The Scandinavian countries have in later years seen several severe wildfires and is expected to exhibit more severe fire danger. While direct flame spread has been an important topic in wildfire research, there is a need for development and to ensure that experimental methods are relevant for Scandinavian wildfire characteristics. To ensure relevant lab conditions for fire-resilient material development work, large lab-scale (2×4 meters) experiments were conducted on various fuels. Its fire behaviour (such as rate of spread, fireline intensity and flame length) was compared with ongoing wildfire field studies from ongoing field studies in boreal and hemiboreal Sweden. The lab fire experiments show good potential to mimic relevant natural wildfire conditions in the laboratory once a standard design fire exposure for fire resilient materials is developed.

This final report summarises the work carried out during the project SI2.825082 financed by the European Commission – DG GROW. Within this project a theoretical Round Robin with the aim to analyse how the initial assessment method is interpreted by different laboratories, and the first and second phase of the initial testing activities to investigate the fire source, the design of the combustion chamber and secondary opening have been carried out. The final step in the project was an experimental Round Robin where four façade systems were tested at three different laboratories using the assessment method document, resulting in 24 tests. Additional tests were added to the project with funding from industrial partners. The tests were used to determine a calibration scheme and suitable performance criteria for classification. Furthermore, a substantial work has been done to ensure that the project is communicated in a good way to all stakeholders and Member States representatives.The theoretical Round Robin was performed with 29 laboratories, all members of European Group of Organisations for Fire Testing, Inspection and Certification (EGOLF). Over 200 questions covering the whole assessment method were asked, and thereafter analysed. The results show clearly which parts of the assessment method needs to be improved and clarified, as well as some practical details regarding the test method that had to be addressed.The first phase of the initial testing program defined the requirements of the fuel source and the combustion chamber. A large quantity of wood, of two different wood species (spruce and pine), had been acquired and thereafter characterised by measurement of dimensions, weight and moisture content. Over 4000 sticks have thus been density graded. After the selection of sticks to the different wood cribs a series of tests have been performed, mainly in accordance with the original test plan. Some modifications to the test plan were made during the course of the experimental study e.g., tests with a crib platform with either a grated or a solid floor. Also, a theoretical study through numerical modelling has been made to study the impact of changes of the combustion chamber geometry on the heat exposure to the test specimen. The simulations showed only small deviations between the regular and the enlarged combustion chamber. The changes of the geometry of the combustion chamber for the large exposure test can be done according to the results from the experimental program, it is beneficial for two reasons: it would make the preparatory work when mounting the test specimen simpler and it would ensure that falling parts will not damage the wood crib during a test.Based on the results a proposal has been made on the characteristics of the fuel source and the geometry and design of the combustion chamber, to be used in the second phase.During the second phase of the initial testing activities large and medium-scale exposure testing was performed on full façade geometries. The testing program including three repeatability tests in addition to gather information on variation in volume flow of the fan in medium-scale exposure as well as effects of the modified combustion chamber and wind in large-scale. From the repeatability tests it was decided to keep a constant height of the wood crib in large-scale due to otherwise large variations in exposure to the façade. Furthermore, the wind effects on the façade temperatures were significant even with a moderate wind of 1-2 m/s. At the end of the second phase three tests in medium and three tests in large-scale were done to investigate the effect of a secondary opening. It was indicated that asymmetrically placed opening would be the most appropriate placement.A short test series on alternative fuel source for the large exposure test was also performed where a propane diffusion burner was used instead of wood cribs. It was shown that if the combustion chamber would be reduced in height similar exposure to the façade could be achieved using the propane burner. There are several benefits with this alternative fuel source such as decreased height, less cleaning, higher safety and therefore less costs associated to10testing. For the medium exposure test the alternative gas burner described in DIN 4102-20 might be an appropriate alternative fuel source for the wood crib. However, no further investigations were made in this project in this regard.An update of the assessment method was made to take into account the latest information such as the repeatability tests and the second phase of the testing program. These changes such as the placement of the wood crib and the secondary opening was used in the experimental Round Robin.In tandem to this work, two surveys on falling parts were performed to find out the needs of Member States (MS) and setting criteria to be used during the Round Robin. Furthermore, an inquiry on the capacities for indoor and outdoor testing of different testing laboratories connected with EGOLF was made and is reported here.The work on the experimental Round Robin was completed in March 2024 and presentations of the tests and specimens are discussed in this report, more detailed information is available in the comparative documents. These include comparisons between tests on the same type of façade system at the different laboratories. This enables inter-laboratory comparisons for each monitored quantity and position. The inert tests are used to determine suitable calibration schemes for the medium and the large-scale exposure method, whereas the remaining tests are used to determine the performance criteria. Here it should be noted that average temperature is a more stable assessment criterion than a peak temperature or above a certain temperature during a certain time interval. The consortium would like to stress that arranging this type of Round Robin exercise is a severe logistic challenge which requires extensive planning.The project has been communicated through different channels. The project web page is the main communication channel where all reports and other documentation is published (https://www.ri.se/en/what-we-do/projects/european-approach-to-assess-the-fire-performance-of-façades). In addition to the webpage a YouTube channel is available showing a few of the tests and recent seminars, see webpage for a link.A Comments Handling Document has been kept and it includes almost 1000 comments that have been received during the project. These comments were handled continuously and communicated through the above-mentioned web page.

How large are the global warming emissions from prescribed fires in the European boreal? This report addresses emissions of greenhouse gases during prescribed fires, which are done in Sweden for increased biodiversity. Focus is on CO2-emissions during the combustion. There are large instantaneous emissions to the atmosphere. However, the CO2-debt, i.e. the difference in atmospheric CO2 if the burning is conducted or not, decreases rapidly in the years following the burn as carbon is stored in soil and growing plants. The emissions from prescribed burning on protected land can be assessed using field observations of fuel loads, fuel consumption during the fire and post fire plant/litter accretion. The net change in atmospheric CO2 is thereafter calculated from these data sets for different time since fire. Instantaneous emissions are estimated, for a characteristic fuel type, at 14.4 tonnes CO2 per hectare. After only ten years 78 % of this is again fixed in the vegetation on the forest floor, and litter. The same number 20 years post fire is 90 % and at 50 years, 98 %.

Sample tests were conducted to obtain thermal and kinematic parameters for wood and high-density polyethylene (HDPE) that were used in a series of intermediate scale tunnel fire tests with and without water-based fire suppressions systems. The thermal properties were measured using Transient Plane Source (TPS) and Transient Line Source (TLS). The pyrolysis kinetics parameters were tested based on Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Different methods were used to obtain pyrolysis kinetics parameters. Different oxygen concentrations exposed to samples were tested and the results showed its significant influence in the charring process.

Increased risk of wildfires is often highlighted in media coverage of climate change in the Nordic countries. How an increased risk is reflected in the concerns and adaptive measures within the most likely affected communities is nevertheless not known. This study investigates concerns and adaptation to wildfires in a rural community in south-eastern Sweden. The comparatively dry study area has a history of frequent but often low-consequence wildfires and is projected to experience Sweden’s largest increase in severe fire weather towards 2100. Through narratives, this study elucidates potential wildfire concerns in this area and motivations behind adaptation measures. The narratives are compared to a physical causal network extracted from the literature on fires and their consequences in the region. Residents foresee an increased wildfire risk but do not consider it a threat to the future well-being of the community. Forest owners and homeowners express low commitment in preventive or adaptive measures. Instead, contrasting the reality of the twentieth century, the fire service is currently considered to be responsible for both preventing and suppressing fires. This attitude is attributed to the lack of severe implications from the generally well-managed fires in the region. Actions for prevention and adaptation seem triggered by media attention or experience from real high-consequence events occurring elsewhere, rather than local wildfire occurrence or climate change projections. © The Author(s) 2024.

Background: Directly after snowmelt, northern grasslands typically have highly flammable fuel-beds consisting of 100% grass litter. With green-up, the addition of high-moisture foliage leads to progressively decreasing fire hazard.

Aims: Our aim was to create a fire-danger index for northern grasslands that incorporated grass phenology.

Methods: We made use of 25 years of Swedish wildfire data and 56 experimental fires conducted during one full fire-season, merged with established models for moisture content and flame spread rates. Refined data on equilibrium moisture content of grass litter were obtained through laboratory tests.

Key results: The RING (Rate of spread In Northern Grasslands) model uses cumulative air temperature as a proxy for growing season progression. Three independent functions account for impact of wind, moisture content and the damping effect of live grass, respectively. The latter results in exponentially decaying rate of spread (ROS) with the progressing season. Following the field experiments, green grass proportion as low as 10–20% (live/dead dry-mass) resulted in model-ROS so reduced that the grassland fire season could effectively be considered over.

Conclusions: The model, calculated from standard meteorological data only, matches the experimental results and separately performed validation tests, as well as wildfire dispatch data.

Implications: RING has been used in Sweden since 2021 and is likely applicable to other northern regions as well.

Fire ignition probability is an essential component of most fire risk assessment frameworks. This study, framed within the H2020 project FirEUrisk, features a cohesive modelling approach in a set of representative regions (pilot sites; PS) in terms of fire activity across the European territory. These PS encompass different wildfire regimes in contrasting environmental settings: PS-1 Northern Europe, Kalmar Iän (South-East Sweden); PS-2 Central Europe, Southern Brandenburg and Eastern Saxony (Germany), North Bohemia (Czechia), and Lower Silesia (Poland); PS-3 Central Portugal; PS-4 Barcelona province (Spain); and PS-5 Attica region (Greece). Our main goal was to develop a common approach to model human-caused ignitions at a fine-grained spatial resolution (100 meters). For each pilot site we: (i) ascertain which factors influence ignition, hence, addressing potential differences in driving forces and, (ii) provide a spatial-explicit depiction of the patterns of ignition probability. For that propose, we fitted a Random Forest (RF) model in each PS from historical fire records (compiled by local fire agencies) and geospatial layers for land cover, accessibility, and population related factors. All models attained a high predictive accuracy, with AUCs that ranging from 0.69 (Northern Europe) to 0.89 (Attica Region). In turn, the most relevant explanatory variable was the population density that ranked most influential in four out of the five PS, followed by the fuel type, distance to roads, distance to the WUI, and percent cover of forest and wildlands. These findings are a valuable product to upscale future solutions at regional level (beyond NUTS3-type areas), conduct fire behavior modelling simulations, and enrich the science-based decisions which come from the forest and fire management agents at national and European level. © 2023 University of Split, FESB.

Post-flashover fires inherently lead to external fire plumes, constituting a hazard for rapid fire spread over façades. As multi-storey mass timber buildings with internal visible timber surfaces become more common, there are concerns that such buildings would produce larger external plumes and hazards (assuming all other parameters equal). The literature reveals only indications of this, and how the actual exposure relates to different test methods for assessment is unknown. Here we utilise a series of full-scale mass timber compartment tests to quantify the exposure to the external façade. An incombustible external façade is instrumented with gauges at positions corresponding to reference data from several different assessment methods. The results show that there is an increase in plume duration, height, and temperatures when increasing the areas of exposed timber, but that this increase is less for normal- to large-opening compartments, than was previously seen in small-opening compartments. Also, normal variations in external wind speed have a larger influence on plume heights than the effect of doubling exposed timber surfaces. Test methods used for regulatory compliance differ significantly not only in exposure but also in pass/fail criteria. The proposed European large exposure method and the BS8414 method exhibit exposures on par with the severe end of what could be expected from mass timber compartments, whereas methods like SP Fire 105 and Lepir II produce significantly less severe plumes. However, the safety level is always a combination of exposure and assessment criteria. This data can help justify assessment criteria from a performance perspective. © 2023 The Authors. 

Despite increasing concern over wildfires in Fennoscandia, there are essentially no studies on the survivability of buildings within the wildland-urban interface of this region. We make use of four recent large-scale fires in Sweden to elucidate which factors are important for survival, using multiple logistic regression analysis of data collected at the sites. We obtained data on 187 buildings within the fire perimeters, nearly all with wood paneling and tile- or sheet metal roofing. 35 % of the buildings were lost or badly damaged. Results indicate that most buildings were approached by relatively low-intensity fire and that ignition primarily occurred through direct flame contact. The most important factor for survivability was the presence of a maintained lawn. The second most important was that no flammable material was present close to the building façade. Further, fire intensity often decreased close to buildings due to a larger portion of deciduous trees around gardens than in the surrounding forest. These factors were more important than specific features of the building itself, reflecting that the majority of buildings have combustible wooden façades. Our results suggest that the greatest potential for increasing building safety in the Swedish WUI is to keep the area immediately surrounding the building (∼5 m) free from tree litter and other flammable material. Also, since fire intensities are generally low, buildings can in most cases be defended with simple tools without compromising personal safety.

Organization of successful wildfire prevention and suppression require detailed information on ignition causes, size distributions and relations to weather. From a large and highly detailed dataset of Swedish wildfire incidents (n = 124 000) we assess temporal, geographical and human-related patterns over a 25-year-period (1996–2020). We find strong positive correlations between population density and wildfire occurrence, primarily caused by a wide spectrum of human activities. However, fires >10 ha mostly occurred in sparsely populated regions and were more often ignited by lightning or heavy machinery. Further, large fires had a history of long response times and insufficient mop-up, in turn intimately linked to low population density. We detect no trend over the 25-year-period in either fire weather, number of ignitions or burned area, but a dramatic decline in wildfire caused by children's play as well as by springtime burning of dead grass, a traditional fire use in rural areas. Our results indicate that irrespective of climate change, societal changes such as rural depopulation and cultural shifts are imminently important for the future fire regime in this intensely managed part of the boreal, and may warrant more attention worldwide.