Development of a standard firebrand accumulation temperature curve for residential wildfire protection system

Climate change and severe heat waves pose a challenge as wildfires spread rapidly in wildland urban interface areas and are difficult for firefighters to control and extinguish. Therefore, one of the main factors for fire spread and the cause of residential fires is firebrands, which according to previous studies can be transported even by wind for kilometres. At this moment, there is no standard fire curve to simulate the thermal effects of firebrand accumulation in the exterior surfaces of dwellings, in order to provide any fireproof design solution. This paper presents a new standard fire curve to simulate the exterior accumulation of firebrands in contact with surfaces of dwellings, due to the indirect action of a wildfire. An experimental campaign was conducted, in which different type and geometries of firebrands were burned in controlled conditions until they reached the thermal pyrolysis state. The tests were also performed with controlled wind (1.3 m/s) to better simulated their behaviour. The temperature of the firebrands and the transfer temperature to the surfaces were measured using a test setup with metal plates and thermocouples. Using the data collected from numerous firebrand tests, it was possible to calculate a maximum characteristic temperature, calculated with a 95% confidence interval. Using this characteristic temperature curve, a design firebrand curve was proposed by using a simple fitting procedure and the minimum least square method. This new proposed fire curve is aimed be used in the design of protection systems of dwellings located in the urban wildland interface against the accumulation of firebrand projection due to a natural wildfire.