphere. In this work, we experimentally and computationally investigate the vertical downward spread of smouldering fire in a column of 30 cm-tall moss peat under variable moisture content (MC) and bulk density. The measured downward spread rate decreases with depth and wet bulk density, and is ,1 cm h À1 equivalent to a carbon emission flux of 200 tonnes day À1 ha À1 . We observe that downward spread increases as MC increases substantially at least inside the range from 10 to 70%, which is not intuitive and goes against the trend observed for the horizontal spread in the same peat. We also conduct one-dimensional computational simulations to successfully reproduce the experimental observations. The analysis shows that the spread rate increases with MC and decreases with density because smouldering spread is controlled by the oxygen supply. The volume of the porous peat expands when absorbing water, which reduces the density of organic matter and decreases the heat release rate. This shows that the widely assumed conclusion that the spread rate of wildfire decreases with MC is not universal when applied to smouldering fires.

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Section: Resultscontrasting

confidence: 99%

Section: Resultsmentioning

confidence: 73%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Downward spread of smouldering peat fire: the role of moisture, density and oxygen supply

Huang

Rein

2017

Int. J. Wildland Fire

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115

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Fine‐scale distribution of moisture in the surface of a degraded blanket bog and its effects on the potential spread of smouldering fire

et al. 2017

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During rain‐free periods, the water table in peatlands falls and the moisture content (MC) of top 10 cm, including the moss layer, depends upon the hydrophysical properties and the responses of the local composition of species to water deficit. Thus, the ecosystem becomes vulnerable to surface peat fires. The spread of such fires is often irregular; however, there is little understanding of how the fine‐scale variation of peat MC can affect the spread of smouldering fire. We analyse the fine‐scale distribution of surface MC from a degraded blanket bog (i.e., horizontal intervals of 10 cm), thus indirectly analysing the effect of fine‐scale MC distribution on peat fire spread. We determine the relationship of vegetation and microtopography to the spatial distribution of near surface MC and the moisture gradient around patches of dry peat (less than 250% MC, moisture content in a dry mass basis). We found that the MC of the surface peat was distributed in clusters with dry patches (less than 250% MC) averaging 40 ± 15 cm in size. The MC gradient surrounding dry patches was 10 ± 7% MC∙cm−1. A mixed‐effects model showed that dry patches were associated with lawns (of feather moss or Sphagnum) and hummocks of feather moss. Our model showed that wet patches were associated with both hummocks and hollows of Sphagnum. Therefore, the characterization of the surface MC in a fine‐scale is critical if we are to understand the spread of fires in peatlands.

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Hydrologic‐based modelling of burn depth potentials in degraded peat soils

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McLaughlin

Stewart

et al. 2023

Hydrological Processes

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Peatland drainage may degrade system resilience to high intensity, soil-consuming fires. Peat soil fires are unique in that they can smoulder vertically through the soil column, with a multitude of consequences including large carbon emissions, altered hydrology, and dramatic shifts in vegetation communities. In this work we developed and verified a new method to model peat burn depths with readily available water level and peat hydraulic property data at the Great Dismal Swamp National Wildlife Refuge (VA and NC, USA). To model peat burn depths across 11 sites in the Great Dismal Swamp National Wildlife Refuge we combined water table time series data and soil moisture release curves, developed at multiple depths, with moisture-to-ignition thresholds. A subset of the results from this empirical modelling approach of peat burn depth severity were compared against those made using a mechanistic model of soil moisture, HYDRUS 1-D. By comparing modelled burn depth potentials between these two approaches for a range of peats, we confirmed that our simpler, water table-based approach had similar performance to HYDRUS 1-D in drained and degraded peats, like those found in the Great Dismal Swamp National Wildlife Refuge. A comparative analysis of modelled burn depths across our study site found that water table position and peat water holding capacity were the key governing controls on burn depth potential.Our findings suggest that drainage weakens both short-and long-term controls on peat burn depths by reducing soil moisture and by decreasing peat water holding capacity. This new approach offers land managers with an additional tool for assessing risk while offering insight into the drivers of peatland wildfire severity.

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Propagation probability and spread rates of self-sustained smouldering fires under controlled moisture content and bulk density conditions

Cited by 63 publications

References 45 publications

Downward spread of smouldering peat fire: the role of moisture, density and oxygen supply

Downward spread of smouldering peat fire: the role of moisture, density and oxygen supply

Fine‐scale distribution of moisture in the surface of a degraded blanket bog and its effects on the potential spread of smouldering fire

Hydrologic‐based modelling of burn depth potentials in degraded peat soils

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