FIRE SAFETY | WTC


FIRE SAFETY SPOTLIGHT


Fire Safety was among the many and varied topics discussed about the development and operation of underground spaces at last year’s World Tunnel Congress


As would be anticipated for a major tunnelling conference, there are many technical topics - including Fire Safety - threading throughout the many dozens of papers and presentations. As such, these threads are most frequently parts of the narratives discussing different new tunnel projects or tunnel systems, from either a design or construction perspective, or both (see box: Immersed Tube Tunnels). Existing tunnels and their operations provide more of


the home for papers that have more focus on Fire Safety. There were not quite so many such papers, however, and perhaps that is understandable, to a degree; the dedicated section that held the mostly Fire Safety papers was ‘Operational Safety, Maintenance and Repair’ and had so much to cover in managing the function and upkeep of different underground spaces. In WTC 2024, the papers in ‘Operational Safety,


Maintenance and Repair’ offered four with ‘fire’ explicitly in the title and focus (see box: References), out of a total of 32 papers. What is there is most interesting and spotlights on some key aspects are given below.


DALIANGSHAN NO1 EXPRESSWAY TUNNEL, CHINA The study of the smoke exhaust from fire scenarios in a long twin tube road tunnel to be equipped also with cross passages, and some inclined shafts, was the focus of a paper1


looking at design strategies. The project was


Daliangshan No1 expressway tunnel, in Sichuan Province, China. Using different fire scenarios and locations within


each main tube, and near or far from the inclined tunnel, the smoke removal efficiency of each case was modelled using one-dimensional analysis. The results showed some scenarios couldn’t


effectively control the fires in the main tunnels, due to insufficient upstream air flow velocity and downstream exhaust capacity. But near the inclined shaft there was greater efficiency than provided for by the envisaged cross-passages. Design optimisation increased the ventilation ducting


capacity in the cross-passages, with ducting stepping up from the initially proposed 7.1m2 9.9m2


cross-sectional area to . This change would ensure that each and all of the


cross-passages would have ventilation ducting able to meet the requirements for fire smoke exhaust. This was


22 | July 2025


coupled with routing smoke exhaust downstream in the main tunnels, along with longitudinal smoke induction.


BRUSSELS NORTH-SOUTH RAILWAY TUNNEL The Brussels North-South Railway Tunnel was built in 1946 and is located at a critical part of the network, but it doesn’t meet current interoperability requirements for safe evacuation and structural fire resistance. The conference paper2


results from a Masters


thesis, at Ghent University, that found the use of a performance-based approach worked to find an acceptable level of improved structural fire resistance. The particular combination of tools and simulations used enabled a more specific and realistic thermal calculation than provided for in design standards with benchmark fire curves, the researchers reported. They concluded that oversized standard fire curves


lead to overestimation in fire protection and structural improvement. But, noted that it was “a matter of debate” if intensive computational 3D finite element model (FEM) calculations are needed to implement fire protection. Additionally, they note that, “To reduce costs, fire


safety engineering only (mostly) investigates the highest temperatures and not the temperature evolution in the longitudinal direction through the tunnel model.” Related to that, they see research opportunity into the


progress of spalling in fire scenarios in the 79-year old Brussels North-South Railway Tunnel.


STRUCTURAL EFFECTS: NUMERICAL- PHYSICAL COUPLING STUDIES Further on the modelling of fire effects on structures, another paper3


at the conference discussed the


“promising alternative” of numerical-physical coupling for investigating tunnel structural behaviour under fire scenarios. As opposed to full-scale fire tests in laboratories, the


approach combines numerical simulation with some physical testing - as coupled, or integrated approach to modelling. The simulation is of the entire structure while the physical test concerns a specific component only. The research, from Tongji University, in Shanghai, has


shown the method gives good results, including for stress fields and displacement fields, respectively,


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