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This work presents the results of experimental and numerical analysis on tunnel fires in an attempt to improve existing knowledge on the fire dynamics and related safety measures in various tunnel fire scenarios. Results are grouped into four parts in which the effects of tunnel wall coating, inclination, tunnel obstruction and existence of secondary fire source in close vicinity were investigated on tunnel fire characteristics. A 1/13 longitudinally ventilated scaled tunnel model constructed based on Froude modeling was used in the experiments with ethanol pools as the fire source. Numerical simulations were carried out using Fire Dynamics Simulator code. The focus was on critical factors in the safety research community including heat release rate (fire load), burning rate of fire and tunnel temperature distribution, which were measured across a wide range of ventilation conditions, pool size and depth. Results emphasized that the overall variations in the burning rates of fires at different ventilation conditions was a function of competing factors that affect the heat release rate, mass transfer coefficient and cooling effect of the airflow. The application of absorptive wall coating led to considerable reduction of radiative heat flux to upstream of fire. Burning rate and the heat release rate of fire showed an increase as high as 125 % under the effect of the secondary fire source, emphasizing the need to account for possible secondary fires in tunnel safety design. In case of blocked fire tests, the results from experiments as well as simulations indicated that due to changes in local ventilation velocity and flow pattern upstream of the fire, heat release rates tend to increase as high as 0.7 MW/m2 compared to un-blocked fire under certain test conditions. It was also shown that tunnel inclination is an influential parameter that affects the smoke movement and ventilation requirements of tunnel considerably. Ph.D. - Doctoral Progra

An analysis of tunnel fire characteristics under the effects of vehicular blockage and tunnel inclination

It is known that the blockage and inclination conditions of tunnels are among the important factors affecting fire safety considerations, as these factors could change the characteristics of possible fire incidents as well as smoke movement in tunnels. In the present work, we analyze the variations of the tunnel fire burning rate, heat release rate and smoke backlayering as being functions of these two factors. Ethanol pools were used as fire sources in a reduced scale tunnel model with longitudinal ventilation ranging between 0 and 1.5 m/s. The blockage ratio of the tunnel, which was defined as the ratio of the cross-sectional area of the blockage to that of the tunnel, was tested under three cases: 0% (i.e., no blockage), 14% and 56% blockage. The latter two blockage ratios respectively correspond to that of a typical small vehicle and a railroad carrier. The tunnel inclination grade was varied between -6% and +3% to represent uphill and downhill slopes. Numerical simulations were also performed using Fire Dynamics Simulator (FDS) to rationalize some of the experimental results. Measurements and predictions indicated that the blockage affects the burning rate of tunnel a fire due to changes in the air entrainment at wake flow, local ventilation over the fire and flame dragging. Increasing the ftre-blockage separation distance had an adverse effect on the burning rates. The temperature results emphasized the effect of blockages on tunnel ceiling temperatures, which increased as high as 300% compared to that of the no blockage case. The results indicated the major effects of the tunnel sloping grade on the fire heat load as well as the tunnel ceiling temperature. The critical ventilation velocity was achieved in the range of 0.75-1.25 m/s for the limiting cases of -6% and +3% tunnel inclination, for which a fit was proposed as a function of inclination grade. Finally, a statistical model based on an analysis of variance approach was applied on the obtained results, which demonstrated that among the factors contributing to the fire heat release rate variations in this study, the ventilation velocity accounted for 45% of the variation, followed by tunnel blockage at 25%, and inclination at 19%

An experimental study on the burning rates of interacting fires in tunnels

Multiple fires may occur in close proximity in process industries, power generation and fuel storage facilities and confinement conditions such as tunnels, which can lead to a considerable alteration in fire characteristics and safety design. The topic is of significant importance to the fire safety research because there is little work in the literature that investigates the case of interacting fires, which have a destructive potential. In this work, we study the effects of an adjacent fire source on the burning rate and heat release rate characteristics of tunnel fires. Square ethanol pools of 10 and 15 cm in size and 0.22-1 cm in depth were used as fire sources in a reduced scale tunnel model. Ventilation to the tunnel was varied between 0 and 1.5 m/s. Pool fires were configured in single and dual pool orientations. Variations in the pool fire burning rates were discussed as being functions of pool size and depth, and a result of the interaction with the secondary fire. The maximum burning rate enhancement factor, defined as the ratio of the parameter for interacting fires to non-interacting ones, was shown to be 2.3. This was due to the enhancing effect of the secondary fire on the heat feedback to the fuel, and the increased combustion mass transfer. Tests with relatively larger pool sizes burned faster, with an advanced onset of the transition to a bulk boiling phase, which was attributed to the controlling heat feedback mechanism associated with the pool size

AN EXPERIMENTAL STUDY ON THE CHARACTERISTICS OFn HEPTANE ETHANOL MIXTURE POOL FIRE IN A REDUCED SCALE TUNNEL

Fire accidents in recent decades have drawn attention to safety issues associated with the design, construction and maintenance of tunnels. A reduced scale tunnel model constructed based on Froude scaling technique is used in the current work. Mixtures of n-heptane and ethanol are burned with ethanol volumetric fraction up to 30 percent and the longitudinal ventilation velocity varying from 0.5 to 2.5 m/s. The burning rates of the pool fires are measured using a precision load cell. The heat release rates of the fires are calculated according to oxygen calorimetry method and the temperature distributions inside the tunnel are also measured. Results of the experiments show that the ventilation velocity variation has a significant effect on the pool fire burning rate, smoke temperature and the critical ventilation velocity. With increased oxygen depletion in case of increased ethanol content of blended pool fires, the quasi-steady heat release rate values tend to increase as well as the ceiling temperatures while the combustion duration decreases

Experimental Investigation on the Mass Loss Rates of Thin-Layered n-Heptane Pool Fires in Longitudinally Ventilated Reduced Scale Tunnel

Thin-layered n-heptane pool fires are burned with varied pool depths under longitudinal ventilation velocities ranging between 0.5-2.5 m/s in a reduced scale tunnel model. The combined effects of ventilation, pool size, and depth are investigated on the heat release rate, temperature distribution, and mass loss rate of fire. The gas temperature distribution and heat release rate results indicate that the critical ventilation velocity is achieved around 1 m/s in the scaled model, corresponding to 3.6 m/s in the real scale tunnel. It is observed that the gas temperature downstream of the fire increases at 2.5 m/s ventilation due to an enhancing effect of oxygen supply to the fire and increased flame deflection towards the leeward side of the pan. Results show that maximum heat release rate and total heat release normalized by fuel amount tend to occur at critical ventilation velocity. The measured mass loss rates show a considerable increasing trend with pool depth