Structural hazards of smouldering fires in timber buildings

Smouldering, a slow, persistent, and flameless form of combustion has only been observed in few fire experiments of mass timber compartments. Smouldering is a phenomenon well-understood in the wildfire community, but is not yet recognised as a hazard in the fire safety design and fire-fighting of modern timber buildings. This paper presents observations and analysis following the cessation of flaming in CodeRed, a series of three open-plan compartment fire experiments with a mass timber ceiling and columns. The formation of nineteen smouldering hotspots was observed, which developed along the edges of timber elements where heat losses were minimised. Conventional and infrared imaging was used to track the hotspots over the 48 h following the cessation of flaming, observing smouldering hotspot initiation, spread, self-extinguishment, suppression by both hose and rain, and transition to flaming. Structural failures due to smouldering were studied, including the formation of holes in the ceiling and encapsulation, and the collapse of a column. This paper shows that smouldering can be a structural hazard in timber buildings that has not yet been addressed in the literature of timber building fire safety.