Thermal performance of fire resistive materials II. A multi-layer one-dimensional heat transfer model for fire resistive materials protecting a substrate

This report is the second of a three-part series concerning the characterization and modeling of the thermal performance of fire resistive materials (FRMs). These materials are currently qualified and certified based on lab-scale fire tests such as those described in the American Society for Testing and Materials (ASTM) E119 Standard Test Methods for Fire Tests of Building Construction and Materials [1]. While these tests provide an “hourly” rating for the FRM, these ratings have no direct quantitative relationship to the performance of an FRM in an actual fire, e.g., a 2 h rating does not mean that the FRM will protect the steel (or other substrate) for 2 h in a real world fire. Computational heat transfer models offer the potential to bridge the gap between laboratory testing and field performance. However, these models, whether basic one-dimensional or more complex three-dimensional versions, depend critically on having accurate values for the thermophysical properties of the FRM (and substrate) as a function of temperature, to be used as inputs along with the system geometry and fire and heat transfer boundary conditions. In part I of this series, procedures for determining a consistent set of these thermophysical properties were presented. Now, in part II, a computational onedimensional multi-layer model for the heat transfer from the fire, through the FRM, to the substrate is developed and verified by comparison to the results of a series of slug calorimeter experiments, previously conducted in the Building and Fire Research Laboratory (BFRL). Ultimately, similar performance simulations will be executed for ASTM E119-type tests and even real fires.