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

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 reduced the amount of oxygen in the pyrolysis zone, 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 in combustion. The ignition time of the treated samples was at least 1.5 times longer than that of the untreated samples at a 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 can be expressed as a function, which is approximately equal to 0.8 \({\rho \over {\mathop q\limits^{\,\,\,.\,''} }}\) . The soot yield for both PA1 and PA2 increased with the rising heat flux, approximately 0.006 to 0.007 kg/kg at higher heat flux. The total heat release and total oxygen consumption 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, and CO and CO₂ yields. However, flashover propensity of PA2 ranged from 0.25 to 12.07, slightly higher than that of PA3. Further research is being undertaken to further refine the formula to better meet the safety requirements.