Development of Tunnel Ventilation Systems Strategy and CFD Analyses Results for Ottawa LRT Project

Abstract

Numerical modeling and analysis for the design of the tunnel ventilation system of Segment 2 of the Ottawa Light Rail Transit (OLRT) project is currently progressing. Segment 2 is mainly underground beneath Ottawa’s downtown core and includes three underground stations, two portals and the connecting tunnel. The tunnel section comprises approximately 2.5 km of twin-track tunnel running beneath the downtown core area. The Tunnel Ventilation System (TVS) is comprised of tunnel ventilation fans, jet fans (at portals), and ventilation shafts, which extract contaminated air from the underground system to grade during a fire incident. Based on both specific project requirements and NFPA130 requirements, the mechanical ventilation systems for the underground transit stations are to be designed to ensure a tenable environment is provided for the specified egress period. This paper summarizes the efforts to develop the tunnel ventilation system (TVS) strategy and Computational Fluid Dynamic (CFD) modeling and analysis to assess the duration for which tenability of the egress routes can be maintained by operation of the TVS for one of the underground station of the OLRT project: Rideau Station. The CFD analysis is used to determine the Available Safe Egress Time (ASET). This may then be compared with the time required to evacuate persons from the station, i.e. the Required Safe Egress Time (RSET).