Investigating the fire-retardant efficiency of intumescent coatings on inclined timber: a study on application strategies and heat transfer mechanisms

The impact of intumescent flame-retardant (IFR) coating location on the fire-resistance of inclined timber samples was studied using a multi-imaging system that integrated visible wavelength, short-wavelength infrared (SWIR), long-wavelength infrared (LWIR), and Schlieren techniques. Weight loss post-initial ignition was monitored using a weight scale, and a scanning electron microscope (SEM) was employed to observe the microstructure of both coated and uncoated surfaces post-burn. Samples were inclined at 30˚, 45˚ and 60˚ to study the effects of inclination on fire-retardant efficiency. Four coating strategies were compared: top surface, bottom surface, one side surface, and both side surfaces, against an uncoated control. Quantitative results revealed significant reductions in burning intensity and fire spread when coating was applied to the bottom surface and both side surfaces, attributed to the inhibition of convective heat transfer from underneath the timber samples. The mechanisms of this inhibition were considered to be the termination of gas-phase combustion and impediment of pyrolysis product escape. Furthermore, the fire-retardant efficiency diminished with increasing inclination angles, especially for samples coated only on the top or one side. Conceptual models were developed to understand the mechanisms of fire-retardance and heat transfer inhibition. This work offers critical guidance for the application of fire-retardant coatings and may enhance cost efficiency in fire safety, particularly for individual elements of timber structures such as beams, columns, and frames.