Model scale fire experiments in a model tunnel with wooden pallets at varying distances

• This report is part of the research project “Concept for fire and smoke spread prevention in mines”, conducted by a research group at Mälardalen University. The project is aimed at improving fire safety in mines in order to obtain a safer working environment for the people working for the mining companies in Sweden or for visitors in mines open to the public. This report comprises a number of model scale fire experiments conducted in a model tunnel at SP facilities in Borås, Sweden. The main purposes of the report are: - Obtain data which can validate models to calculate the total heat release rate of multiple objects - To investigate the influence on the heat release rate curve that a varying distance between the fuel objects will have. - To investigate the influence on the heat release rate, fire growth rate and time to ignition for adjacent fuel objects. The effects of ventilation are taken into account in the model.. The work in this report started with describing the theoretical basis of scaling theory and the determination of heat release rate at fire experiments, continuing with describing the experimental setup with the fuel load and instrumentation used. After that the experimental procedure and the experimental results were described and analysed. The results from the experiments were thereafter discussed and finally conclusions were drawn. The findings and conclusions of the study were as following: It was found that an increasing ventilation rate slightly increases the maximum heat release rate, which is in accordance with earlier research. The ventilation rate will have an influence on the fire growth rate. In the tests with the highest ventilation rate, a slower fire growth rate was displayed compared to the other two cases. This could possibly be explained by the fact that the height of the pile of wooden pallets (205 mm) was practically equal to the short side of the pile (200 mm) and the fire was started on the long side, thus as the longitudinal ventilation is increased less fuel area is exposed to the tilted flames resulting in that less parts take place in the combustion during the growth phase and thus the fire growth rate decreases. When studying the graphs of the various heat release rates it was found that when the distance between pile #1 and pile #2 increased to a certain level the ignition of pile #2 will be delayed resulting in that not all piles are burned with their maximum heat release rate at the same time. The delay in ignition of adjacent pallet can be distinguished by a “hump” before the peak value in the heat release rate curves. In cases with short distances between the piles the ignition of 3 adjacent piles took place almost simultaneously and resulting in a total heat release curve where the pallet piles burn at their maximum at nearly the same time, i.e. the effects of the delay of ignition is not really showing up in the time to reach maximum heat release rate. It was also found that the peak value of the heat release rate decreases as the distances between the piles are increased – from ~500 kW down to ~450 kW – as the curve is stretched out in time. The ignition data indicated that the time to ignition of adjacent piles would decrease as the longitudinal ventilation was increased. Further validation work should take place with respect to validating the experimental data with output data from theoretical models. Further studies and experiments should take place that vary additional parameters besides the distance between the individual fuel objects. This in order to make further comparisons with calculation models to predict the total heat release rates of complex objects, such as for example a vehicle.

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TECHNOLOGY

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Energy- and Environmental Engineering

energi- och miljöteknik

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