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Transportation tunnels became one of the easiest ,fastest and shortest way of transportation as it provides a more straight and simplified route in terms of geometry for a trip and commercial delivery .
But in the event of fire occurrence transportation tunnels turn from a very modern and fast transportation infrastructure to a very dangerous place regardless of how they have been constructed . since tunnels are made of the masonry materials and they are usually build as an excavation inside a mountain while the materials being used in it except electrical cables and features are all nonflammable materials ,
So the causes of the Fire inside tunnels are almost due to the cars and vehicles passing by and they are almost same common fire causes everywhere as it may happen as an accident of cars or trucks or may be as an electric-fuel sparks of cars and lorries . While big fires are due to the tankers which carries flammable fluids and petroleum and the initial spark of these fires are the most important considerations though it becomes all fire investigations target, which may be a result of extra heating of breaks , tires or a burn in electrical cables inside a vehicle .
Fires occur in tunnels far less frequently than in buildings, however because of the unique nature of a tunnel fire, they are more difficult to suppress and extinguish, and usually get more attention.
In theory, the frequency of tunnel fires is related to variables such as tunnel length, traffic density, speed control, and slope of the road. Each variable has to be accounted for when comparing different tunnels. For example Urban tunnels tends to have a higher fire rate than other tunnels and an event frequency span of about one fire per month to one fire per year only applies to either very long tunnels or heavy traffic volume, while a large majority of tunnels report far fewer fires .
There are major concerns and challenges for tunnel owners and public about the fire life safety in transportation tunnels and this is due to several aspects, since tunnels are usually two way two lane or one way two lane and when it becomes longer and bigger fire risks increases due to extra traffic volume which means extra passengers and extra life so the controlling difficulty increases too . As in the event of a fire which wasn’t predicted and controlled at it’s time in a long tunnel regardless whatever was its causes , first of all the fire makes a sudden stop in the traffic flow behind it thus it will increase number of cars and vehicles behind it and may lead them to be involved in the fire especially if they are closer to each other thus the size of the fire may be bigger while the produced smoke will cover the area and significantly decreases the sight distance towards zero according to burning materials, so as a result the traffic flow of the other side will stop if the tunnel is a tow way tunnel meanwhile all car passengers will try to escape from the fire and it’s smoke and at that time amount of fresh oxygen in air will be considerable decreased which is no longer is enough for human breath and car engines with having very poor sight distance passengers would die trying to escape either because of they couldn’t breathe or they couldn’t see the safe path and confused running toward the fire .
While in the event if the fire was predicted in a reasonably time then firefighters were send to the location probably they will face a lot of obstructions and delays because of the jammed traffic in front of them or the long length of the tunnel relatively to the location of the fire and the firefighters approach to it .
Globally Tunnel fire policy and protection raised to it’s optimum after some very dangerous fire accidents happened like Monti blank tunnel which is between Italy and France in which fire accident killed 39 people while the Cablecott tunnel fire killed 7 peoples and may other tunnel fire accidents ,so the Governments trying to gain a super best policy to deal with the fire disasters in transportation tunnels through their large and small scale Fire tests and through their past tunnel fire studies . while in most cases the transportation of flammable materials and goods loaded on trucks were the triggers of tunnel fire disasters according to NFPA ( National Fire Protection Association ) final report 2008 ,
tunnels due to their limited access and egress pose unique fire safety challenges, particularly on firefighting due to both restricted access to the fire site and the confined nature of the tunnel. With the inclusion of dangerous goods within tunnels, fire safety issues are greatly intensified .In addition the hazards and risks associated with the transportation of dangerous goods should be considered in light of the systems and procedures which may be adopted to mitigate such risks. There will be some forms of dangerous goods in which no single system or procedure may be utilized to handle an incident and therefore these types of dangerous goods may be totally prohibited from the tunnel if an alternative is available or the risk of such an incident is taken and therefore the substance be allowed .It should be noted that legislation for the transportation of Dangerous Goods in each State and Territory exists. The relevant Authority should be involved in the decision to allow dangerous goods to be taken through tunnels. the Tunnels, due to their limited access and egress pose unique fire safety challenges, particularly on firefighting due to both restricted access to the fire site and the confined nature of the tunnel.
Moreover the impact of the tunnel fire disasters in terms of it’s fatality and damages to properties has made a lot of efforts on authorities to try their best in order prevent these accidents so the different studies has been made on fire detection systems and some of intelligent sytems , cameras, smoke and heat detectors are the initial fire detectors which predicting fire in it’s initial stages , i.e smoke stage and alerting tunnel control room or showing the smoke to the inspectors and indicating the location of the fire so that authorities will be in formed directly and are able to control tunnel entrances and operate alarm systems and activate firefighting systems ,while in recent studies mentioned that their should be emergency smoke ventilation system with a high performance beside normal ventilation system in side tunnels in order to handle the large amount of smoke while the passengers are escaping , and the presence of fire alarm buttons on the wall of tunnel with suitable intervals may be very help full in the event of fires as if it is connected to tunnel operating room and active firefighting systems like water suppression systems which enables a direct and active control of the passengers on the fire,
furthermore there are debates on how to install intelligent systems, i.e. (NFPA) final report has pointed to some Automatic incident detection systems and intelligent video cameras which are activated with a lot of actions , in which automatically detects vehicles and trucks meanwhile it record incidents and tells tunnel operators to observe the event in question and makes respond options to the operator to take appropriate action in addition to that report described some other aspects regarding passenger evacuation assistants like lighted signs and guides for the passenger escape route that are universal and consistent- visual which every one can understand it and they are visual even in very dark smokes .
Smokes and it’s related dangerous problems are major design concerns when designing a Ventilation system for a tunnel , traditionally three approaches has been used in the design of road tunnel ventilation systems , Longitudinal Tranverse and semi transverse ventilation systems for short less than 250m tunnels natural ventilation is suitable .
1 Longitudinal ventilation system
Longitudinal ventilation can be generated with a system of fans, which may be spaced intermittently at the ceiling above the roadway or may be housed in central ventilation buildings on the tunnel . Intermittent vent shafts, at points where air is either supplied or exhausted, can be introduced to increase the practical length of tunnels in which longitudinal ventilation can be effectively applied. The airflow direction follows the traffic direction which means more energy efficient because the system takes advantage of the vehicle and truck pushed air ( Piston effect ). Under normal free flowing traffic, the tunnel is usually self-ventilated. The concentration of pollutant like (CO2 )levels in the tunnel increases in the direction of airflow. In a fire emergency, smoke will be pushed downstream of the fire site towards the exit portal or captured at strategically located exhaust shafts. The Memorial Tunnel Fire Ventilation Test Program (MTFVTP) had concluded that a longitudinal ventilation system employing jet fans is highly effective in managing the direction of smoke spread for heat release rates up to 100MW (with 3.2% grade) as shown in figure 1 . Longitudinal ventilation can be achieved by using either jet fans mounted at the tunnel ceiling or by nozzles located at the tunnel ceiling called Sccardo nozzle as shown in figure 2 . For jet fan system, the fans deliver airflow at a very high velocity (e.g. 20 to 35 m/s) and can create a momentum that will entrain the surrounding air to move in a desired airflow direction. For Saccardo nozzle system, air is injected at a high velocity (e.g. 30 m/s) from the nozzle. Similar to the jet fan system, the air exiting from the Saccardo nozzle can create a momentum that will entrain the surrounding air to move to a desired airflow direction.
2- Full-transverse ventilation system
Full-transverse ventilation system supplies outdoor air and extracts exhaust air uniformly over the full length of a tunnel. Therefore, a supply air duct and an exhaust air duct running along the tunnel are always required. In this system, the amount of exhaust air equals the amount of supply air and the airflow is transverse to the longitudinal axis of the tunnel. With a full-transverse ventilation system, the pollutant level as well as the air velocity in the tunnel are relatively uniform. The ventilation concept is illustrated in Figure 3 . In a fire emergency situation, smoke will migrate from its source along the underside of the ceiling. The full-transverse ventilation system attempts to control smoke and hot gases by extracting the smoke through the exhaust openings along the ceiling. The design aims at maintaining a smoke free layer for passenger evacuation. MTFVTP had shown that extracting smoke quickly from a location that is as close as possible to the fire can significantly reduce the migration of smoke and heat in undesirable directions, however, the extraction point needs to be oversized.
3- Semi-transverse ventilation system
Semi-transverse ventilation system either supplies outdoor air or extracts exhaust air uniformly over the full length of the tunnel. Therefore, it always requires a supply air duct or an exhaust air duct running along the tunnel. With a semi-transverse supply or semi-transverse exhaust air system. The ventilation concept is illustrated in Figure 4 . In a fire emergency situation, the semi-transverse supply system will operate in reverse mode. Smoke will be captured over the length of the tunnel, with outdoor air entering the tunnel through the portals or adjacent air intake shafts. The aim is to maintain a smoke clear layer for passenger evacuation.
In addition to that the tunnel inclination angel has a great roll in the discharge of the induced smoke from fire according to an experiment by (Quintiere 1988) which he made a 1/25 scale semi circular tunnel with adjustable angle to horizontal From the observed smoke movement patterns, the shape of the buoyant plume (shape of smoke ) inside the tunnel depends on the tilted angle. The smoke plume would be tilted along the tunnel floor due to gravity. The bending angle depends on the tunnel angle. A bigger tilted angle would give larger amount of smoke flowing in the tunnel.
In some modern tunnels like Channel tunnel ( Between France and Great Britain ) third tunnel has been constructed between two main tunnels and it is connected with other two main tunnels by transverse shafts , so that in case of fire passengers can escape from the tunnel which is on fire to other tunnel via rescue shafts and this shafts are well closed and protected against smoke leakage ,
other new Ideas can be debated on how to create better solutions fire accident crisis in the tunnel , like providing U turns for emergency exits only, I believe that it is possible to design U turns in side two way tunnel with suitable intervals while it should be controlled by intelligent gates which opens them only in emergency situations to allow cars return to tunnel portals and escape from fire. or designing electro-mechanic slid water nozzles beside normal water suppression nozzles these slid water nozzles are suitably spaced along tunnel ceiling i.e. 70 m spacing and it should be long enough to cover this 70 m which means (10) cars lengthen 7m each length and controlled by intelligent system so that it will be concentrated on the vehicle which is on fire by the tunnel operator .
Soft Ground Improvement by Jet Grouting Method
Paper No . 2
Prepared by : Umed Abdulkhaliq Aziz
CIEN E4245
Tunnel Design and Construction
Prof : Nasri Munfakh
Date : 11/30/2012
Two Level Bracing Solider Pile SOE
Prepared by : Umed Abdulkhaliq Aziz
CIEN E 4130
Design Of Construction Systems
Prof : Vincent Tirolo Jr
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