ABSTRACT
Fire scientists and engineers have created a world of mathematical and computer-based analytical tools to explain and predict fire growth and behaviors. These tools are widely used to plan sprinkler systems, smoke detection and control systems, and other fire safety measures. Many have provided insights into why postfire physical indicators look the way they do and how reliably they reflect fire events that took place. This has led to improvements in the accuracy of scene investigation (particularly by demonstrating the limitations of traditional indicators). Today’s fire models include highly developed computer programs that rely on basic principles of heat and mass transfer, and chemical thermodynamics to predict fire growth and effects in known conditions. There is a demand today for applying these models to actual past fires to predict a variety of factors in both civil and criminal fire investigations with the intent of proving a fire occurred in one specific manner. Recent tests have demonstrated that even in room fire is well documented by prefire measurements and identifications of fuel loads (e.g. furniture and wall and floorcoverings), the accuracy of computer models to predict temperatures, heat flux, and growth is determined largely by the duration of the fire and the involvement of multiple fuel packages. The longer the fire burns, the less accurately it “follows” the predictions of even the best models. Real fire events rarely have comprehensive prefire data and any models would face additional uncertainties of fuel types, heat output, mass, and ventilation. Many of the models can be linked to a visualization program, which produces colorful animations of the computer’s fire predictions and its effects. These animations are compelling “evidence” when shown to a jury. Recent cases have shown that the best models can be “forced” to predict fires in conditions for which they were never intended, and, most critically, never validated. Computer models have been validated (by appropriate American Society of Testing and Materials (ASTM) standards) to suit many fire situations and have been demonstrated to yield reliable predictions for compartment fires with simple fuel loads and well-documented features (ventilation openings, dimensions, and fuel properties) over the initial growth phase. These are useful for testing alternate hypotheses in an investigation. Complex fires in rooms with multiple fuel packages have not been successfully modeled to duplicate real test fires beyond their growth phase. The result of such models should not be used in court to demonstrate how a large, complex fire actually behaved.
