ARCHIVED - Breathing easier in Montréal tunnels
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February 08, 2008— Ottawa, Ontario
In March 1999, a transport truck caught fire in the Mont Blanc Tunnel – an 11.6-kilometre stretch linking France and Italy. Fueled by a load of margarine, the fire burned for more than 50 hours, trapping 40 vehicles and killing 39 people. Sadly, the inferno may have been lessened if authorities had not pumped in fresh air, forcing smoke to spread throughout the tunnel.
Two years later, commuters got a scare when a small vehicle burned in the Ville-Marie Tunnel in downtown Montréal. Fortunately, there were no deaths. But when firefighters arrived, the smoke was too thick for them to do their jobs safely. As a result, the firefighters lodged a complaint about inadequate tunnel ventilation to the Ministère des transports du Quebec (MTQ).
|Entrance to Louis-Hippolyte-La Fontaine Tunnel.|
In 2003, the MTQ approached NRC fire protection researchers to evaluate emergency ventilation strategies in Montréal's two largest road tunnels: the Louis-Hippolyte-La Fontaine Tunnel, which runs under the St. Lawrence River and connects Montréal Island with the Trans Canada Highway, and the Ville-Marie Tunnel.
Under normal conditions, mechanical ventilation systems in tunnels provide users with comfortable temperature and humidity conditions, while minimizing air contaminants. If a fire occurs, these systems become critical for ensuring safe evacuation conditions and safe access for firefighters by controlling the accumulation of smoke.
"During a fire, the tunnel authority needs to activate some fans in a supply mode to inject fresh air so that trapped motorists can breathe, and activate other fans in an exhaust mode to remove the smoke," says Dr. Ahmed Kashef of the NRC Institute for Research in Construction (NRC-IRC). "How the fans should be used depends on the location of the fire, the size of the fire – even the weather conditions."
Evacuation scenarios were available for both the La Fontaine and Ville-Marie tunnels, but traffic patterns and volumes had changed significantly since these tunnels were built in the 1960s and '70s. The MTQ realized it needed to revise its emergency ventilation plans based on scientific data. "They asked NRC for help because of our expertise in doing field tests and numerical modeling," says Dr. Kashef.
To collect useful data, the NRC team conducted several field tests that involved closing a tunnel for six hours overnight and lighting a controlled fire. "In order to get permission, we had to prove to the MTQ that we would not damage the tunnel and that we needed to close it to achieve a higher level of safety," says Dr. Kashef. "Up until then, the La Fontaine Tunnel had never been closed to traffic."
|Field test in La Fontaine Tunnel.|
Dr. Kashef and his colleagues used a special fire burner developed at NRC to produce a small vehicle-sized fire. "We had to make sure there would not be any damage to surveillance cameras or light fixtures," says Dr. Kashef. Meanwhile, the team measured temperature, air velocity, air flow and other variables, and filmed how the activation of various tunnel fans affected the dispersal of smoke.
Back in the lab, NRC researchers combined the data from several field tests to create a numerical model for each tunnel that can simulate larger tunnel fires, such as a burning bus or truck. "Our model allows us to test, under a wide range of scenarios, which fans will ensure an escape route is free from smoke and provide a safe environment for firefighters," says Dr. Kashef. "We can then tell the tunnel operator how to achieve the safest outcome – wherever a fire occurs – using the fans they have right now."
|Ville-Marie Tunnel in downtown Montréal.|
So far, the researchers have completed the La Fontaine Tunnel study, which generated both tunnel ventilation and tunnel upgrade recommendations for the MTQ. According to Dr. Kashef, the tunnel ventilation recommendations were followed successfully during a small fire in 2006 that was brought under control. The MTQ is now planning a major overhaul of the La Fontaine Tunnel, which will include a new evacuation route as recommended by NRC. "Right now, the passenger conduit is shared by some of the tunnel's fans, which may be used to supply fresh air or exhaust smoke during a fire," he explains.
This year, the NRC team expects to complete its study of the Ville-Marie Tunnel, which exceeds two kilometres in length and has multiple entrances and exits. Over the long term, Dr. Kashef and his colleagues would like to help create Canadian standards for tunnel ventilation and improve existing North American standards.
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