Numerical Simulation of the Evacuation Process in a Tunnel during Contraflow Traffic Operations

The purpose of this numerical research is to assess the evacuation process in a tunnel under the contraflow condition. Numerical simulations utilizing FDS+Evac codes associated with a fire dynamic simulator (FDS) model simulating a fire scenario are used to simulate evacuation and to predict the impact of a 100 MW fire scenario on the occupants inside the tunnel. Traffic and passenger conditions are based on real data from a tunnel in the UK. Two fire loads, 100 MW and 5 MW, are studied to represent an HGV and a passenger car fire. The 100 MW fire source, caused by an unexpected heavy good vehicle (HGV) catching fire, is located in the middle of the tunnel and at 20% of tunnel length to study the effect of fire source location on the usage of emergency exits and tenability thresholds. The dimensions and the inclination angle of the existing roadway tunnel are 1836 m (L) × 7.3 m (W) × 5 m (H) and 4%, respectively. It should be noted that the 4% inclination of the tunnel causes asymmetry propagation of smokes thus the visibility of the downstream and upstream from the fire behave differently. The maximum needed time to evacuate using all egress, the amount of fractional effective dose and visibility at the human’s height are analyzed. Simulation results indicate that when a realistic worst-case fire scenario is modeled, all evacuees can survive before the combustion gases and heat influence their survivability.

Fire resistance of composite slabs with steel deck under natural fire

PurposeMost of the numerical research and experiments on composite slabs with a steel deck have been developed to study the effect of fire during the heating phase. This manuscript aims to describe the thermal behaviour of composite slabs when submitted to different fire scenarios, considering the heating and cooling phase.Design/methodology/approachThree-dimensional numerical models, based on finite elements, are developed to analyse the temperatures inside the composite slab and, consequently, to estimate the fire resistance, considering the insulation criteria (I). The numerical methods developed are validated with experimental results available in the literature. In addition, this paper presents a parametric study of the effects on fire resistance caused by the thickness of the concrete part of the slab as well as the natural fire scenario.FindingsThe results show that, depending on the fire scenario, the fire resistance criterion can be reached during the cooling phase, especially for the thickest composite slabs. Based on the results, new coefficients are proposed for the original simplified model, proposed by the standard.Originality/valueThe developed numerical models allow us to realistically simulate the thermal effects caused by a natural fire in a composite slab and the new proposal enables us to estimate the fire resistance time of composite slabs with a steel deck, even if it occurs in the cooling phase.

Assessment of the Fire Effect on Water Balance Components Under Different Land Uses, Central Zagros, Iran Case Study

Background: Fire occurrence may lead to a significant impactin many terrestrial ecosystems. This study attempted to evaluate the effects of fire on the water balance components in the Central Zagros, Iran. The study used two modeling frameworks, including WetSpass-M and Bayesian Belief Networks to investigate the effect of fire on the amount of runoff, groundwater recharge and evapotranspiration. The first part of the study was a water balance simulation at a monthly scale. In addition, a Bayesian belief networks was applied to explore and understand key issues affect in the water balance after fire. Calibration and validation of the WetSpass-M model was performed without considering the effect of fire (2000-2014) and then the model was run again to with the fire scenario by reducing manning roughness coefficient and increasing the θ coefficient. Results: Calibration and validation were performed before finalizing the simulation. A Nash-Sutcliff coefficient of 0.61 and 0.58 was obtained during the calibration and validation respectively. The analysis of the water balance components results depicted that fire has increased the amount of runoff and it has reduced the amount of groundwater recharge and actual evaporation especially in the sparse forest and poor, medium and good rangelands. Conclusions: Water balance components of each class, i.e. sparse forest, poor, medium and good rangelands were different under fire/non-fire scenarios. The percentage of change in the water balance components were used for comparison. The results of Bayesian model for post-fire scenario showed a significant increase in runoff due to reduced vegetation in the area. Both simulated groundwater recharge and surface flow have showed a reduction rate in the fire occurrence scenario. A similar conclusion was obtained from probabilistic Bayesian model due to reducing vegetation cover and surface changes. Actual evapotranspiration component for the poor rangeland has dropped off significantly. Therefore, there is a need for monitoring hydrologic dynamics of the lands with a high risk of burning.