DEVELOPMENT OF A PYROLYSIS MODEL FOR ORIENTED STRAND BOARD

Abstract

Oriented Strand Board (OSB) is a widely used construction material responsible for a substantial portion of the fire load of many buildings. To accurately model the response of OSB to fire, Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Microscale Combustion Calorimetry (MCC) tests were carried out to construct a thermal decomposition model using a numerical solver, ThermaKin2Ds, and a hill climbing (HC) optimization algorithm. The model was determined to consist of two distinct processes. The first process is a single step water vaporization. The second process is a chain of four consecutive reactions representing thermal decomposition of the organic constituents of OSB. The experiments and modeling revealed that the first two of the four reactions are endothermic, while the last two are exothermic, and that the net heat of decomposition is near zero. The heat capacities of condensed-phase species and heats of combustion of evolved gases were also determined from inverse modeling of the DSC and MCC tests, respectively. Controlled Atmosphere Pyrolysis Apparatus II (CAPA II) experiments were performed at 35 kW m-2 and 65 kW m-2 of the radiant heat flux. The sample bottom temperature data obtained at 65 kW m-2 were used to determine the thermal conductivities of condensed-phase species. The complete pyrolysis model of OSB was subsequently validated by comparing the experimental CAPA II mass loss rate profiles with the model predictions. The undecomposed OSB density was found to vary both along the sheet surface and through thickness. However, these density variations had only a minor impact on the key features of the mass loss rate profiles.