| The direct revelation of fire and smoke inhalation is an immediate danger to passenger's life in case of fire in underground tunnels.The understanding of fire behaviors is very critical to take effective decisions.Past studies related to tunnel fire dynamics were mostly related to ventilation conditions with an assumption that both tunnel ends are open.In specific cases of tunnel fires like a fire inside the train cabin,fire during the construction of tunnel and fire in tunnel corridor,both ends of the tunnel may be completely or incompletely blocked or sealed,depending on circumstances which significantly disturb the ventilation inside the tunnel.So the study about tunnel fires related to blocking of tunnel entrances is very rare.Computer-based simulation work is very useful,flexible,and low cost in assessing the consequences of tunnel fires.This study utilizes the potential of Fire dynamics simulator software(FDS)to evaluate the fire characteristics inside the full-scale tunnel.A series of numerical simulations were carried out to examine fire behaviors under the combined effect of different fire locations,different sealing entrance ratios at different sealing time.Heptane fuel was used as a source of heat and smoke.A series of characteristic parameters like temperature above fire source,longitudinal smoke temperature distribution,longitudinal oxygen distribution,heat flux near a fire source,CO concentration at the entrance as well as the smoke temperature at the entrance were calculated.Results showed that temperature over fire source decreases as we move away the fire location from tunnel center and with an implementation of sealing at entrances,peak value increases and maximum values appear in case of un-equal sealing(75%,100%)and earlier the sealing time,earlier the temperature achieves a peak value for short time and then decreases.Furthermore,the longitudinal smoke temperature distribution is symmetrical in symmetrical sealing cases along both sides of the fire source when placed at the center.The peak temperature value increases by increasing the sealing ratio and decreases by increasing the sealing time.The difference is large between sealing cases and no sealing case and it decays exponentially.Moreover,as we move the fire source away from the tunnel center,the distribution is no more symmetrical on both sides of the fire source with higher values on the left side because of flame inclination towards the nearby entrance.Heat flux near the fire source always decreases as we move away from the tunnel center and with an implementation of sealing at the entrance,heat flux decreases but increases with increasing sealing time.When the fire source is very close to the entrance,the phenomenon is not the same because the temperature is very high at the entrance.In this case,heat flux increases by increasing sealing ratio,and maximum heat flux is recorded in case of un-equal sealing 75%,100%.CO concentration at left entrance always increases as we move the fire source away from the tunnel center and by increasing sealing ratio but there is no significant effect of sealing time was reported.Moreover,there is no effect of changing location on oxygen concentration inside the tunnel until sealing is implemented.Increasing sealing ratio decreases oxygen level due to smoke accumulation inside the tunnel and earlier the sealing time less will be oxygen because earlier sealing restricts the flow of fresh air inside the tunnel.Sealing time has no impact on the smoke temperature rise at the entrance but it certainly increases from 200? to 300? by changing the fire location without sealing.By implementing the sealing of 75%,100%,it rises to more than 800?.So this un-symmetrical sealing factor should be in consideration for firefighters during fire tragedy. |
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