Skalningseffekter av medelstora pölbränder i syrereducerad miljö

Sammanfattning: This bachelor's thesis focuses on how scaling the pool diameter affects flammable liquids in an oxygen reduction system (ORS). This topic in the study of pool fire behavior in hypoxic air has been only lightly discussed in previous literature. Therefore, the goal of this thesis work is to further broaden the understanding of hypoxic air. This is done through experimental studies, examination of prior literature and comparison between the two. Experiments were conducted with heptane and methanol contained in round steel vessels with a diameter of 0.2 m or 0.15 m, placed inside a hypoxic chamber. Fire behaviors were studied in oxygen concentrations (Xo2) of 21 and 15 vol%, as well as the liquids’ limiting oxygen concentration (LOC). The results that were found indicate that, for luminous and sooty fires such as heptane, an ORS has a larger reducing effect on fire behaviors, including peak heat release rate (HRR), peak HRRPUA, flame height and temperature compared to non-luminous and less sooty fires such as methanol. The fire reducing effects of hypoxic air were more prominent for the 0.2 m vessels than for 0.15 m. It was found that the biggest reduction in both peak HRRPUA and flame height was obtained when XO2 was reduced, even though the percentage-based reduction of vessel area was greater than the percentage-based reduction of XO2. When down-scaling the pool diameter the fire-reducing effects were weaker when done in ORS opposed to normal atmosphere. This indicates that ORS is more effective for larger fires than small fires. CO/CO2 yields were largely unaffected by hypoxic air for both flammable liquids. The liquids’ LOC differed when different pool diameters were used, but no correlation between LOC change and pool diameter change was found. The conclusions that can be drawn from these results are that even though ORS at a XO2 of 15 vol% does not prevent all fires from starting, it does have a reducing effect on the heat release rate and fire spreading capabilities of a pool fire. Furthermore, the results indicate that ORS has increased effectiveness with a larger size of pool fires. When using current standards, ORS works as an effective retardant of pool fires. To fully prevent pool fires with ORS, additional measures must be taken in research and current date regulations to further improve the use of hypoxic air in fire protection systems.