| 1. |
- Vermina Lundström, Frida, et al.
(författare)
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Analysis of extinction and sustained ignition
- 2019
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Ingår i: Fire safety journal. - : Elsevier BV. - 0379-7112 .- 1873-7226. ; 105, s. 51-61
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Tidskriftsartikel (refereegranskat)abstract
- The limiting conditions for sustained burning of materials are studied experimentally using gas burners. Small pool fire configurations are examined to determine the mass flux for a sustained surface diffusion flame (fire point) and the subsequent extinction limit of that flame. The burner results are compared to material data for sustained ignition, and are found to be lower. Material reported values of a critical mass flux are disparate, and burner data show that the critical mass flux can range from about 1 to 50 g/m2s. Previous studies have indicated the results depend on the convective heat transfer coefficient and the heat of combustion of the gases, but until this work no study has been presented to systematically show these dependencies. Three porous gas burners of diameters 25, 50 and 100 mm were used with fuel gases including methane, propane, isobutene, and ethylene mixed with nitrogen to precisely change the mixture heat of combustion. Diffusion flame theory based on a critical flame temperature at extinction is used to explain and correlate data for both limits. It was found that there is no statistical difference between the sustained ignition and extinction limits. A correlation for the critical mass flux is produced with heat of combustion and fuel diameter as sole dependent variables for all the fuels except methane. The results show that no burning is possible below a heat of combustion of 3–4 kJ/g. This is consistent with the European classification system for non-combustibility where the corresponding limit is set at 2 kJ/g.
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| 2. |
- Andersson, Petra, et al.
(författare)
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Riskreducerande åtgärder för dödsbränder i bostäder
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Thisreport summarizes the work conducted within the project ”Analysis of physicaldeterminants and technical measures in support of the zero vision” financed bythe Civil Contingency Authority (MSB) in Sweden. The work aims to find measuresto prevent and reduce the number of fatalities in fires in residentialbuildings in a Sweden, a list of such measures is provided in the end of thereport. The list is based on work conducted in several small sub-projects, ashort summary of these is also provided in the report.
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| 3. |
- Brandon, Daniel, et al.
(författare)
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SAFITS - Statistical Analysis of Fires in Timber Structures
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Due to changes of regulations and product development among other things, the number of multi-storey buildings of timber frame or heavy timber construction has increased consistently in the last two decades. The use of a combustible materials in the structure and the relatively short history with such buildings, has led to insurance related questions regarding risks of property loss. Studies of damages in real fire incidents, where a fair comparison between the fire performance of modern multi-storey timber buildings is made, were lacking. In this study damage data of fire incidents from the USA, Canada, Sweden, New Zealand were found and analyzed. Using different methods the extent of fire damage or the financial damage was compared for fires in multistorey buildings of timber construction types and fires in multistorey buildings of other construction types. For each database a qualitative assessment of the reliability and the fairness of the comparison was made. Also, a comparison, for which only a limited number of fire incidents was available, was made between damages caused in sprinklered fires and damages caused in non-sprinklered fires. In addition to the comparative study also qualitative analysis of 33 high damage fire incidents in multistorey timber buildings was made. The goal of this assessment was to identify the most important details to prevent high damage fires.
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| 4. |
- Lundström, Frida Vermina, et al.
(författare)
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Challenges in determining critical mass flux for ignition
- 2015
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Ingår i: Fire and Materials 2015 - 14th International Conference and Exhibition, Proceedings. ; , s. 198-209
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Konferensbidrag (refereegranskat)abstract
- Traditionally in fire modelling, a solid fuel has been assumed to ignite when the solids surface reaches a specific temperature or when the heat flux upon the solid reaches a critical level. Although these approaches of determining ignition for the condensed phase are practical, ignoring the gas phase conditions may lead to incorrect assumptions regarding material safety. A more 'physical' explanation for piloted ignition cases may be that ignition occurs when the fuel-air-mixture around the location of a pilot has reached the lower flammability limit. In this study, challenges of retrieving a critical mass flux for piloted ignition is theoretically evaluated. Then a simple model is presented, by which the critical mass flux (analogous to the piloted fire point) of a solid fuel's effluents may be obtained. Finally, the model is validated against literature data. Initial results indicate that the model predicts ignition reasonably well, however further validation needs to be done, both when it comes to predicting ignition for different types of materials and for other environments.
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| 5. |
- Lundström, Frida Vermina, et al.
(författare)
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Study of ignition and extinction of small-scale fires in experiments with an emulating gas burner
- 2017
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Ingår i: Fire Safety Journal. - : Elsevier BV. - 0379-7112. ; 87, s. 18-24
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study is to explore mechanisms for ignition and extinction for condensed-phase fuels via the use of a gas-fueled burner. Flames were generated with a porous 25 mm circular burner using mixtures of methane and propane with nitrogen. The procedure was to specify a set of mass fluxes of nitrogen-fuel mixture that corresponded to the flash- fire- and extinction points and for the minimum mass flux where steady burning was achieved. The results show an increase in the critical mass flux with a decreased heat of combustion. The data fall into two regimes depending on the mixture flow rate; one buoyancy-driven (Fr<1) and one induced by momentum jet forces. The buoyancy-driven regime is geometrically consistent with the definitions of flash and fire points under natural convection conditions. The results for the momentum regime align reasonably with existing stagnant layer theory. Extinction theory is also suggested to give approximate results for the fire point. This argument is based on similar flame geometries for fire point and extinction and theoretical reasoning. An anchor point is proposed as the end point of ignition. Produced anchor point data result in a flammability diagram, below which quasi-steady burning occurs.
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| 6. |
- Nilson, Finn, et al.
(författare)
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Framgångsfaktorer vid bostadsbränder - sammanfattningsrapport
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The report briefly summarizes the findings about success factors for residential fires in Sweden. Three main approaches have been used to investigate residential fires where the consequences have been small, i.e. the fire has been handled by the residents themselves or has self-extinguished. Factors facilitating these events have been identified using insurance statistics, national accident questionnaires and rescue services incident reports in combination with interviews of rescue services personnel. From a sociodemographic point of view no typical residential group can be identified as being more protected or being exposed to significant higher risk. Based on the information from the rescue services interviews an early detection of a fire in combination with an ability to respond seem to be factors indicating success.
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| 7. |
- Sjöström, Johan, et al.
(författare)
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Skogsbränder orsakade av skogsmaskiner
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Several large wildfires in Sweden are caused by forestry machinery in operation, but there is no overview or characterization of machine-caused fires. Combining dispatch data, weather, fire danger and interviews with forestry entrepreneurs we gain a deeper understanding of spatial/temporal/weather distributions of these fires as well as their characteristics and underlying mechanisms. The average annual number of machine-caused ignitions in Sweden is estimated to 330-480 (2.0±0.4 ignitions per 1000 ha clear-felled land) of which 34.5 lead to fire-fighter dispatch. These constitute 2.2% of all forest fires and 40% of area burnt. Soil scarification causes most ignitions and the main mechanism is likely high-inertia contact between discs and large stones, causing sparks igniting dry humus/moss. This counters reports suggesting that such metal fragments cannot fulfil ignition requirements. We found a strong spatial relationship between forestry machinery ignitions and the abundance of large stones, represented by a boulder-index generated from 13500 nation-wide site inventories. Further, 75% of the dispatches occurred on days with relative humidity <45%, Duff Moisture Code >26 and Fire Weather Index >12. 75% of the total area burned when Fire Weather Index >20. Cancelling operations in stony terrain during high-risk weather situations can largely avoid the problem.
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| 8. |
- Sjöström, Johan, et al.
(författare)
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Wildfire ignition from forestry machines in boreal Sweden
- 2019
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Ingår i: International journal of wildland fire. - : CSIRO. - 1049-8001 .- 1448-5516. ; 28:9, s. 666-677
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Tidskriftsartikel (refereegranskat)abstract
- Several large Swedish wildfires during recent decades were caused by forestry machinery in operation, fires for which there is still no characterisation. We combined 18 years of data on dispatches, weather and fire danger and interviewed forestry workers to understand the spatial, temporal and weather distributions of these fires, and their underlying mechanisms. We estimate the average annual number of ignitions from forestry machinery in Sweden at 330-480 (2.0 ± 0.4 ignitions per 1000 ha clear-felling) of which 34.5 led to firefighter dispatches, constituting 2.2% of all forest fire dispatches and 40% of area burnt. Soil scarification causes the most ignitions and the main mechanism is likely high-inertia contact between discs and large stones, causing sparks igniting dry humus or moss, countering reports suggesting that such metal fragments cannot fulfil ignition requirements. We found a spatial relationship between forestry machine ignitions and abundance of large stones, represented by a Boulder Index generated from a nationwide dataset. Further, 75% of the dispatches occurred on days with relative humidity <45%, Duff Moisture Code (Canadian system) >26 and Fire Weather Index >12. 75% of the area burned when Fire Weather Index was >20. Results suggest machine-caused forest fires can be largely avoided by cancelling operations in stony terrain during high-risk weather.
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| 9. |
- Vermina Lundström, Frida, et al.
(författare)
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A review on prediction models for full-scale fire behaviour of building products
- 2017
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Ingår i: Fire and Materials. - : Wiley. - 0308-0501. ; 41:3, s. 225-244
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Tidskriftsartikel (refereegranskat)abstract
- This study aims to give an overview over different reaction-to-fire prediction models developed over the last decades by finding similarities and differences between models, as well as identifying their robustness in scaling. The models have been divided into four categories - empirical, thermal, polynomial and comprehensive - depending on how pyrolysis is modelled. Empirical models extrapolate bench-scale test results to larger scales. These models are pertinent to applications that they have been validated for, but surfacic parameters used may not be scalable. In thermal models, pyrolysis is represented by heat transfer rates. The models are feasible for materials with high activation energies and where little pyrolysis occur before ignition. Polynomial models are empirical models that also take the environment into account. The validity of scaling is yet to be established. The comprehensive methodology includes chemical kinetics in the condensed phase. It has the potential to be used for any application; however, many parameters are needed. This increases the degrees of freedom versus data available for the description of the problem. Consequently, possible errors are introduced, and uncertainty is increased. A comprehensive multi-scale methodology is a way forward, where many steps of validation are possible.
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| 10. |
- Vermina Lundström, Frida, et al.
(författare)
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Faktorer som påverkar en bostadsbrands storlek – analys av försäkringsbolagens data
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Every year, the insurance sector reports 23 000 fire incidents in Sweden. Of these, the fire rescue service are called into 6 000. Since there is little knowledge on the fires that the fire rescue service is not involved in, incident data from insurance companies has been analyzed.One limitation to the results in this report is that the insurance sector’s definition of fire is broad; e.g. short-circuit is regarded a fire incident.Still, the data complies with the statistics from the fire rescue service: Kitchen fires and fire in electric equipment are the most common sources of fire in residential buildings.The cost (property damage) of a fire is also presented. It is seen that the most common fires sources commonly lead to a relatively low economical loss.
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