For LA Metro we used sophisticated computer modelling tools to design an onboard fire suppression system that will protect passengers and achieve significant cost savings.
Opportunity
Conventional underground chambers constructed to house metro or tube stations, known as station boxes, feature high, cathedral-like ceilings to make smoke migration easier and aid passenger evacuation in the event of a fire. If the size of these structures can be reduced without compromising safety, it will minimise excavation and the amount of concrete needed during construction, cutting carbon emissions and cost. Utilising computer modelling techniques that have advanced the design methodology for tunnel ventilation, our engineers devised an alternative solution for LA Metro’s Crenshaw/LAX line.
Solution
After studying fire safety requirements, we recommended the installation of an onboard fire suppression system that would spray water mist inside carriages to contain the spread of fire. With rolling stock equipped with this technology, station boxes could be reduced in size and still allow passengers to be safely evacuated from a disabled train. Using computational fluid dynamics and our own STEPS pedestrian movement software, we demonstrated that a smaller box design had sufficient height to provide adequate smoke migration, giving time for passengers to make their escape. In our modelling we also calculated the temperatures on the ceiling and showed that concrete spalling (or flaking) would not occur and therefore there would be no falling debris to hinder an evacuation. Our solution is fully compliant with fire safety regulations.
Outcome
Optimising the size of the station box and the requirement for emergency ventilation infrastructure (with a reduction in fan sizes) is projected to shave millions off the cost of the construction of future underground stations. Onboard water mist systems are in the planning stages with the aim of installing them on both light rail and heavy rail rolling stock. With rolling stock equipped with this technology, LA Metro will be able to make a valid claim that it operates one of the safest transport networks in the world.