Fire Spread Caused by Combustible Facades in Japan

With regard to fire safety for exterior walls of a building, fire-resistance performance is considered, according to the current building standard law of Japan. And it was revealed that the fire safety is not specifically regulated from the viewpoint of reaction-to-fire performance, such as fire propagation caused by combustible materials or products which are installed on the exterior side of fire-resistant load-bearing walls. Actual fire issues in the world have shown that massive façade fire could occur at the exterior side of building wall even when the wall itself is fire-resistant. In previous studies of the authors, a test method of façade fire was tentatively proposed for evaluating the vertical fire propagation over an external wall within the same building. Furthermore, especially at the high-density residential areas in Japan, fire spreading would occur mostly from window to window between adjacent buildings, while walls are not burning by façade fire. But in case of combustible façades, such as insulating materials, combustible coating, or even sandwich panel are installed on the wall surface, once they are ignited, façade fire would occur and accelerate both the fire propagation in the same building and the fire spreading to the adjacent building. In this paper, results of fire tests on combustible façades are discussed from the viewpoints of both vertical fire spread along façades and fire spread between adjacent buildings assuming the densely populated residential area in Japan. The tentative criteria were determined based on the time to reach 500°C and duration time exceeding 500°C on façade surface for vertical fire spread along façade. As for intensively burned cases, at 2500 mm height from upper edge of the opening, specimens of exterior thermal insulation system with 200-mm thick expanded polystyrene (EPS), aluminum composite panel with polyethylene core and wooden façade without fire-retardant treatment continued exceeding 500°C for 3.1 min, 5.7 min, and 3.6 min, respectively, that were longer duration compared with specimens of resin painting (approximately 1 min). On the other hand, the another tentative criteria were determined for horizontal fire spread to an adjacent building based on the duration time exceeding the calibration test’s peak incident heat flux on opposite surface 2000 mm from façade surface for horizontal fire spread to an adjacent building. At 500 mm height from upper edge of the opening, specimens of exterior thermal insulation system with high-density 100-mm thick EPS and wooden façade without fire-retardant treatment continued exceeding the peak incident heat flux of calibration test for 13.1 min and 13.6 min, respectively, while one specimen of resin painting and aluminum composite panel with polyethylene core continued for shorter duration of 4.2 min and 5.8 min, respectively, even though they showed relatively high peak façade surface temperatures.