Flammability and burning behaviour of fire protected timber

Abstract

Decarbonization has driven the construction industry to rediscover biobased, but inherently combustible, materials like timber. To avoid compromising fire safety, reaction to fire of timber can be effectively reduced by fire retardant surface coatings or impregnation treatments. Using a combination of simultaneous thermal analysis, microscale combustion calorimetry and cone calorimetry, vacuum-pressure impregnated (boron free, phosphorus-based) plywood was tested against plywood coated with a thin layer of water-based fire retardant intumescent coating (melamine free, phosphorus-based). Comparing the peak heat release rate (pHRR) and total heat release (THR) of the three plywood samples, the impregnated was lowest, and the coated was lower (pHRR −34% and −20%, THR -45% and −21% respectively) relative to the untreated plywood. In contrast, the coating layer postponed sustained flaming for longer than impregnated wood and delayed burnthrough, effects critical to the growth rate of a developing fire. Better understanding of the assessment of flammability of fire protected timber has been obtained using cone calorimeter data supported by microscale analyses. The results challenge the simple flammability ranking based on total heat release, and highlight the need for further development of a methodology for comparing different fire protection strategies for timber.