Experimental study of the large scale flammability of wood cladding at the wildland-urban interface

The aim of this work is to improve the understanding of the fire behaviour of building materials used in the wildland urban interface at a large scale. To this end, wood cladding was exposed to the heat flux from the burning of a cistus hedge ignited by a spreading fire front in a fuel bed of excelsior litter. Six experiments were performed with different configurations: hedge/cladding distance, cistus bulk density, hedge length. During the experiments, the assessment of the cladding ignition was observed by camera. Wind direction and velocity were measured continuously since the tests were conducted outdoors and wind is a significant driver of flame spread. Heat fluxes and temperatures were also measured in order to compare the intensity of the thermal aggression on the cladding coming from the burning hedge. When the distance between the hedge and the cladding was 3 m, the wood did not ignite even when the wind was in the direction of propagation towards the cladding. In these cases, the maximum heat flux was 18 kW m−2. This value did not allow the ignition of the wood cladding. When the distance was reduced, the ignition of the cladding depended on the wind direction. When the cladding was ignited, the heat fluxes from the burning hedge could exceed 100 kW m−2. •Ignitability of wood cladding at the Wildland-Urban Interface.•Fire spread from a vegetation hedge to a building material.•Comparison of the critical heat flux for ignition at material and large scale.