Invited review paper for the first issue of the journal IRECHE - International Review of Chemical Engineering - Rapid Communications.

Smouldering is the slow, low-temperature, flameless form of combustion of a condensed fuel. It poses safety and environmental hazards and allows novel technological application but its fundamentals remain mostly unknown to the scientific community. The terms filtering combustion, smoking problem, deep seated fires, hidden fires, peat or peatlands fires, lagging fires, low oxygen combustion, in-situ combustion, fireflood and underground gasification, all refer to smouldering combustion phenomena. This paper attempts to synthesize a comprehensive view of smouldering combustion bringing together contributions from diverse scientific disciplines. Smouldering is the leading cause of deaths in residential fires and a source of safety concerns in space and commercial flights. Smouldering wildfires destroy large amounts of biomass and cause great damage to the soil, contributing significantly to atmospheric pollutant and green house gas emissions. Subsurface fires in coal mines and seams burn for very long periods of time, making them the oldest continuously burning fires on Earth. Worthy of consideration are the novel environmental and energy technologies being developed based on the direct application of smouldering combustion. These include the remediation of contaminated soils, production of biochar for long term storage of carbon, enchanted oil extraction from reservoirs and gasification of coal seams. The prospect of new opportunities for science and engineering in smouldering combustion are noticeable, but a much larger international research effort is required to increase the number of multidisciplinary experimental, theoretical and field studies.