REDUCTION OF FIRE HAZARDS DOWNWIND OF WIND-DRIVEN FIRES BY TREE BARRIERS PART 1: A PRELIMINARY EXPERIMENTAL AND NUMERICAL-SIMULATION STUDY

摘要

In large urban fires, wind-driven fires are particularly disastrous in heavily-populated open areas such as parks or school yards where there is little time to evacuate the people and particularly children to safety. One measure that has recently received some attention is to use planted tree barriers around the periphery of open areas. Such barriers lead to a reduction of the heat arriving at the wake region by heating the foliage instead. Additional heat sinks can be activated by installed water sprays directed at the foliage. Consequently, the fire-protection measure of using appropriate tree barriers may thus provide, during a difficult earthquake fire eruption, sufficient precious additional time to evacuate people to safety. The purpose of the present experimental and numerical simulation study is to seek some preliminary data so that the effectiveness of this fire-protection measure can be assessed. The experiments, because of the relatively large size involved, are difficult and expensive to carry out, and hence only a few tests could be completed. Numerical 3-D field-model computations were also carried out to simulate the essential physical features of the experiments to insure the validity of the simulation model. The experiments showed that the tree barrier does create an extended wake region behind the tree barrier with low temperatures and velocities, thus demonstrating the potential of using the tree barriers as a fire-hazard mitigation measure in wind-driven fires in populated open areas. The numerically-simulated results correspond well with what was observed in the experiments. Additional numerical studies based on prescribed leakage velocities demonstrated that there exists an optimum leakage velocity, which would correspond to specific barrier characteristics and provides an optimal wake region near the ground for fire-hazard mitigation considerations, and this optimum agree essentially with the experiments carried out in the overall study.