Det sker en snabb teknikutveckling i den elektriska miljön i byggnader, framförallt i våra bostäder. Ett exempel är lokal produktion av el, där solcellsinstallationer blir alltmer populära. Sådan elproduktion medför även förändringar i övriga delar av byggnaders elektriska infrastruktur, såsom DC-nät och i vissa fall energilagring i batterisystem. Utvecklingen sker till stor del som ett svar på behovet av mer hållbara lösningar, ur ett växthuseffektperspektiv, för vår elförsörjning, och förstärks bland annat av statligt stöd och ökad tillgänglighet på marknaden.Ny elektrisk teknologi kan leda till ökad brandrisk och denna förstudie har haft som mål att undersöka denna problematik. Metoden har varit workshops med intressenter och experter inom området, intervjuer, samt litteraturstudier.Av de studerade områdena förefaller solcellsanläggningar skapa störst utmaningar i framtiden om inget görs. Detta beror dels på bristfälligt regelverk men även på att dessa system är distribuerade i byggnaderna med flera delar som kan orsaka brand och att delar är exponerade för utomhusklimat vilket får stora konsekvenser vad gäller uppkomst av fel.Brandsäkerheten i samhället har sett ur ett långt tidsperspektiv väsentligt förbättrats. Detta har huvudsakligen drivits fram med hjälp av ett förbättrat regelverk, som ofta inkluderat förbättrade provnings- och kvalificeringsmetoder. En generell observation i detta projekt är att regelverket inte hinner utvecklas i samma takt som tekniken. Detta är en ofta återkommande utmaning inom brandsäkerhet, men gäller speciellt för de teknikområden som behandlas i denna rapport där utvecklingen går mycket snabbt, och de ingående komponenterna nästan uteslutande har stor inneboende brandpotential. Rapporten konstaterar att för att skapa ett relevant regelverk behövs tillämpad forskning, så kallad prenormativ forskning, inom prioriterade områden för att besvara de frågor som ställs vid formulerandet av nya regler och standarder. Exempel på områden som bör prioriteras är 1) komplettering av det än så länge magra statistiska underlaget för bränder i solcellsinstallationer med olycksutredningar, och studier av redan befintliga olycksutredningar, 2) studier av branddynamiken i solcellsinstallationer, såväl byggnadsapplicerade som integrerade, och såväl tak- som fasadmonterade sådana, 3) studier av ljusbågars uppkomst och hur dessa kan undvikas, alternativt hur det kan undvikas att de ger upphov till bränder, 4) skapa underlag för säker installation av batterilager, samt 5) kvalitetssäkring av så kallade second-life batterier, dvs. begagnade batterier, som används i batterilager.
Radiative heat transfer to a solid is a key mechanism in fire dynamics, and in-depth absorption is especially of importance for translucent fuels. The sample-heater interaction for radiative heat transfer is experimentally investigated in this study with two different heaters (electric resistance and tungsten lamp) using clear PolyMethylMethAcrylate (PMMA) samples from two different formulations (Plexiglass and Lucite). First, the significant effects of the heater type and operating temperature on the radiative heat transfer are revealed with broadband measurements of transmittance on samples of different thicknesses. Then, the attenuation coefficient in Beer-Lambert's law has been calculated from detailed spectral measurements over the full wavelength range encountered in real fires. The measurements present large spectral heterogeneity. These experimental results and calculation of in-depth absorption are used to explain the reason behind the apparent variation of the fuel absorbance with the sample thickness observed in past studies. The measurement of the spectral intensity emitted by the heaters verifies that the common assumption of blackbody behavior is correct for the electric resistance, whereas the tungsten lamp does not even behave as a greybody. This investigation proofs the necessity of a multi-band radiation model to calculate accurately the fire radiative heat transfer which affects directly the in-depth temperature profiles and hence the pyrolysis process for translucent fuel.
The radiation emission of the heating coil of a Cone Calorimeter and the one of the halogen lamp of a Fire Propagation Apparatus have been studied experimentally for varying power settings. These are two standard apparatuses used for fire calorimetry. The objective is to characterize and compare the radiative flux spectrum received by a fuel sample during pyrolysis experiments. The deviation from the standard assumption of black or gray emission is discussed. It is observed that the emission of the heating coil can be approximated well to an ideal blackbody, especially in the infrared range. On the contrary, the halogen lamp emission is more complex, non gray, with an important contribution in the visible and in the near infrared ranges. The flux received by a sample exposed to these emitters is predicted using ray tracing simulations. This shows that the irradiation flux and spectrum from the cone can be accurately calculated if the coil temperature is known. The non Lambertian irradiation flux from the lamp is modeled with a combination of diffuse and collimated intensities, representing the direct emission from the lamp itself and the reflection by the mirror at the rear side. For both emitters, the irradiation is confirmed to be approximately uniform over the surface of a sample 5 cm large (maximum deviation of ±2% on the incident flux). The uniformity decreases for larger samples, but the ratio of the flux at the center to average flux is still 1.04 for standard 10 cm × 10 cm samples under the cone. For illustration purposes, the influence of the spectral characteristics of the emitter is studied in the case of a sample of PMMA, a non gray translucent medium. Using recently published measurements of PMMA absorptivity, the absorbed flux by a 3 cm thick sample is predicted. In the case of an incident flux of 20 kW/m2, the calculated average absorptivity of the sample is 0.91 under the cone, while it is 0.32 under the FPA lamp. These calculations involve absorption data of a virgin sample at room temperature and consequently the numerical results only hold for the initial instants of irradiation. However, the very large differences in radiative behavior show that important discrepancies in the pyrolysis behavior are expected between the two emitters. This might have consequences for fire testing and inter comparisons of flammability results worth further investigation.
This paper presents a recently developed method meant to act as a tool for objectively assessing and comparing the performance of automatic fire suppression systems. This methodology specifies requirements and procedures for evaluating the efficiency and performance of automatic fire suppression systems permanently installed in the engine compartments of buses and coaches. The testing is done according to SP method 4912 and carried out in a test enclosure where the fire performance of different suppression systems can be objectively assessed in a well-defined way. The test methodology includes a battery of fire tests simulating different engine loads, air flows and fire scenarios. Every tested system is rated according to its performance. The test method also includes testing of re-ignition due to hot surface ignition of liquid fuels.
Scheimpflug lidar is a compact alternative to traditional lidar setups. With Scheimpflug lidar it is possible to make continuous range-resolved measurements. In this study we investigate the feasibility of a Scheimpflug lidar instrument for remote sensing in pool flames, which are characterized by strong particle scattering, large temperature gradients, and substantial fluctuations in particle distribution due to turbulence. An extinction coefficient can be extracted using the information about the transmitted laser power and the spatial extent of the flame. The transmitted laser power is manifested by the intensity of the ‘echo’ from a hard-target termination of the beam located behind the flame, while the information of the spatial extent of the flame along the laser beam is provided by the range-resolved scattering signal. Measurements were performed in heptane and diesel flames, respectively. © 2023 The Author(s).
One of five Knowledge and Innovation Communities (KICs), was launched in Europe in 2014 and has its focus on exploration, extraction, mineral processing, metallurgy, recycling and material substitution of raw materials. To reach the vision, where the European Union’s industrial strength is based on a cost-efficient, secure, sustainable supply and use of raw materials, a new generation of skilled people entering industry, universities and research needs to be developed. Today’s technical MSc graduates in raw materials and especially primary resources (i.e. exploration, extraction, mining and mineral processing and metallurgy) best suits large companies where they often act as specialists and experts. For small to medium enterprises as well as for our future engineers other skills than technical are necessary. As a part of the KIC Raw Materials, the education project “The implementation of CDIO in raw material programmes” started in 2016. The project focuses, during 2016-2017, on (WP1) faculty- and (WP2) pilot case development. There are no academic institutes in Europe that have yet applied CDIO for primary resource related MSc programmes. This paper describes an education project within the KIC Raw material and presents key outputs with implementing CDIO in mining and metallurgy related programmes.
This study provides an analysis on the fire safety of passengers and the fire protection of coaches and buses. A brief review of major bus fire incidents, an overview of current regulations in Europe, and their limitations are presented. The study finds that the current small-scale fire test methods described in UN ECE Reg No. 118 need to be replaced by test methods that can assess the reaction to fire of materials when exposed to ignition sources of varying sizes. To address these shortcomings, the study proposed an expert recommendation to update the material fire safety requirements and testing for buses. Additional measures are proposed, derived from objectives and strategies applied in other transport sectors, and can be tested through existing European and international standards, which are widely used by several industries. These measures aim to extend the time with tenable conditions for a safe evacuation in case of fire, reduce the degree of damage to buses, reduce the risk for fast and excessive thermal exposure on modern energy carriers needed for a more sustainable transport sector. © 2023 The Authors.
Radiation is one of the two main heat transfer processes in transporting energy from flames to a surface. The other process is convection and was not considered in this report. The spectral absorptivity of 72 products was measured in the wavelength region 0.3-20 mm. This wavelength region contains virtually all radiation energy from a fire. Based on the measurements, and on the theory for radiative heat transfer, the effective absorptivity for fire induced heat radiation for the different products were calculated. These typically lies in the range 0.75-0.95. It was also found that the effective absorptivity varies significantly with the temperature of the heat source. The reason for this is that the spectrum of the emitted radiation from a heat source, such as a fire, changes with temperature. This has limited effect on the heating of a surface. The dependence of the effective absorptivity on heat source temperature is important when the absorptivity is used as input for calculations of ignition temperature and thermal inertia. Using existing models for predicting ignition temperature and thermal inertia, and correcting these models with the new information on effective absorptivity, it could be shown that the effects were significant but not very large. It was considered that the uncertainties in the model are so high that corrections for the effective absorptivity might be of minor importance compared to the other uncertainties and assumptions. An interesting observation was that the absorptivity of radiation from fires for products exposed to irradiation in the cone calorimeter decreased with increased exposure time, that is, the absorptivity decreased when the products darkened due to heat. This is surprising since, for example, wood that is darkened when exposed to heat obviously has a higher absorptivity in the visual part of the spectrum than fresh non-darkened wood. This is an important observation since it opposes the general view that heat transfer increases with increased thermal exposure due to darkening Finally, it was concluded that none of the studied materials showed a particularly low absorptivity in the infrared region and therefore none of the products stands out as particularly good reflector of radiation from fires. Several ideas were presented for how such spectrally tailored surfaces, with low absorptivity for radiation from fires, can be produced.
Measurements of the ion current between two electrodes have been conducted in a premixed propane flame and in a cone calorimeter in order to assess whether the ion current can be used for combustion diagnostics in general and for detection of ignition in a cone calorimeter in particular. It was seen that the ion current responds distinctly to where it is positioned in a propane flame and also to the fuel/air ratio of the flame. In the cone calorimeter the measured ion current shows clearly when ignition occurs. The ignition detected by the ion current measurement agreed with visual inspection. It was also seen that soot deposits on the electrodes do not affect the ion current in such a way the ignition detection could be jeopardized. However, short circuiting could occur if the electrodes were kept in a sooty flame long enough for the soot to completely bridge the gap between the electrodes. The latter scenario is not a problem from an ignition detection point of view since soot growth occurs after ignition has taken place. The general conclusion from the study is that no unforeseen obstacles with the use of ion current measurements in combustion diagnostics were observed.
The influence of additives on the interaction between radiation from fires and single water droplets has been investigated in detail. A literature study was performed on available information of radiation spectra from different types of fires. Based on this, four reference spectra were proposed that cover most of the different types of radiation that can be expected from fires. These reference spectra were used to compare the effect of different water additives and droplets sizes. Using Mie-theory it was found that increased atomization, down to a diameter limit of 1-10 μm, gives a better volumetric absorption efficiency. Decreasing the diameter further does not lead to improved volumetric absorption since the Rayleigh (small droplet) limit is reached, where the volumetric absorption is independent of diameter. Different additives were investigated with respect to increased absorption in the droplets. It was found, however, that it is not trivial to find non-flammable and non-toxic additives that give a significant improvement in absorption. Carbonated water was a potential candidate but the increased absorption was limited to a very weak band centered at 2300 cm-1. Since this coincides with the strong CO 2 emission band an effect could be seen when carbonated water interacted with radiation from clean flames. The maximum increase in volumetric absorption for carbonated water was 4%, occurring for a droplet diameter of 10 μm. Other additives gave better effects but they were either combustible (carbon nanopowder) and/or toxic to some degree.
The vibrational energy of water droplets has been investigated. Viscosity was neglected and only the lowest order symmetrical vibration, the quadrupole mode with m=0, was considered. An approximative solution was given by Rayleigh in 1879: w_vib=2a^2 ??r_0?^2 where ? is the relative vibration amplitude, ? is the surface tension, and r0 is the droplet radius at equilibrium, that is the radius of the spherical droplet. It was found that this solution agrees with the exact solution within a few percent for moderate values of the relative amplitude ?. The rationale of this study was to investigate whether dissipation of energy from a shock wave, e.g. from an explosion, into vibrational energy of droplets is a mechanism that needs to be considered on order to accurately model explosion mitigation using water mists. Traditionally droplet vibrations are not considered in such models whereas other mechanisms such as translational energy, heating, evaporation, and droplet breakup are considered. A useful parameter for quantifying the relative importance of vibrations as compared to linear acceleration of droplets is the ratio between vibrational and translational kinetic energy. This ratio is given by 3a^2 ?/(?p?r_0 v?_transl^2 ) where vtransl is the translational velocity to which the droplet has been accelerated by the shock front. This ratio is negligible for a particular severe explosion scenario where information on vtransl was available in the literature. For other cases vibrations might be of some significance but detailed information about the specific scenarios is needed to obtain detailed results. More work is needed in order to understand the effect of viscosity and higher order vibrations. Furthermore a model for the excitation of droplet vibrations by shock waves is required for modelling. Finally there is a lack of experimental knowledge on droplet size distribution for water mist interacting with a shock wave.
This work concerns the assessment of fire performance of interior materials in buses. The widely used test method ISO 3795/FMVSS 302 has received much criticism mainly based on the fact that the test is a small-scale method not suited for bus fires induced by for example fire in the engine compartment or fire in a tyre. Furthermore, test specimens are oriented horizontally, whereas much fire spread in a real bus fire occurs on vertically oriented products. Seventeen products were investigated: 11 textiles, four solids and two insulations. Three test methods were compared: ISO 3795, ISO 6941 and ISO 5658-2. Given the existing criteria for interior materials, it was found that ISO 6941 and ISO 5658-2 place harder requirements on the materials. When the three methods were compared, it was found that ISO 3795/FMVSS 302 and ISO 6941 are insufficient for simulating bus fires typically occurring today. Such fires are often initiated by a fire in the engine compartment or in a tyre and can hardly be simulated by small-scale methods as ISO 3795/FMVSS 302 or ISO 6941 even if the ISO 6941 method to some extent gives results similar to the established large-scale ISO 5658-2 method.