Theoretical model for further development of intumescent substances to remediate smoldering in wood fiber insulation panels
Wood fiber insulation boards, as many other wooden materials, are susceptible to smolder. This type of slow and flameless thermal degradation has three upmost important drawbacks. First, smoldering can develop unseen until damages are noticed; second, it does not need any external heat to keep progressing, thus behaving as a self-sustaining process; third, it may shift into flaming combustion. Although wooden insulation materials are very competitive as insulators, its use is not permitted in several countries beyond mid-rise buildings due to smoldering hazard. As measuring of physical parameters is difficult and expensive at high temperatures, the objective of this investigation was to develop a theoretical model that comprises most relevant physical phenomena in order to serve as a supportive tool for further development of fire-retardant substances. The constructed model presents the novelty that it can simulate the self-sustaining smoldering without needing any external radiation heat, but only the self-heating generated by its own exothermic reactions. The model was built based on a program of experimental testing that included thermo-gravimetric analyses and differential-scanning calorimetry, being able to predict particle degradation at different heating rates and oxygen concentrations with errors of about 7,5 %. The adequacy of the model was also compared at the structural scale against a non-standard cone calorimeter test with terminal switching off heat radiation to emulate self-sustaining smoldering, which was used as model validation showing fits of about 23 % in consideration of mass loss, mass-loss rate and temperature profile. A comprehensive sensitivity analysis comprising 60 distinct parameters permitted to thoroughly assess the influence of each model input parameter, which is being presented as a ranking from the most to the less influencing parameters that prevent or foster self-sustaining smoldering. Several unexpected conclusions raised, positioning species' densities, capacities and reaction activation energies as the most important parameters. To the best knowledge of the authors, this is the first model that can simulate the self-sustaining smoldering of wooden insulation materials, so it is expected to contribute on further development of fire retardant compounds for wooden products.