'Bridge-mixing' of gasified fuel vapors and simultaneous ignitions of different combustibles at flashover

'Bridge-mixing' of igniting fuel vapors gasified from different combustibles by thermal radiation during flashover is presented in this article. This explains why combustible items of different ignition temperatures appear to be ignited at roughly the same time in flashover. Sample cubes of polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), polycarbonate (PC), and wood are tested in a cone calorimeter at high thermal radiative heat fluxes of 50 and 70 kW m2. Two samples are tested each time. Different arrangements of the fuel tray are made to give different mixing of fuel vapors. It is observed that fuel vapors gasified from combustibles with different ignition temperatures are ignited simultaneously under some mixing conditions, depending on the geometry of the fuel tray under the cone. Mixing of gasified fuel vapors by the fire-induced airflow in rooms of different geometry is a key factor in igniting each combustible item. This releases more heat and generates flames to give conditions satisfying the flashover criteria.