Wildfires are uncontrolled combustion events occurring in the natural environment (forest, grassland, or peatland). The frequency and size of these fires are expected to increase globally due to changes in climate, land use, and population movements, posing a significant threat to people, property, resources, and the environment. Wildfires can be broadly divided into two types: smouldering (heterogeneous combustion) and flaming (homogeneous combustion). Both are important in wildfires, and despite being fundamentally different, one can lead to the other. The smouldering-to-flaming (StF) transition is a quick initiation of homogeneous gas-phase ignition preceded by smouldering combustion, and is considered a threat because the following sudden increase in spread rate, power, and hazard. StF transition needs sufficient oxygen supply, heat generation, and pyrolysis gases. The unpredictable nature of the StF transition, both temporally and spatially, poses a challenge in wildfire prevention and mitigation. For example, a flaming fire may rekindle through the StF transition of an undetected smouldering fire or glowing embers. The current understanding of the mechanisms leading to the transition is poor and mostly limited to experiments with samples smaller than 1.2 m. Broadly, the literature has identified the two variables that govern this transition, i.e., oxygen supply and heat flux. Wind has competing effects by increasing the oxygen supply, but simultaneously increasing cooling. The permeability of a fuel and its ability to remain consolidated during burning has also been found to influence the transition. Permeability controls oxygen penetration into the fuel, and consolidation allows the formation of internal pores where StF can take place. Considering the high complexity of the StF transition problem, more studies are needed on different types of fuel, especially on wildland fuels because most studied materials are synthetic polymers. This paper synthesises the research, presents the various StF transition characteristics already in the literature, and identifies specific topics in need of further research.

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.

Fire in a typical car park is capable to induce large Heat Release Rate. The heat release rate in car park can be ranged from 500 kW to 20 MW depends on the ventilation condition of the car - park and the car itself. When fire occurs in poor ventilated car, i.e. the window is closed, fire will immediately burn out. Otherwise, fire will rapidly spreads and consume adjacent car. This condition can result in wide spread of fire involving all of the available car in the parking lot considering the availability of ventilation in underground car - park which strongly affect the fire and smoke spread. In this paper, a typical large underground car - park is being considered by varying the aspect ratio of the parking lot shape with constant floor to ceiling height. The effect of horizontal ventilation system and its thrust direction on the spread of smoke, its flow pattern, and overall CO distribution will be covered. In addition, the impact of additional building structure, basement aspect ratio, and ceiling beam will be discussed by considering it effect on smoke flow pattern and extraction effectiveness. Furthermore, based on the simulation which had been carried out the dilution of smoke by the air from the horizontal ventilation system is significantly increasing the CO concentration at 2 m height as it disturbed the smoke concentration stratification.

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