Volume 1, Issue 5 (September 1973)
Analytical Prediction of the Thermal Response of Decomposing Materials in Fire Environments
An analytical model is presented which accurately predicts the thermal response of decomposing materials in fire environments. The model is the same one developed for the design of reentry and space vehicle heat shield materials including the Apollo heat shield. The analysis handles one dimensional transient thermal conduction with decomposition, surface reactions, and transpiration with a variety of surface boundary conditions. Both temperature and density dependent properties are utilized for proper characterization of the thermophysical behavior of a material. Basic details of the thermal processes involved are given as well as the scope of the model. Thermal analyses of three different types of materials exposed to two different fire environments are presented. Two materials, gypsum wall board and a spray-on fiber material, were tested in a controlled subscale fire at the Avco Laboratories, while the third, a reinforced plastic, was tested at Underwriters' Laboratories in a safe-column furnace.
Measured thermal properties used to make the predictions are presented along with the methods of measurement. The test environment is also discussed in terms of heat transfer rates, enthalpy, and nature of the gases. The behavior of plastics and their reaction to a fire environment is discussed and related to the model. Results given for the predictions made show excellent correlation with the measured temperatures and weight losses. Finally, the utility of the model is discussed relative to predicting the fire response of various materials without the aid of extensive testing.