Experimental study of pinewood samples incorporating multiple flame-retardant additives under varied heat fluxes in a cone calorimeter

Abstract In this study, pristine pinewood samples and those treated with flame-retardant additives were examined to evaluate their fire risk. The combustion process was delineated into four stages: release of flammable volatile gases, reduction of thermal penetration depth, sample deformation to optimize heat absorption, and the onset of smoldering combustion involving char formation. It was discovered that the synergistic effects of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), triphenylphosphine (TPP), and (NH4)2HPO4 not only facilitated the decomposition of the samples but also lowered the surface temperature and diluted the oxygen concentration, thereby prolonging the ignition time, particularly at heat fluxes of 25 or 30 kWm− 2. The incorporation of Na2CO3 alongside other additives predominantly impacted the second stage of the combustion process, significantly contributing to the reduction of thermal penetration and dilution of oxygen concentration in combustion. The ignition time of the treated samples was at least 1.5 times longer than that of the untreated samples at lower heat flux. Notably, stable burning was more pronounced at higher heat fluxes for treated samples, and the mass loss rate of these samples was comparatively lower. The thermal penetration depth as a function expressed by ca. 0.8 \(\frac{\rho }{{\dot{q}}^{"}}\). The soot yield for both PA1 and PA2 increased with the heat flux rising and was approximately 0.006 kg/kg, at higher heat flux. The total heat release (THR) and total oxygen consumption (TOC) were observed to be lower for the treated samples. Upon analyzing the fire risk, it was determined that the performance of additive combination PA2 was superior, indicated by lower values in key risk indicators such as heat release rate, mass loss rate (MLR), and CO and CO2 yields. However, flashover propensity of PA2 ranges from 0.25 to 12.07, slight higher than that of PA3. Research is ongoing to further refine the formula to better meet human safety requirements.