Limit-Based Fire Hazard Model for Evaluating Tunnel Life Safety

Despite the simple one-dimensional symmetry of a tunnel with a longitudinal ventilation flow, risk analysis often comprises resource intensive and complex calculations. The purpose of this article is to present a simple yet precise limit-based model for assessing the possibility for a safe tunnel evacuation. To estimate the model uncertainty, fire dynamics calculations were compared to experimental data. The calculations performed well compared to experimental test data, showing an average difference between 5 and 40% in predicting the time available for evacuation, when criteria for visibility, air temperature, CO, CO₂ and O₂ concentration and heat flux were calculated. For steadily growing fires, visibility showed a low sensitivity to variability in input parameters with a relative difference at 9% compared to experimental data. Due to several factors it was not possible to estimate the accuracy of HCN calculations. Visualizing the hazards in a time–distance diagram revealed visibility to be the key indicator for calculating ASET for a broad set of plausible input parameters. This resulted in a simple expression for calculating ASET and consequently a simple condition for evaluating life safety.