Many dramatic consequences of wildfires, particularly in terms of lives lost, are due to extreme fire behavior, with sudden changes in fire spread, in what have been termed as blow-up, eruptive or flashover fires. Descriptions of such extreme events are common between survivors of wildfires that use terms as lakes of fire, blanket of flames, or sudden explosions. These descriptions were common in the witnesses of the Pedrógão Grande wildfire of June 2017 which was well documented in videos recorded during the spread of the fire.

In spite of the unquestionable importance of understanding these phenomena, it is clear that current models of fire spread are not able to explain adequately these sudden changes in behavior. However, after such events in different parts of the world as in eucalypt forests of Australia or pine forest of Corsica, scientific explanations have been proposed. As a consequence, there is now a solid theory suggesting that flammable gases generated from heated vegetation, in particular Volatile Organic Compounds (VOCs) common in Mediterranean plants, or products from incomplete combustion in the wildfire front may, under some topographic and wind conditions, accumulate in locations where, after the arrival of the ignition source, they rapidly burst in flames as in explosions.

These flashover fires are a common feature in fires in houses where flammable gases in a confined environment easily concentrate above the Lower Flammability Limit and, given enough oxygen and ignition source, create explosive situations.

In the project EXTREME we propose to evaluate the conditions for those extreme events to occur based on the analysis of different components of the problem:

a) the release of flammable gases as VOCs by leaves of some of the main Portuguese tree species (Pinus pinaster, Eucalyptus globulus, Quercus suber and Quercus sp.) when subject to different temperatures and of flammable combustion products when subject to combustion with different oxygen supply;

b) the possible concentrations of flammable gases within the volume of a forest stand given the amount and distribution of leaves in the forest and the species considered;

c) the distribution of VOCs in the atmosphere in forest regions evaluated by remote sensing techniques; and

d) the integration of the previous knowledge in a Decision Support System that may assist silviculture decisions to influence forest composition and structure and to assist wildfire operations to enhance safety of firefighters and other people involved. A process-based model will be the basis for that integration.

A special emphasis will be given to the dissemination of the project results including a final workshop with the community of forest and fire managers that will have to consider these processes when make the decisions affecting the forests and the fire operations to avoid the conditions that allow the occurrence of these extreme events or to minimize their consequences.