Metro and urban rail systems: A passenger-safety assessment
Not just the sub-systems “Vehicle”, “Stations”, “Tunnel” and “Operation” need to meet the regulatory safety requirements individually, but also need to interact in a manner which ensures the safety of the overall rail system, considering proportionality and societal expectations. On behalf of Wiener Linien (Vienna Public Transport), TÜV SÜD Rail is currently working on an integrated risk assessment of the total system (vehicle, infrastructure, operation) of all metro and urban rail vehicles to evaluate whether safety objectives would be fulfilled in case of a fire.
On behalf of Wiener Linien, TÜV SÜD Rail carried out integrated risk assessment of all metro and urban rail vehicles and investigated how fire and smoke would impact on rail infrastructure in the city of Vienna. The network of underground lines is currently undergoing expansion, with the addition of a new link of the U5 underground line. This line will be integrated into existing stations and expanded by building new stations. To continuously ensure the objective of protecting personal safety, the design of the underground stations must allow safe passenger evacuation, either through self-rescue or rescue by a third party.
In a first step of the analysis, the existing rolling stock of the underground system has been examined to assess the potential of fire developing from a technical defect. According to the risk assessment, the highest risk potential for a fire incident in rail vehicles is posed by the possibility of vandalism in conjunction with luggage catching fire. To determine the effects of such a fire incident in the vehicle and the following stations, the assessment investigated the characteristic progress of the fire with the help of a “design fire”. A “design fire” is a scenario that defines the fire development over time and likely intensity of the fire under conservative framework conditions.
To determine the “design fire”, the project evaluated practical fire tests already completed and, in addition, performed another fire test. The resulting fire development was used as the basis for evaluating criticality of the underground stations in terms of flue-gas volume flows from the vehicle into the station. Depending on the specific situation, i.e. the layout of rescue routes and the spatial geometry at the station in question, the scenario shows the necessity and the required dimensioning of smoke protection systems in tunnels and at stations. These systems must result in a low-smoke layer above platform level and the rescue routes, to ensure passengers can escape in case of a fire incident. The calculations involved are performed by computer simulation (computational fluid dynamics), to determine the possible development of the fire spread in the vehicle and indicating the effects on the infrastructure at the stations. For this purpose, fire simulation is combined with an evacuation simulation to determine the necessary or required evacuation times, taking into account the time taken for smoke and toxic gases to build up to a critical level.
The low smoke layer in the underground station depends on various factors, including station ventilation and the installation of platform screen doors.
The project classified all existing stations in various categories. The collaboration between TÜV SÜD Rail and Wiener Linien within the scope of comprehensive system assessment (vehicle, infrastructure, operation) to assess protective objectives is based on a solution-focused technical exchange between experts.
As a result of the project, the personal safety offered by the overall system is now documented in a verifiable manner. In addition, the managers can identify possible opportunities of improvement, enabling them to implement further actions.