The role of surrounding buildings on the accumulation of embers on rooftops during an ember storm

Abstract

Results are presented for tests of ember accumulation on buildings during an ember storm. Specifically, the experiments investigate the role of upstream buildings on the accumulation of embers on the rooftops of a building. Experiments were run for three target buildings for three different wind directions per building. The upstream array of buildings varied in both layout (staggered and regular grids of buildings) and in terms of the number of upstream rows of buildings and streamwise spacing between the buildings. Results indicate that each of these parameters, i.e. spacing, layout, and number of rows, influences the accumulation rate. In all cases tested the mass of embers that accumulated on the rooftops was less than 18% of the mass that would have accumulated were the building removed. For buildings with roof heights similar to those of the upstream buildings the accumulation rate increases by up to a factor of 10 compared to when there are no upstream buildings. The lowest spacing between buildings produced the largest accumulation. When the target building roof height was larger than upstream buildings, this change was less pronounced. However, the variability in the accumulation rate between nominally identical tests decreased when the upstream buildings were present.