Download the provisional programme here:
ISAVFT 2026 Provisional Programme
Session 1: Sustainability in Underground Design & Construction
In these days of easy international travel, the world seems to be becoming more homogenous. You can get good sushi in Graz and Brisbane, good steak in Osaka and Graz, and schnitzel everywhere including Osaka and Brisbane. Why then are our approaches to tunnel fire safety so different? For real cultural experiences when you travel, forget the food – go and look at the tunnels. This paper notes differences in approaches to ventilation, fire suppression and tunnel operation and, within the limits of our knowledge, tries to rationalise them. Simply thinking about the differences may assist advancements in any of the jurisdictions, perhaps in a direction not identical to any of them.
Australia’s vehicle fleet is evolving with the gradual uptake of alternative fuel vehicles and the establishment of the national New Vehicle Efficiency Standard in 2025. Furthermore, the New South
Wales and Federal Governments are investing billions of dollars in the transition to renewable energy. All tunnels in Sydney, New South Wales, constructed after the M5 East tunnel (2001) are required under their Environmental Conditions of Approval to have zero vehicle emissions from the tunnel portal. Achieving portal emissions requires ongoing operation of energy-intensive, costly major ventilation fans.
Both Brisbane and Melbourne have at least two tunnels each which commenced operations with zero portal emissions but have successfully introduced portal emissions following a consultative process with the state regulatory authorities, resulting in substantial environmental, sustainability and commercial benefits.
The objective of this article is to:
1) Demonstrate technical feasibility and precedence for portal emissions in Australia and overseas,
2) Quantify commercial and decarbonisation benefits of adopting portal emissions in Sydney and,
3) Identify a regulatory pathway to enable the New South Wales Government to activate road tunnel portal emissions, whilst meeting community expectations.
The research identified an annual cost saving of approximately $4,880,000 in electricity expenditure for a single Sydney tunnel case study if night time portal emissions were to be adopted.
The research also outlined a complex regulatory pathway to implement portal emissions, with a potential time frame exceeding three years. Opportunities to fast track the process are also identified.
Brisbane has a large dedicated busway network that has progressively expanded over 25 years and includes a significant number of tunnels. The fire safety systems and operational requirements have evolved progressively adapting to changes in vehicle types, safety strategies and available system provisions. This means that the tunnels can have varying provisions and operations.
The tunnels that were initially developed are at an age where system upgrades are currently being considered. These upgrades need to not just consider equipment replacement/refurbishment but also reconsideration of strategies, operations and the potential incorporation of new systems. Ideally upgrades would bring these tunnels to a level of safety equivalent to new modern standards. Various constraints however mean that this is not necessarily possible.
Work has been undertaken to develop a framework in which to assess the existing infrastructure in order to determine the requirements to arrive at a position where the tunnels can be considered to meet fire safety requirements So Far As Is Reasonably Practicable (SFAIRP). This is considered to be a health and safety requirement that needs to be achieved. This paper describes the considerations that were undertaken in order to arrive at a process that would work within the constraints of a large operating busway system. These considerations include items such as legal requirements, physical limitations, operational constraints and new vehicle technology. The work undertaken can offer guidance into how older existing infrastructure can be assessed in order to meet fire safety requirements.
Sewer networks, often containing deep tunnel networks, present distinctive ventilation phenomena associated with the effects of sewage flows on ventilation flows.
Newton’s method, for single variables and in matrix implementations, has been found to be broadly useful for predicting ventilation flow rates and pressure distributions in sewer networks across varying flow regimes, explaining field observations not previously understood.
Case studies are reported for three relevant flow regimes:
• Stratified flow
• Entrained air
• Vented siphonic flow
Session 2A: Road Tunnel Case Studies
The Gotthard roadway tunnel, in service since 1980 as a single bidirectional bore, is being upgraded to a twin-tube system: a new bore is first driven parallel to the existing one, and the original bore is then refurbished, so that each tube finally carries unidirectional traffic. This paper presents the carriageway ventilation design, which combines concentrated smoke extraction through a false ceiling with longitudinal jet-fan control. The design is verified by one-dimensional network calculations, targeted three-dimensional CFD of the jet-fan and ventilation-station flows, and transient PI-controller simulation of the fire response across the staged construction and final operating states.
Road tunnels serve the public for long periods, typically close to a century. These projects are delivered over three to ten years (depending on length and complexity), with design assumptions and construction quality having a major impact on the Operations & Maintenance (O&M) needs. This impact often manifests as gap between the intended and real performance of the functional systems that make up the road tunnel.
This paper discusses such gaps with a focus on fire and life safety systems, given their role in managing health and safety risks for motorists, O&M staff and emergency services. The discussion centres on the validation of initial design assumptions—particularly those concerning human behaviour in crisis, fire and traffic interactions and integrated system performance. When these are tested against real-world operational conditions, the results might diverge from the specified performance requirements, introducing safety and business continuity risks that in turn can lead to significant unforeseen expenditure.
Based on this discussion, a framework is proposed to better identify and validate key design assumptions for fire detection, fire suppression, and smoke management systems throughout the O&M phase. Rooted in process safety and systems engineering principles, the framework aims to enable iterative design changes that help reduce or close the gaps identified after construction. It is put forward to raise awareness among key stakeholders, particularly those involved in developing the reference design and resulting technical requirements for new projects.
The Brazilian national and state highway network is expanding very rapidly, particularly in the São Paulo area, the nation’s economic hearth. The new national regulation ABNT NBR 17175 “Sistemas de ventilação em túneis rodoviários e urbanos — Requisitos” (“Ventilation systems in road and urban tunnels ─ Requirements”) issued on 27.08.2024 regulates all aspects related to road-tunnel ventilation. It provided the much needed technical and administrative framework for authorities, construction companies and designers and enables the development of a new generation of road tunnels with enhanced and consistent safety levels.
This paper presents an analysis of operational data from the Luboń Mały road tunnel on the S7 expressway in Poland, collected throughout 2024. The study evaluates the effectiveness of the tunnel’s ventilation and monitoring systems under varying traffic and environmental conditions. The analysis is based on a comprehensive dataset, including measurements of pollutant concentrations, airflow velocity and direction within both tunnel tubes, traffic volume and vehicle classification, and external meteorological conditions at the portals. The paper investigates correlations between traffic intensity, external weather, and resulting air quality inside the tunnel, assessing ventilation system performance in maintaining pollutant levels below safety thresholds.
The construction of flyovers to mitigate busy road inter-sections generates open, partially enclosed or fully enclosed roadways beneath it. The creation of such underpasses implicates specific fire and life safety requirements under NFPA 502. Short underpasses between 50 to 300 m in length are classified as Category A or X, which would not generally require mechanical ventilation for fire emergencies. However, given the requirement in NFPA 502 to demonstrate means of egress through engineering analysis, an ASET vs RSET using CFD tends to demonstrate the difficulty in achieving compliance without additional mitigating measures. This case study looks at a tunnel, which for the sake of this paper would be called Underpass X, with set of site-specific constraints— multiple traffic bores, architectural restrictions prohibiting vertical shafts, high traffic volumes and lanes, the presence of fuel tanker vehicles, and the absence of cross passages due to differing vertical road profiles—that made it particularly challenging to demonstrate egress tenability.
Based on CFD results, an ASET–RSET analysis concluded that vertical shaft openings would be required to keep the evacuation route tenable for the required duration of escape. Where high-level openings were not practicable, natural ventilation remained adequate for lower‑HRR fire scenarios (e.g., passenger cars or buses) but failed to maintain tenability for high HRR HGV and tanker fire. Therefore, the final design included a water-mist system and jet fans so that the required conditions for escape could be met for high HRR scenarios.
This paper discusses the challenges faced by designers on providing effective smoke control and tenable conditions for short tunnels. This underpass is used as an example, but the authors draw on other project examples and mitigations that have been used to resolve such scenarios.
Vehicle-induced pressure in road tunnels can influence the design of tunnel infrastructure, including cladding, signage, and ancillary equipment. This study investigates the ability of one-, two-, and three-dimensional modelling approaches to predict the transient pressure field generated by a heavy vehicle travelling through a tunnel beneath the tunnel crown. A series of simulations was undertaken using simplified and high-fidelity numerical models, and the resulting tunnel crown pressures were compared to assess the influence of model dimensionality and geometric confinement.
The results indicate that reduced-dimensional approaches capture the general characteristics of the pressure field but are limited in their ability to represent the effects of blockage ratio and lateral flow development. While the two-dimensional model reproduced the overall pressure-field structure observed in the three-dimensional simulations, it significantly overpredicted pressure magnitudes. The one-dimensional model successfully captured the general pressure trend but was unable to resolve local geometric effects associated with the vehicle-tunnel interaction.
Three-dimensional modelling provided the most representative description of transient pressure field within the tunnel. A sensitivity assessment further demonstrated that blockage ratio is a governing parameter controlling transient pressure field, with tunnel height exerting a greater influence than tunnel width. Comparison with established analytical theory showed close agreement with the predicted pressure differences and confirmed the suitability of simplified theoretical methods for preliminary assessments when the vehicle is travelling well within the tunnel, away from portal effects. The findings provide guidance on the applicability of different modelling approaches for the prediction of vehicle-induced tunnel pressures and the aerodynamic assessment of road tunnel infrastructure.
Session 2B: Railway Case Studies
Underground metro ventilation systems must satisfy thermal, pressure-control, and fire-life-safety requirements while minimizing plant space, installed capacity, energy consumption, and lifecycle cost. Conventional station trackway ventilation generally comprises Over-Track Exhaust (OTE) and Under-Platform Exhaust (UPE). OTE captures heat rejected by roof-mounted train air-conditioning equipment, whereas UPE is intended to extract braking and propulsion heat released beneath stationary trains.
This paper presents the engineering basis and numerical validation for eliminating UPE in selected underground sections of Chennai Metro Phase 2. The rolling stock incorporates regenerative braking and has no onboard brake resistors. Consequently, most recoverable braking energy is returned to the traction network rather than dissipated as under-car heat. Moreover, the restricted and obstructed space beneath the train limits effective extraction through conventional UPE openings.
The released under-platform space was repurposed as a fire-rated air-transfer path, enabling two reversible Tunnel Ventilation Fans (TVFs) in a single fan room to serve both station ends through ducts, dampers, and high-momentum nozzles. Performance was assessed using one-dimensional Subway Environment Simulation and IDA Tunnel modelling combined with targeted Computational Fluid Dynamics (CFD) analysis. Normal operation, prolonged station dwell, tunnel congestion, pressure transients, tunnel fires and station train fires were evaluated.
The analyses showed that an OTE-only configuration maintained acceptable tunnel and condenser-intake temperatures, controlled train-induced pressure transients, established the required fire airflow, and maintained tenable evacuation conditions. Nozzle-assisted supply reduced the representative tunnel-fire fan duty from approximately 130 m³/s to 60 m³/s. The case study demonstrates that UPE can be eliminated where rolling-stock heat characteristics, station geometry, operating scenarios and numerical validation collectively support its removal.
Tunnel ventilation and station HVAC systems can occupy up to 40% of the usable volume in an underground metro station. Stations developed in dense urban locations benefit significantly from compact Tunnel- and Station- Ventilation System (TVS and SVS) solutions, which minimises spatial footprint, construction cost, and, importantly, civil design complexity. However, such space-efficient configurations introduce complex airflow interactions between tunnels, trackways, and station volumes, necessitating advanced numerical modelling to verify performance across all operational modes and ensure compliance with stringent fire–life safety requirements.
This paper presents the integrated approach adopted by NCRTC to address thermal and pollution-related challenges in underground stations through advanced ventilation design, continuous air quality monitoring and intelligent control systems. Key parameters such as PM₂.₅, PM₁₀, CO₂, RH, Temperature and ozone are continuously monitored, enabling demand-controlled ventilation through BMS-SCADA platform. High-efficiency filtration and air treatment technologies are employed to enhance pollutants removal. CFD-based airflow and thermal simulations were used during the design stage to optimize air distribution, validate thermal comfort conditions as per ASHRAE 55 and minimize ventilation energy consumption. The study demonstrates how the performance-based ventilation design can effectively balance air quality, thermal comfort and energy efficiency, offering a scalable and replicable model for underground Rail transit systems in dense urban environments
This paper presents the design basis, operational philosophy and simulation-based verification of the Tunnel Ventilation System (TVS) provided for the four underground stations of the Delhi–Ghaziabad–Meerut Regional Rapid Transit System (RRTS), One-dimensional network simulations (SVS v6) and three-dimensional CFD analyses were used to verify performance-based approach with tunnel diameter of 6.5 meter and considering a 20 MW design train fire in the tunnel and 1 MW baggage fire in station areas , tunnel air and wall temperatures, critical smoke-control velocities and condenser-inlet conditions under various operating modes. The design follows international standards, including NFPA 130, with a strong focus on life safety and operational robustness. A push–pull ventilation strategy was adopted using tunnel ventilation fans to control longitudinal airflow during emergency scenarios, enabling smoke confinement within the incident zone and preventing its migration to adjacent tunnel sections and stations.
Many aging rail tunnels are in need of refurbishment, replacement, or entirely new installation of some fire and life safety systems features, including elements which were not available at the time or not required to the same extent as those required in current standards and best engineering practice. This paper presents a case study on the replacement of the tunnel ventilation system for a 1,500 m twin tube rail tunnel built in the early 20th century.
Studies present the proposed means to replace the original Saccardo nozzle ventilation system which has far exceeded its service life while also improving the system’s performance to meet the intent of current standards for fire and life safety. Providing an adequate replacement ventilation system is complicated by the tunnel’s inclusion of open cross passages spaced every 30 m along the length of the tunnel. In the design of new twin tube tunnels, cross passage doors are typically provided to prevent ingress of smoke to the non incident tube; however, operational constraints and cross passage doors operations and maintenance needs prevent installation of cross passage doors in this exiting tunnel. This case study presents the design of a ventilation system which considers the open cross passages between the two tubes their impact to requirements of the ventilation system to maintain smoke control while also ensuring safety for evacuees using non-incident tunnel. The effects of fire size and fire origin on potential ingress of smoke to the non-incident tunnel are also discussed.
Session 3A: Smoke Management & Egress
This paper presents results from eleven full-scale 5 MW and 20 MW fire tests conducted in the 1,520 m long Runehamar Tunnel to evaluate self-rescue conditions under low longitudinal ventilation velocities. Within the tested scenarios, near-zero velocity (~0 m/s) provided the most favourable bidirectional egress conditions by preserving smoke stratification. Initial ventilation velocities exceeding 2 m/s reduced stratification and degraded downstream egress conditions.
This study investigates smoke propagation and entrainment processes in inclined tunnels under two boundary conditions: a fully open tunnel and a blind-sided tunnel. Experiments and numerical simulations using Fire Dynamics Simulator (FDS 6.7.0) were conducted to analyze the influence of tunnel inclination and ventilation conditions on fire dynamics, smoke stratification, and entrainment behavior. The results showed that tunnel confinement significantly enhances the burning rate of the heptane pool fires compared with open-air conditions. Compared with the open configuration, the blind-sided tunnel generated higher temperatures and thicker smoke layers due to reduced smoke dilution and the suppression of stack-effect-driven longitudinal flow. Numerical simulations revealed a transition in smoke-layer stability around an inclination angle of 2°, above which interfacial instabilities and enhanced mixing developed. The study further demonstrated that entrainment strongly depends on the flow configuration. In the open tunnel, the relative velocity between the smoke and the air layers is lower than in the blind-sided case.
This paper presents an experimental study aimed at quantifying the efficiency of a smoke curtain in controlling fire-induced smoke flowing upstream in a longitudinally ventilated tunnel. This work extends and complements a previous numerical study (Narcisse et al., Efficiency of a smoke curtain in a ventilated tunnel, ISAVFT 2024) which had already demonstrated the potential benefits of such a system.
Experiments were carried out in a small-scale (1:20) plexiglass tunnel allowing flow visualization and measurement to be performed with standard cameras and a LDV (Laser Doppler Velocimetry) system. The air-helium modelling technique was used to reproduce the fire source buoyant flux.
The relevance and validity of the experimental model were first assessed by comparing small-scale measurements with full-scale data and correlations commonly used in tunnel fire engineering to estimate critical and confinement velocities for a given fire heat release rate.
The influence of the smoke curtain on the longitudinal flow was then investigated under non-smoke conditions in order to characterise the aerodynamic disturbances it induces and to measure the size of the vortex developing downstream of this curtain.
Subsequently, a series of tests was performed for several fire heat release rates and curtain heights to determine the blockage velocity (the required ventilation velocity required to contain smoke backlayering behind the curtain) at steady state. The transient phase was also examined with and without curtain to highlight the influence of the downstream vortex on the development of backlayering.
The results show that, for a given backlayering length, the use of a smoke curtain allows the required longitudinal velocity to be reduced (by up to 40%). This reduction has a direct impact on the design of longitudinal ventilation system in tunnels for fire safety issues.
Operation and maintenance of an emergency ventilation system for underground tunnels is a critical safety element an entire transportation system. Ventilation specifications that determine component selection utilize standard and non-standard requirements for equipment. Several different standards commonly referenced in specifications are discussed. IEC 61508, IEC 62278/EN 50126, and IEC 62425/EN 50129, address reliability and safety. NFPA 130, UL 429, CSA C22.2 No. 139, and UL 50 address systems and components used in ventilation systems. These standards and others, where each may use different assumptions, lifecycles, and acceptance criteria, are compared with respect to inclusion or reference in project specifications.
Backlayering refers to the formation of a stratified smoke layer that propagates upstream against the main flow and eventually reaches a steady state in a longitudinally ventilated tunnel during a fire. Numerous experimental studies have investigated the dependence of the backlayering length on the longitudinal airflow velocity. These studies generally show good agreement with the well-known empirical correlation proposed by Li, Lei, and Ingason (Fire Safety Journal, 2010). From a theoretical standpoint, however, this correlation has never been rigorously justified. To address this issue, the present paper reports preliminary experimental results obtained using a reduced-scale tunnel model. Vertical profiles of velocity and density were measured within a stationary backlayering, providing new insight into its internal flow structure. Based on these observations, we discuss the assumptions that could be made in an integral density-current-type model capable of formally predicting the backlayering length as a function of the fire heat release rate and the longitudinal ventilation velocity.
In underground railway operations, the smoke exhaust system is a critical safety asset. In traditional smoke system design, when equipment fails without a standby unit or when the design does not account for such a failure, the control logic interprets the equipment failure as a failure of the entire smoke exhaust system associated with that unit, treating it as binary condition, either fully operational or completely failed. This could potentially lead to unnecessary station closure and passenger disruption even when the system retains sufficient capacity to contain the smoke and maintain passenger safety.
This paper presents the concept of an “impairment mode”, as implemented in the Melbourne Underground Rail Loop (MURL) Fire and Life Safety (FLS) Upgrade project, detailing design concept, definition of some impairment scenarios, validation methodology and associated challenges. This discussion will be of interest to Tunnel Operators as well as engineers designing tunnel smoke exhaust systems.
Lighting and walkway configuration have a clear impact on movement in a smoke-filled rail tunnel. During design, analysis and evacuation modelling, walking speed should be adjusted according to the visibility and the configuration of the tunnel. The walking speed used in evacuation modelling in tunnels is often based on a tunnel environment which does not fully correspond with environments as seen in today’s newer rail tunnels. Newer rail tunnels are often equipped with adequate lighting and handrails providing an enhanced egress environment. If the walking speed used during design and analysis can be increased due to a more beneficial environment in new tunnels, it could lead to distances between exits being extended. Hence, a refined analysis can provide large cost-savings.
A refined egress analysis was commenced through a case study in the paper “A modified approach to walking speed within smoke-filled rail tunnels“ presented by the authors at the ISTSS conference in 2025. The paper focused on the lighting configuration and walking speed reduction due to visibility. The paper presented at ISTSS had a narrow perspective in terms of tunnel geometry and evacuation conditions being studied. However, it highlighted that the constant K, used for calculating visibility distance, as well as the minimum walking speed, can have a considerable impact on evacuation. This signifies the need of further sensitivity analysis. The paper being proposed for ISAVFT 2026 will be an advancement of the previous paper presented at ISTSS. The paper being proposed aim to broaden the tunnel geometries and evacuation conditions being considered. This will mainly be conducted through variation of fire heat release rate and walkway width.
Using CFD for fire modelling coupled with evacuation simulations, the study aims to highlight the shortcomings in current knowledge and provide a greater understanding for important input parameters when conducting egress analysis.
Session 3B: Innovations in Ventilation Design & Control
Hanshin Expressway Co., Ltd. has worked to achieve carbon neutrality by promoting energy conservation in equipment operations. Among all energy-consuming equipment in Hanshin expressway, tunnel ventilation systems account for a particularly large share around 50% of total electricity consumption. As a result, energy conservation in tunnel ventilation operations has become a key issue. This paper focuses on the longitudinal ventilation systems (central exhaust + jet fans) of existing tunnels that have reached the time for renewal. The findings of this study highlight that optimizing tunnel ventilation systems with consideration of control methods is essential for achieving energy conservation, cost reduction, and improved safety.
The West Gate Tunnel (WGT) adopts a multi-system tunnel ventilation strategy integrating air quality ventilation, high-pressure smoke extraction, longitudinal jet fan ventilation, maintenance ventilation and dedicated life-safety systems. Unlike conventional designs, these ventilation systems are separated to optimise their function and still coordinated through the control system to provide a compliant and safe design. Two main innovations are the use of low-pressure fans for normal ventilation and the inclusion of a maintenance tunnel allowing access to equipment without lane closures. The system demonstrates improved energy efficiency, operational flexibility and resilience, providing a new model for urban road tunnels.
High-speed trains moving through tunnels generate strong pressure pulses (both positive and negative) commonly known as the piston effect. The severity of these pressure loads depends mainly on train speed and direction, as well as the geometry of both the train and the tunnel. In longitudinal ventilation systems, jet fans installed inside the tunnel are directly exposed to these transient aerodynamic forces. There is uncertainty whether the piston effect can induce uncontrolled free spinning of the impeller, that may lead to potential mechanical failure or reduction in jet fan’s operational life.
To mitigate this risk, jet fans can be equipped with circular butterfly dampers that close when the fan is not in operation. These dampers significantly reduce the airflow through the fan when a train is passing, which reduces the effect of free spinning. While this configuration provides a practical solution for safeguarding fans in high-speed rail tunnels, it also introduces certain challenges, such as added aerodynamic resistance and increased maintenance requirements.
This paper explores the performance of jet fans with integrated butterfly dampers under various loading scenarios, based on both computational simulations and experimental
testing. Key aspects evaluated include aerodynamic behavior and the overall effectiveness of the fan-damper assembly. The study contributes to a better understanding of how to integrate jet fans into high-speed railway tunnel ventilation systems to ensure reliable and resilient performance.
Eglinton Crosstown (referred as Line 5) is a new 19 km transit line in Toronto which includes a 10km underground portion with 12 underground in-line stations, three underground interchange stations and ten at-grade stops. One of these three interchange stations integrates with the existing Line-1 at a single aerodynamically integrated Eglinton station. The upgrade of existing Eglinton station (Line 1) and the tunnel to the south of the station were included in the project. Upgrade of the tunnel portion included addition of two axial fans and associated dampers installed in a TVS fan room west of the Berwick portal located south of the station, as well as two axial fans and associated dampers installed north of the existing station. An important design element was the use of portal doors at each tunnel entrance to prevent excessive flow bypass and ensure precise control of smoke direction during emergency scenarios.
This paper presents a comprehensive engineering analysis of TVS and portal door integration. A primary focus is the development of a calibrated loss factor to account for air leakage at the door-track interface. This was achieved through an iterative coupling of 1D network modelling and 3D CFD analysis, ensuring that the mechanical ventilation could overcome “short-circuiting” at the portals to maintain tenability.
The paper further describes the operational coordination required between portal door and fan sequences across various fire scenarios. Comparison of the modelling predictions versus outcomes of Testing and commissioning are discussed. By comparing predicted leakage rates with field-measured performance, this case study offers valuable insights into the practical challenges of using portal doors as active aerodynamic boundaries in complex urban rail environments.
High-fidelity computational fluid dynamics (CFD) simulations are widely used in ventilation and fire engineering but remain computationally demanding, particularly for parametric analyses and scenario-based assessments. Physics-Informed Neural Networks (PINNs) have emerged as a promising surrogate modelling approach capable of approximating CFD solutions while embedding governing conservation equations directly into the training process. By enforcing physical laws as soft constraints, PINNs can achieve physically consistent predictions with fewer labelled data than purely data-driven models. However, practical implementation still relies on CFD-generated datasets for supervised training, which limits overall efficiency gains.
Structured reduction of CFD-derived datasets is examined as a means of enhancing PINN training. Self-Organizing Maps (SOMs) are employed as an unsupervised clustering technique to identify representative flow samples and eliminate redundancy while preserving dominant aerodynamic features. The approach is evaluated using two-dimensional flow around a circular cylinder, a canonical bluff-body configuration exhibiting separation and wake dynamics representative of flow phenomena encountered in ventilation and fire-driven environments.
Performance is assessed across varying levels of training data reduction using unseen test data. Results demonstrate that significant improvement in prediction accuracy of the PINN models could be achieved with the proposed method. The findings indicate that integrating physics-informed learning with unsupervised data compression improves sampling efficiency without compromising physical consistency.
This layered strategy represents a step toward scalable, data-efficient, physics-based surrogate models capable of complementing or accelerating CFD workflows in ventilation and fire engineering applications.
Lithium-ion batteries (LiBs) continue to proliferate through everyday activities, arguably improving our quality of life. In our ears, pockets, and bags, we routinely carry LiBs throughout the day, and, increasingly, they carry us. Fire incidents involving light electric vehicles (LEVs) (e-scooters and e-bikes, micromobility devices) on trains and in underground stations are occurring with increased frequency. For passenger trains, particularly in the underground environment, with limited options for egress and high passenger density, the potential for an onboard LEV fire to cause harm is significant. LEV fires can emit toxic and flammable gases, and, with rapid growth in heat release rate, jet flames, and possible projectiles, encourage fire spread through the train.
LEV fire risks need to be considered pragmatically by designers, owners, operators, and governments, within the context of the benefits these devices afford society, including making public transport more accessible, appealing, and valuable.
This paper reviews literature on LEVs within the underground rail context and summarises the mechanisms that cause TR, the results within the unforgiving rail context, how harm can be mitigated, and how residual LEV risks may affect the safety case for the infrastructure. Incidents involving LEVs in rail environments are discussed, assessing consequences to the infrastructure and vehicles. Design considerations to protect occupants and responders are identified.
Current operational control measures adopted globally are reviewed at high level, with commentary on the effectiveness and practicality of implementation, along with the societal value balances that must be considered. Recommendations are made for design and operation of rail infrastructure and rollingstock, and for government policy on LEV regulation and use.
Session 4A: Equipment – Part 1
Simulation-based digital twins are increasingly used to verify the control of road-tunnel ventilation systems. This paper reports two decades of experience with tunnel-ventilation-system simulators (TVSS) that reproduce aerodynamic behaviour, air quality and smoke propagation in response to real control actions. By coupling the ventilation-control software to the simulator, control strategies and emergency scenarios can be tested systematically before the physical installation is available. The paper describes the simulator, its application to control-concept verification, factory acceptance testing and staged commissioning, discusses validation, limitations and possible bias, and reflects on opportunities and risks of emerging technologies such as machine vision and AI.
Water spray systems (WSS) have long been used in Japanese road tunnels to limit fire growth and thermal damage until fire brigade arrive. Recent changes—including larger vehicle fires, multiple fire sources, electric vehicles, complex traffic conditions, and diversified ventilation strategies—require renewed assessment of their design and operation. This paper reviews conventional design concepts and operational assumptions for WSS, identifies aspects that warrant reconsideration, and highlights the need for a comprehensive re-evaluation of their appropriate application. It further discusses the fundamental performance requirements, expected effects, and desirable operational approaches for future WSS applications.
To accommodate recent increases in the required vertical clearance for expressway tunnels, securing spatial margins has become a critical challenge, necessitating the implementation of smaller jet fans. This paper presents an in-situ full-scale tunnel experiment and complementary Computational Fluid Dynamics (CFD) simulations to systematically quantify the pressure-boost characteristics of a newly developed, compact 800 mm diameter jet fan. While conventional larger models rely on established standards, the spatial interaction and aerodynamic losses of smaller-diameter fans within full-scale tunnel environments under varying air velocities and layout configurations remain poorly understood. Our field measurements successfully clarified the dependency of the pressure-boost coefficient (Kj) on tunnel wind velocities (0 to 4 m/s) and distinct installation configurations, including single-unit, in-parallel, and in-series layouts. The CFD analysis successfully validated the experimental data and extrapolated the aerodynamic behavior to higher wind velocity conditions (4 to 12 m/s). These technical findings provided a rigorous baseline for establishing generalized design factors, which were successfully integrated into the revised NEXCO Design Guideline in July 2025.
A longitudinal ventilation system employing jet fans (JFs) is utilised in many expressway tunnels in Japan. A change in legislation in 2019 reduced the space available for installing jet fans. Consequently, development began on a new 800 mm-diameter jet fan (JFT-800).
The boosting pressure generated by the JFT-800 is lower than that of conventional JF units and is susceptible to external disturbances. Consequently, a method was required to measure the boosting pressure in actual tunnels with greater speed and accuracy.
We therefore improved the conventional method of evaluating boosting pressure based on differential pressure distribution measurements and developed a new differential pressure distribution measurement system. This system involves placing measurement units—which integrate a compact differential pressure gauge and a communication device—at each differential pressure measurement point, with the differential pressure values measured by each unit being transmitted to a data-collection PC.
Using this new measurement system to measure the boosting pressure of the JFT-800 in an actual tunnel, we were able to obtain detailed results—sufficient to detect pressure fluctuations caused by air column vibrations in the tunnel—in less than one-tenth the time required by conventional methods. Furthermore, by applying time averaging to the continuously measured data, we were able to eliminate disturbances and obtain highly accurate boosting pressure values.
Session 4B: CFD / 1‑D Modelling
The aerodynamic design of high-speed rail tunnels demands accurate prediction of pressure transients, micro-pressure waves (MPW) and piston-effect airflow. This paper presents an on-going multi-resolution verification and validation framework combining analytical methods, one-dimensional compressible-flow simulation (Tools used: TETUN, NUMSTA, ThermoTun) and three-dimensional CFD (Tool used: STAR-CCM+), and quantifies, for each target quantity, which fidelity level can be trusted. A cross-level comparison for a 3-D model validated against the AeroTRAIN benchmark shows that pressure-wave amplitudes agree within a few percent at all fidelity levels, whereas raw 1-D wave-front gradients over-predict the MPW emissions by an order of magnitude; analytical estimates provide conservative brackets, and a nose-length extension of the 1-D model recovers the 3-D gradient within its calibration speed range. The framework is applied to two project studies: the Espoo–Salo high-speed line in Finland (Standards: RATO 18, UIC 779-11, EN 14067-5) and tunnels of the Czech “RS1 VRT corridor” (Standard: EN 14067-5), covering pressure transients, aural comfort and MPW emissions.
Luzern railway station, one of Switzerland’s busiest transport hubs with nearly 100,000 daily passengers, is being transformed through a new cross-rail link centred on an underground four-platform station connected to the Dreilinden and Neustadt tunnels. This paper presents the station’s emergency ventilation concept and the analytical and numerical studies used to assess its performance against defined safety objectives, focusing on smoke control and evacuation. It also evaluates the feasibility of freight train operations using a quantitative risk assessment. Key challenges include tunnel connections at both ends, extensive interconnected mezzanine areas, direct links to surface platforms, and the absence of platform screen doors. The findings provide insights into ventilation and safety design for large underground railway stations with complex operational and architectural constraints.This paper presents the emergency ventilation design for the underground station and summarizes the conceptual, analytical, and numerical studies conducted to verify the viability of the proposed system. It discusses the measures required to meet defined safety objectives and identifies optimization potential within the ventilation and smoke-management strategy.
An additional aspect under investigation is the possibility of allowing freight trains to pass through the underground station. Such operations are uncommon in Switzerland due to elevated safety risks and significant construction and operational constraints. The paper outlines the quantitative risk-analysis framework applied to evaluate this scenario.
Overall, the study provides a real-world example of the challenges associated with designing an underground station connected to tunnels at both ends, incorporating large and interlinked mezzanine halls, direct openings to above-ground platforms, and the absence of platform screen doors—conditions that together present a demanding environment for achieving stringent safety goals.
This study investigates performance of a cross-flow vertical axis wind turbine driven by piston wind generated by subway trains traveling through tunnels. Due to the high computational costs of three-dimensional Computational Fluid Dynamics (CFD) simulations, two-dimensional models are assessed as potential alternatives for preliminary design and performance evaluation. A dynamic mesh using layering technique is employed to accurately model the train’s movement within the tunnel. Simulations based on Unsteady Reynolds Averaged Navier Stokes Equations (URANS) are conducted to analyze the aerodynamic behavior, energy potential of the turbine and its possible effects on train drag. The computational results analyze furthermore the performance, accuracy, and limitations of two-dimensional approaches, aiming to identify a computationally efficient modelling strategy. The findings suggest that 2D modeling can offer valuable insights into turbine and train drag behavior with acceptable tradeoffs in accuracy.
Metro lines rely on pressure relief shafts to manage piston-effect transients on platform screen doors and providing natural fresh-air renewal. This paper presents the comfort-ventilation design study for the Toulouse Aerospace Express Metro Line 3, comparing three shaft ventilation typologies through one-dimensional SES simulation on basis of tunnel-temperature and hygienic fresh-air criteria, then ranking them via a 50-year CAPEX/OPEX comparison. The optimized configuration, based on fan freewheeling with limited peak-hour mechanical assist, proves the most cost-effective, but exposes the fans to continuous bidirectional pressure transients. Manufacturers’ feedback confirms that these transients drive the fan through aerodynamic stall and induce a measurable
DC-bus overvoltage. An anti-stall ring, regenerative variable-frequency drive, and multi-parameter condition monitoring are identified as the measures required for reliable long-term operation.
Session 5A: Smoke Control & Critical Velocity
Ensuring safe conditions for passengers during fire emergencies in above ground rail stations presents significant challenges due to the wind that influences the smoke spread. Unlike fully enclosed underground stations, open or semi open above ground environments allow natural wind to interact with buoyancy driven smoke. This interaction can redirect flow paths, disrupt smoke layering, and alter the exposure conditions faced by passengers who may remain on the platform while awaiting emergency response.
As modern transit systems increasingly adopt sustainable and energy efficient approaches, while moving toward weather protecting the above ground stations, passive ventilation strategies are becoming more pivotal to fire safety planning for above ground stations. This study investigates the extent to which wind driven airflow affects smoke movement and occupant tenability during a station fire. It also highlights certain instinctive evacuation behaviors.
To explore these issues, a set of transient CFD simulations was conducted using a representative station configuration. The model incorporated realistic fire heat release rates and examined multiple wind speeds and directions applied at the station perimeter. Key tenability indicators, including visibility, thermal exposure, and concentrations of hazardous gases, were evaluated at a typical occupant height along the platform to understand how conditions evolve under varying environmental influences.
The findings emphasize the need to incorporate wind driven smoke behavior into fire safety assessments for above ground stations, where external conditions cannot be controlled or easily predicted. Considering these effects enables engineers to better evaluate potential worst-case scenarios beyond standard code requirements, refine emergency response strategies, and identify whether architectural adjustments may be warranted to support expected passenger behavior. The study demonstrates that CFD serves as a powerful diagnostic tool for capturing complex wind–fire interactions that are otherwise difficult to predict, ultimately supporting more sustainable, resilient and informed design decisions for passenger safety in an above ground transit environment.
Fire safety during underground construction presents engineering challenges that differ fundamentally from those encountered in completed tunnels and underground facilities. Unlike operational infrastructure, construction environments evolve continuously as excavation progresses, requiring fire safety measures to adapt to changing layouts, construction activities and operational conditions. Traditional fire engineering approaches, which are generally developed for completed assets with fixed geometries and permanent safety systems, are therefore not directly applicable to large underground construction projects.
These challenges are particularly significant for major hydroelectric developments, where extensive underground tunnel networks, caverns and shafts are constructed simultaneously over several years using a combination of tunnel boring machines (TBMs) and drill-and-blast excavation. The resulting underground environment changes progressively throughout the construction programme, requiring fire hazards and emergency arrangements to be continually reassessed.
To address these challenges, a performance-based fire engineering methodology was developed for the Snowy 2.0 Hydroelectric Scheme in New South Wales, Australia. Snowy 2.0 is one of the largest pumped‑hydro infrastructure projects undertaken in Australia, comprising approximately 27 km of underground tunnels, multiple deep shafts, and a major underground Power Station Complex within Kosciuszko National Park (Figure 1).
The methodology combines systematic hazard identification, quantitative fire and evacuation analyses, and the development of engineering and operational mitigation measures to demonstrate that fire safety risks remain so far as is reasonably practicable (SFAIRP) throughout the construction programme.
Effective ventilation is critical for maintaining air quality and safety in road tunnels. This study investigates the optimization of ventilation systems in a road tunnel presenting unique architectural and operational challenges.
In this existing tunnel, induction fans—commonly used for smoke management in underground car parks—were installed at the entrance portal due to restrictions on vertical clearance within the tunnel. To accommodate these fans, the tunnel height was raised at the entrance. Computational Fluid Dynamics (CFD) simulations were employed to evaluate and optimize the configuration of the induction fans, ensuring their performance meets operational requirements. This diagnosis analysis concluded that additional jet fans were required to meet NFPA 502 critical velocity requirements. This necessitated the adjustment of the vertical clearance as well as accommodating the additional power supply and control system requirements.
This study offers practical insights into optimizing ventilation systems within architectural constraints, ensuring enhanced air quality, safety, and compliance with design standards by the means of CFD analysis. The findings contribute to the integration of engineering solutions with architectural considerations in tunnel environments.
Utility cable tunnels present a challenge for fire and life safety design due to limited prescriptive guidance, extended travel distances, and operational constraints. This paper presents a performance-based methodology for assessing means of egress within a 2400m cable tunnel in the Gulf Region.
A representative cable design fire was developed using established cable fire characterisation methods and applied within CFD modelling to determine Available Safe Egress Time (ASET). Required Safe Egress Time (RSET) was evaluated through the consideration of detection, pre-movement, and travel times. The methodology demonstrates a practical framework for evaluating life safety in utility tunnel environments.
Computational Fluid Dynamics (CFD) is widely used for detailed analysis of tunnel fire scenarios, supporting the assessment of smoke movement, hot gas temperatures, and the performance of tunnel ventilation systems. This work presents a novel fire modelling methodology for practical industrial applications, with tie-in between smoke and radiation modelling in a fast chemistry framework. The methodology has been validated against large-scale fire test data from the Memorial Fire Ventilation Test Program (MFVTP). By identifying current modelling strengths, limitations and uncertainties, this work contributes to improve the reliability and confidence in detailed 3D design analyses of tunnel fires, in particular with regards to smoke back-layering control, promoting safer design and emergency response planning.
Session 5B: Testing & Commissioning
A reduced-scale longitudinal ventilation tunnel has been constructed at Zitrón with the objective of experimentally evaluating the aerodynamic behavior of different jet-fan configurations under controlled conditions. The configurations tested include standard fans, standard fans with deflectors, slanted silencers and shaped nozzles.
The tunnel layout allows variations in fan installation height relative to the ceiling, distances between fans within the same array, blade angles of deflectors, connection-piece angles used to configure the slanted silencers, shaped nozzle geometries, fan rotational speeds, and the presence of different tunnel obstacles to simulate traffic blockage.
To characterize the flow field, pressure measurements were taken at six sections along the tunnel, complemented by air-velocity measurements, environmental conditions, and fan power consumption in each test. A dedicated electronic acquisition system was developed for the project, enabling the simultaneous and accurate recording of multiple data points during every performance evaluation. In addition, a smoke generator was employed to visualize the dynamic behavior of the airflow. The effect of traffic proved to be a significant factor in the aerodynamic response.
Future investigations will also consider alternative fan arrangements with the objective of optimizing the aerodynamic performance in the tunnel.
Tunnel fires can impair concrete linings through thermal degradation, spalling and thermally induced stresses. This study uses SAFIR to perform coupled thermo-mechanical analyses of steel fibre reinforced concrete tunnel linings under ISO 834 fire exposure, focusing on surrounding ground stiffness and lining thickness. Transient heat transfer analyses provide temperature fields for subsequent non-linear mechanical analyses with temperature-dependent material properties and thermal strains. A parametric study varies ground stiffness and lining thickness. Results show higher axial compression in stiffer ground, higher bending moments in thicker linings, and critical bending demand at intermediate heating stages rather than in the final thermal state.
Determining an accurate friction factor to be used in TVS design can be a crucial aspect of design works. Yet in the author’s experience this factor can often be crudely estimated based on previous projects without consideration of a project’s unique circumstances. The friction factor could be estimated from results of physical testing, but this is impractical during design stages. Similarly, friction factors could be attained from computation fluid dynamics (CFD) simulations, but this is generally not time or cost effective.
This paper will:
• Discuss semi-empirical methods to estimate friction factors including an assessment of skin friction and drag friction components
• Adapt and evaluate roughness assessment methodologies from the hydropower and mining industries for inclusion in semi-empirical methods.
• Detail the development of a friction factor in a recent Project of the Author, a TVS design of road tunnel with highly variable geometry.
• Review the friction factor development considering testing and commissioning results of the installed TVS.
The Auckland City Rail Link transformed Britomart Station from a terminating underground station into a through-station within a new underground rail network. This introduced aerodynamic interactions between legacy and new infrastructure and required re-evaluation of the existing ventilation systems. A staged programme of baseline airflow, and pressure testing, followed by All Systems Integration Testing, was undertaken to assess installed asset performance, validate modelling assumptions and confirm operational and emergency ventilation performance. Measured results showed good agreement with one-dimensional models once asset condition and wind effects were incorporated. The programme demonstrates the value of validating existing infrastructure prior to integration.
This paper presents a thermal assessment and full‑scale fire testing program for passive fire protection applied to steel tunnel segments. Steel segments, typically located at cross passage locations, comprise a backplate with welded stiffeners arranged in a rectangular configuration, forming enclosed pockets. Multiple passive fire protection options—including fire mortar, fire board systems and concrete infill—are evaluated with respect to their ability to satisfy specified fire‑resistance requirements.
A dedicated testing methodology was developed to quantify the influence of these protection systems on the fire performance of the steel segments. Finite Element Method (FEM) analyses were conducted to simulate the thermal response of protected segments subjected to the RABT‑ZTV (rail) fire curve, with full‑scale furnace tests undertaken to validate the numerical predictions.
The investigation includes an assessment of spalling behaviour to determine the necessity of polypropylene fibre reinforcement. Thermal gradients within the protection materials and maximum steel temperatures are analysed to verify that critical temperature thresholds associated with reductions in structural steel yield strength are not exceeded.
The outcome of this study establishes a framework for the selection, evaluation and experimental validation of passive fire protection systems for steel tunnel segments.
Session 6A: Equipment – Part 2
Jet fan installation efficiency can degrade significantly as tunnel physical condition changes over time, particularly where new equipment or structural elements are installed close to fan outlets. This paper presents a road tunnel case study using in-tunnel testing and CFD to identify, quantify and mitigate installation losses. The case study presented assesses degraded installed performance in an ageing road tunnel and investigates scoop-style deflectors to recover thrust transfer. The paper shows an example of the extent of installation performance degradation and how the losses may be mitigated to maintain the ventilation system performance.
Over the past 15 years, variable-speed controlled jet fans in road tunnels have gradually but steadily become popular in Japan, because of the benefits of energy saving in normal operation and improved safety in incident response. The energy saving principle detailed by Bopp [1] more than three decades ago [1] was expanded upon by Nakahori et al [2]. The proposed paper will present 3D simulations that give more information than those early 1D studies, enabling better understanding of the dependence of jet fan efficiencies on their speeds of rotation. The authors are not aware of any such previous 3D study even though various excellent studies have enhanced understanding of jet fan operation at full speed in demanding applications – e.g. Kato et al [3].
The paper is primarily concerned with energy saving and presents a series of 3D CFD analyses using the software CONVERGE. In the simulations, jet fans exist at both ends of a tunnel and are operated in opposing directions. At one end, a single fan operates at a fixed rotational speed, usually 100%. At the other end, two or more fans operate at reduced speed. Attention is focussed on cases in which the net flowrate midway between the two sets of fans is zero. In this condition, the opposing thrusts are equal and the required powers can be compared meaningfully. As shown by Kato et al [3], the performance of fans operating against imposed counter-forces can differ from that in the absence of such forces, so all of the fans are operating in a realistic environment in which conventional 1D analyses can be misleading. The paper will include comparisons of the inferred power requirements with corresponding predictions using 1D representations. Comparisons will also be made with measurements of energy consumption characteristics measured in full-scale tests in the past. Overall, the paper will strengthen understanding and will contribute to international recognition of the potential energy-saving benefits for tunnel owners and for the planet.
[1] R Bopp (1994) “Energy-optimized ventilation of road tunnels by speed control of jet fans”, Proc 1st int conf on Tunnel Control and Ventilation, ITC Ltd, 219-229.
[2] I Nakahori, T Ato, K Murakami, D Araki, T Kanatani, A Vardy (2009) “The use of inverter-driven jet-fans to reduce tunnel ventilation costs”, 13th ISAVVT, BHR Group, 69-80.
[3] N Kato, S Ito, A Mizuno, T Chihara & S Hashimoto (2019) “Boosting pressure generated by jet fans when operated against the longitudinal airflow in road tunnels, 18th ISAVFT, BHR Group, 499-511.
A methodology for rigorous evaluation and verification of primary jet fan operational parameters, based on the application of Newton’s laws in thermo-mechanical Open Systems, was proposed at the previous ISAVFT symposium. The comprehensive evaluation of pressure and shear forces together with interface momentums provided direct access to in-situ Thrust and Overall Installed Efficiency in tunnel ventilation design solutions. This approach removed the uncertainties in design analysis for such fundamental jet fan operation parameters.
As part of the development of this methodology, a more accurate and individual quantification of jet fan efficiency parameters for Off-Loading and Installation Efficiency (or Eccentricity Coefficient) is explored in this work. This has been investigated by application of the jet fan in-situ thrust model in conjunction with an explicit 3D jet fan representation including the rotating fan blades, which allows for a direct and separate/ individual quantification of the stated jet fan efficiency parameters from the design analyses.
Additionally, with the application of the approach to engineering design tasks, the impacts of encountered flow instabilities in design applications, on the accuracy of analysis solutions is explored and discussed from project experience.
The increasing complexity of tunnel ventilation systems, combined with rising expectations for safety, resilience and sustainability, is accelerating the adoption of digital monitoring and analytics throughout the tunnel lifecycle. This paper presents a real-world case study from the A55 Conwy road tunnel in Wales, where a severe vehicle fire in June 2025 provided a full-scale test of emergency ventilation performance and digital asset intelligence capabilities.
During the incident, a truck-mounted crane caught fire within the westbound bore, generating extreme thermal and smoke conditions. Seventy-two jet fans were automatically activated within one minute of detection, enabling safe evacuation and effective smoke clearance prior to the arrival of emergency services. In parallel, real-time data from a cloud-connected monitoring platform provided continuous visibility of fan operation, temperatures and vibration behaviour throughout the event.
Post-incident analysis combined time-series data, thermal and vibration shock metrics, exposure analysis, and frequency-domain spectral techniques to assess potential degradation mechanisms arising from thermal shock and sustained operation under fire conditions. Comparative analysis between eastbound and westbound fans enabled prioritisation of inspection and maintenance activities, while statistical evaluation of spectral changes highlighted emerging risks such as mechanical looseness, misalignment or thermally induced shaft deformation.
The paper demonstrates how digital monitoring during operation can extend beyond compliance verification, supporting evidence-based decision-making during emergency response, accelerating safe recommissioning, and reducing unnecessary asset replacement. Lessons learned from the Conwy Tunnel incident are discussed in the context of smart tunnels, predictive maintenance, and performance-based fire safety management, offering practical guidance for operators and designers seeking to improve resilience and lifecycle value in tunnel ventilation systems.
Session 6B: Platform Screen Doors
Smoke confinement in underground metro stations requires the determination of a minimum extraction flow rate to prevent smoke spread beyond a containment screen. CFD simulations were performed for platform lengths from 16 to 64 m and fire sizes ranging from 0.1 to 10 MW. The numerical results were first compared with an existing analytical model, which provided satisfactory first-order predictions of the confinement flow rate. A semi-empirical correlation was then developed to better represent the physical mechanisms governing confinement, incorporating the effects of fire size, station geometry and air supply area. Validation against additional CFD simulations demonstrated improved predictive capability. The proposed model provides a practical and conservative tool for the preliminary design of smoke control systems in underground metro stations.
This study presents the post-construction evaluation of an as-built Tunnel Ventilation System (TVS) for a short, but relatively complex metro tunnel. The assessment combined design reviews, extensive site measurements, and numerical modelling to evaluate airflow performance with critical velocity calculations and smoke confinement under fire emergency conditions. The assessment incorporated and compared three one-dimensional models (SES (1), IDA Tunnel(2), and CONTAM (3)) and two computational fluid dynamics (CFD) software (FDS (4)(5)(6) and OpenFOAM (7)) to investigate airflow behaviour in certain complex geometric areas.
Field testing included general tunnel airflow measurements, annular velocity around trains, station pressure differentials with platform screen doors (PSDs), individual fan performance testing, and smoke testing and visualizations. Particular focus was placed on the influence of the PSDs, which were found to affect airflow distribution between stations and tunnels differently as a function of the tunnel overall system resistance for different fire locations. The study demonstrates how holistic field testing and data collection can support system verification and optimization post-design.
Session 7: High Speed Rail Tunnels
The present study conducted field tests in a 6.1 km long railway tunnel to investigate the aerodynamic effect. Measurements denote pressure peaks are not sensitive to the measuring location. At 350 km/h, waveforms of initial compression wave are progressively distorted due to the non-linear steepness and finally triggers a sonic boom within the tunnel. The minimum pressure gradient to induce a sonic boom is about 18.34 kPa/s. The maximum value of A-weighted sound pressure level of the sonic boom is about 100 dBA while it is only 94.25 dBA at 20 m from the tunnel exit.
Tunnel internal structures are an important part of a highly complex system that makes transport tunnels function appropriately. structures include architectural panels, traffic signs, fire walls, cameras, etc. Often these systems are repeatable and replicated along the longitudinal length of the tunnel providing opportunity for detailed engineering assessments to deliver significant costs Capex and Opex savings when the loads are analysed and estimated to a high level of confidence. This paper looks at how the industry currently estimates the vehicle induced loadings on tunnel internal structures and services. The vehicle-induced aerodynamic pressure is investigated by numerical and theoretical methods. The methods are validated against experimental data. A sensitivity study of the vehicle-induced aerodynamic pressure to the main design parameters like vehicle velocity, blockage ratio, tunnel cross section shape, vehicles’ arrangement is finally presented and a formula for estimation of pressure loads in a variety of arrangements is proposed.
Session 8: Digitalisation
Modern underground rail networks, such as the Doha Metro, require tunnel ventilation systems (TVS) to operate with high precision and minimal human intervention to maintain passenger safety and comfort. This paper presents a case study on integrating the TVS with the Supervisory Control and Data Acquisition (SCADA) system, focusing on how automation can minimize manual operations. For control room operators, managing rapid transitions between normal, congestion, maintenance, and emergency modes under high-pressure scenarios presents a significant cognitive challenge. Selecting the optimal evacuation route during a tunnel incident is challenging. This study demonstrates how automated logic supports the operator in complex mode transitions and assists operators in critical decision-making tasks. Furthermore, this paper outline the overall interface between the SCADA system and the TVS, the criteria for switching between various operational states (fully automatic, semi-automatic, or manual), and SCADA-layer interface with the signaling system (SIG) that ensures a synchronized response across the entire network, signaling system response is following a predefined Rescue Operation Plan and operational SOPs.
“Metro Madrid’s digital twin fuses real-time sensor data with SES normal-operation simulations; real data reflect actual tunnel conditions, while SES simulations predict airflow and heat behavior—together enabling smart, predictive ventilation control.”
Metro de Madrid has developed GIV (Gestor Inteligente de Ventilación), an advanced digital twin platform that integrates real operational data with SES (Subway Environment Simulation) modeling to manage and optimize tunnel ventilation system’s energy consumption. This system represents a breakthrough in real-time predictive ventilation management for large underground transport networks.
The operational layer of GIV continuously ingests real data from the metro environment, including CO₂ concentration, temperature, humidity, air velocity, pressure, fan and damper positions, energy consumption, and train positions—capturing the dynamic piston effect of moving trains and ambient outdoor conditions. This ensures the digital twin remains synchronized with the tunnel’s current state.
Complementing this, the predictive layer employs SES simulations, to calculate airflow, heat balance, fan performance, and tunnel–station interactions. SES offers rapid results for forecasting short-term airflow behavior, testing ventilation control strategies, and assessing energy-saving opportunities.
The fusion of live sensor data and SES simulated behavior produces a true digital twin —an evolving, data-driven model that both mirrors and anticipates system conditions. This enables GIV to forecast air quality trends, proactively recommend ventilation settings, detect operational anomalies, and optimize energy distribution.
Operating on a continuous learning and adaptation cycle using Artificial Bee Colony Technique (ABC), GIV updates system’s control every eight hours based on updated inputs. Through this dynamic synergy of perception, prediction, and control, “Metro Madrid” has achieved a ventilation management system that enhances passenger comfort, energy efficiency, and operational resilience across its extensive underground network (350 stations and tunnels) reducing 40% energy consumption. The GIV started in 2017, however it has been in continuous improvement, since then.
Session 9: Road Tunnel Refurbishments
This paper presents the refurbishment of the 2.8 km Rokko Mountain Tunnel in Japan from a semi-transverse ventilation system to a longitudinal ventilation system using variable-speed jet fans and existing ventilation shafts. The change is a response to the collapse of the suspended ceiling in the Sasago Tunnel in 2012. The upgraded system improves structural safety and has achieved significant energy savings during normal operation by operating multiple jet fans at low speed. During fire emergencies, the longitudinal airflow is reduced to below 2 m/s within 90 seconds and achieves near zero-velocity conditions within approximately 3 minutes, and operational results have confirmed the effectiveness of the ventilation strategy. However, condensation near tunnel portals has emerged as a new challenge.
Retrofitting smoke exhaust systems in operational underground concourses requires life safety upgrades to be balanced with constructability and service continuity. This paper presents a performance-based retrofit of an existing smoke extraction system serving a subsurface public concourse connected to tunnels and adjacent underground spaces. Key transferable lessons include early validation of stack-effect conditions, reuse of existing ventilation infrastructure where spatial constraints limit new ductwork, phased impairment planning, integrated controls testing, and commissioning methods that confirm installed performance against modeled assumptions. These principles can inform resilient ventilation upgrades in other complex underground concourse environments.
Nordhavnsvej Tunnel (NHV), a 700 m twin-tube road tunnel commissioned in 2018, is now being extended by 1,400 m into the Nordhavn Tunnel (NHT). When the original NHV design was developed, low pressure water mist (LPWM) technology was still in an early stage of adoption, supported by limited full scale testing and with a recommended design density of 2.5 L/min/m² for road tunnel applications. Over the past decade, the water mist industry has matured significantly, with extensive fire testing programmes, improved performance evidence, and updated international standards.
The paper focuses on the following major design and integration challenges that shaped the final solution for the fixed fire-fighting system (FFFS).
The design integrated the new LPWM system for NHT (4 L/min/m²) with the existing NHV LPWM installation (2.5 L/min/m²) while maintaining full hydraulic compatibility. Only the main pumps at the existing pump station were replaced, with all remaining system components retained and adapted to support higher‑density operation.
A six‑zone activation philosophy was developed to address the wider ramp areas, enabling larger‑area coverage and improving fire‑service accessibility during an incident.
The water‑mist ring main was installed beneath the tunnel road slab using PE‑100 pipework with integrated leakage detection. This approach reduced material footprint, preserved space at the tunnel crown for future upgrades, and maintained system resilience through a looped configuration.
The existing pump station (NHV) at the portal could not serve the new integrated tunnel due to the extended length, therefore, the entire pump west pump station needed to be refurbished with the diesel pumps replaced with electric pumps. Further, a new pump station needed to be installed at the new extended tunnel portal towards the east. Together, the two pump stations operate in a duty–standby arrangement, providing redundancy, enabling future tunnel extensions, and allowing removal of the existing diesel pumps.
This paper presents the engineering approach, integration strategy, and key design decisions adopted to extend and integrate the existing and new fire protection systems.
Tunnel fires expose reinforced concrete linings to extreme thermal conditions that can cause severe material degradation, explosive spalling and substantial reductions in structural capacity. This study evaluates the thermal and economic performance of passive fire protection applied to concrete tunnel structures subjected to severe hydrocarbon fire scenarios. Validated finite element analyses, accredited fire testing and published research are used to compare unprotected concrete with linings protected using calcium silicate boards under RWS, RABT-ZTV and HCM exposure. Results show that passive protection limits heat penetration, preserves residual structural performance and reduces post-fire rehabilitation, improving tunnel resilience and whole-life asset cost.
