The application of water, or water mixed with suppressants, to combat wildfires is one of the most common firefighting methods but is rarely studied for smouldering peat wildfire, which is the largest type of fire worldwide in term of fuel consumption. We performed experiments by spraying suppressant to the top of a burning peat sample inside a reactor. A plant-based wetting agent suppressant was mixed with water at three concentrations: 0% (pure water), 1% (low concentration), and 5% (high concentration), and delivered with varying flowrates. The results showed that suppression time decreased non-linearly with flow rate. The average suppression time for the low-concentration solution was 39% lower than with just water, while the high-concentration solution reduced suppression time by 26%. The volume of fluid that contributes to the suppression of peat in our experiments is fairly constant at 5.7 AE 2.1 L kg À1 peat despite changes in flow rate and suppressant concentration. This constant volume suggests that suppression time is the duration needed to flood the peat layer and that the suppressant acts thermally and not chemically. The results provide a better understanding of the suppression mechanism of peat fires and can improve firefighting and mitigation strategies.

Peat fires smoulder for long periods (weeks to months) and releasing large amount of ancient carbon that have been stored for millennia in the organic soils. Recent wildfires in Arctic regions have burned unprecedented swaths of land, demonstrating a detrimental change in the arctic fire regime and highlighting the vulnerability of these biomes to climate change. This work aims to experimentally study Arctic peat fires in the lab scale by using an experimental rig with adjustable air temperature and bottom boundary of the peat fire which imitate the condition of permafrost in the Arctic. The initial temperature of the peat sample varied from -13 to 18°C, and the moisture content (MC) was varied from 50 to 120% in dry-mass basis. The experimental results show that smouldering can be sustained with soil temperatures below the freezing point of water. The range of condition temperature in this study was found to insignificantly affect spread rate but have profound effect on the depth of burn, increasing by up to 66% as bottom boundary decreased from 21 to -7°C. We found that the critical moisture content of ignition under cold condition in this work is between 110 and 120% (dry-mass basis), and is lower than the literature in room temperature (160%). At high moisture content (≥100% MC), smouldering was weakly spreading under air temperature of ~12°C, initial peat temperature of -11°C, and bottom boundary of -7°C. However, spread rate significantly increased as the air and bottom boundary temperatures were increased to 22°C, demonstrating overwintering fires which often found in the Arctic when peat fires were considered to be extinguished only to resurface when warmer season arrives. This study is the first experimental work on smouldering Arctic wildfires with findings that can improve our understanding on the effect of cold temperatures on the smouldering dynamics of peat fires, and presents a novel methodology to investigate Arctic fires at laboratory scale.

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Peat wildfires can burn over large areas of peatland, releasing ancient carbon and toxic gases into the atmosphere over prolonged periods. These emissions cause haze episodes of pollution and accelerate climate change. Peat wildfires are characterised by smouldering -the flameless, most persistent type of combustion. Mitigation strategies are needed in arctic, boreal, and tropical areas but are hindered by incomplete scientific understanding of smouldering. Here, we present GAMBUT, the largest and longest to-date field experiment of peat wildfires, conducted in a degraded peatland of Sumatra. Temperature, emission and spread of peat fire were continuously measured over 4-10 days and nights, and three major rainfalls. Measurements of temperature in the soil provide field experimental evidence of lethal fire severity to the biological system of the peat up to 30 cm depth. We report that the temperature of the deep smouldering is ~13% hotter than shallow layer during daytime. During night-time, both deep and shallow smouldering had the same level of temperature. The experiment was terminated by suppression with water. Comparison of rainfall with suppression confirms the existence of a critical water column height below which extinction is not possible. GAMBUT provides a unique understanding of peat wildfires at field conditions that can contribute to mitigation strategies.