Effects of spatial heterogeneity in moisture content on the horizontal spread of peat fires

Abstract

The gravimetric moisture content of peat is the main factor limiting the ignition and spread propagation of smouldering fires. Our aim is to use controlled laboratory experiments to better understand how the spread of smouldering fires is influenced in natural landscape conditions where the moisture content of the top peat layer is not homogeneous. In this paper, we study for the first time the spread of peat fires across a spatial matrix of two moisture contents (dry/wet) in the laboratory. The experiments were undertaken using an open-top insulated box (22×18×6cm) filled with milled peat. The peat was ignited at one side of the box initiating smouldering and horizontal spread. Measurements of the peak temperature inside the peat, fire duration and longwave thermal radiation from the burning samples revealed important local changes of the smouldering behaviour in response to sharp gradients in moisture content. Both, peak temperatures and radiation in wetter peat (after the moisture gradient) were sensitive to the drier moisture condition (preceding the moisture gradient). Drier peat conditions before the moisture gradient led to higher temperatures and higher radiation flux from the fire during the first 6cm of horizontal spread into a wet peat patch. The total spread distance into a wet peat patch was affected by the moisture content gradient. We predicted that in most peat moisture gradients of relevance to natural ecosystems the fire self-extinguishes within the first 10cm of horizontal spread into a wet peat patch. Spread distances of more than 10cm are limited to wet peat patches below 160% moisture content (mass of water per mass of dry peat). We found that spatial gradients of moisture content have important local effects on the horizontal spread and should be considered in field and modelling studies.

Investigation of smoldering combustion propagation of dried peat

“…Meanwhile the peak temperatures for Papua peat were about 611 with smoldering propagation rate of 4.8 cm/h. These findings are in accordance with previous experimental data of about 600 [13], 500 -600 [7], 500 -700 [14], 400 -600 [15], and about 400 [16]. Likewise, the results for smoldering propagation rate were also in line with previous experiments.…”

“…The mass of ash for each type of peats were 5.8 gram and 4.4 gram. These particular values were lower than results from Rein and Prat's experiments, with the mass of ash for each experiments 38 gram/hour [7] and 1.7 gram/min (dry peat) and 0.9 gram/min (other moisture treatments) [16]. The percentage of mass loss indicates that organic material of the condensed "peat" sample were relatively the same with other experiments, 80% [4] and > 90% [7].…”

“…Likewise, the results for smoldering propagation rate were also in line with previous experiments. Wein's experiment discovered a propagation rate of 4.2 cm/h for Australia peat and 3 -12 cm/h for Canada peat [17], 2.8 -6.0 for numerous moisture content arrangements [16]. Whereas for other experimental results, the propagation rates are relatively higher or lower, 1 -3 cm/h [7,13,14], 3.6 cm/h [3], 3.83 cm/h [18], 0.5 -10 cm/h for Russian peat [17], 9.8 and 10 cm/h [16,19].…”

Potential production of palm oil-based foaming agent as fire extinguisher of peatlands in Indonesia: Literature review

“…In general, the foam used to fight the fire is easily evaporate because surface temperatures of fire is higher than foam temperature [19,43] so it is required a lot of foam volume. The evaporation of the foam is caused by bubbles rupture, film layer thinning and coalescent that cause foam collapse.…”

Experimental study of the influence of ignition source position on the parameters of peat fire propagation

“…A promising method for studying the propagation of peat fires is the thermography method. There are the experimental works which estimate the characteristics of a horizontal peat fire front [8,19], as well as the depth of the peat combustion front [20] with the use of this method.…”