This paper develops a novel modelling approach for ventilation flow in tunnels at ambient conditions (i.e. cold flow). The complexity of full CFD models of low in tunnels or the inaccuracies of simplistic assumptions are avoided by efficiently combining a simple, mono-dimensional approach to model tunnel regions where the flow is fully developed, with detailed CFD solutions where flow conditions require 3D resolution. This multiscale method has not previously been applied to tunnel flows. The low computational cost of this method is of great value when hundreds of possible ventilation scenarios need to be studied. The multi-scale approach is able to provide detailed local flow conditions, where required, with a significant reduction in the overall computational time. The coupling procedures and the numerical error induced by this new approach are studied and discussed. The paper describes a comparison between numerical results and experimental data recorded within a real tunnel underlining how the developed methodology can be used as a valid design tool for any tunnel ventilation system. This work sets the foundations for the coupling of fire-induced flows and ventilation systems where further complexities are introduced by the hot gas plume and smoke stratification.

The capabilities of the ventilation systems in the two road tunnels at Dartford (UK) are analysed using a multi-scale modelling approach. Both tunnels have complex semi-transverse ventilation systems with jet fans to control longitudinal flow. The construction and ventilation systems in the tunnels are described and the current emergency ventilation strategies are presented. The analysis includes a coupling of a 1D network model with 3D components, representing the operational jet fans, built using computational fluid dynamics. The jet fans were experimentally characterized on-site and the findings were compared to the model predictions. The predicted ventilation flows for each of the emergency ventilation strategies are presented and discussed. In cold-flow conditions, ventilation velocities significantly above 3 m/s can be generated throughout the tunnels. However, it is observed that 1/3 of the flow generated in the East tunnel is diverted from the tunnel up the extract shafts. The model was used to simulate various reduced fan combinations and thus the level of redundancy in each of the systems has been estimated. It is found that an acceptable level of ventilation may be produced in the West tunnel, even if several pairs of jet fans are disabled. In the East tunnel there is less redundancy, but an acceptable level of ventilation control can be maintained with one or two jet fans disabled.

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The University of Edinburgh and its alumni have made significant contributions to knowledge in the field of tunnel fire safety engineering. This paper summarises the situation of tunnel fire safety in the early 1970s, when the department of fire engineering was founded and briefly discusses all the contributions to knowledge in the field, made by Edinburgh and its alumni in the past four decades. Research carried out at Edinburgh has changed the way the tunnel safety industry estimates heat release rates in tunnels, has influenced way design fires are specified and has challenged industry opinion about the use of water sprays in tunnels. This paper is part of a celebration of four decades of fire research at Edinburgh.

The results and findings of three previous research projects are combined with new research to estimate the overall influence of longitudinal ventilation on fire size and spread in tunnels. Each of the three previous projects is briefly described. Combining the results of these three projects, together with knowledge of HGV fire behaviour in an experimental test, enables the estimation of the maximum fire size of a fire in a tunnel and the conditions under which it might spread to an adjacent vehicle, for a given longitudinal ventilation velocity.These results have been combined into a single computer model. Results are presented and discussed. It is concluded that, although it may greatly increase the heat release rate of a fire in a tunnel, increasing the ventilation velocity will tend to reduce the likelihood of the fire spreading to an adjacent vehicle, assuming no flame impingement.

In a number of catastrophic tunnel fire incidents, the fire has often spread from vehicle to vehicle over large distances, occasionally hundreds of metres. Five possible means of fire spread are briefly discussed. The paper focuses on fire spread by flame impingement and investigates the conditions under which flame impingement will occur on a 4 m high HGV downstream of the initial fire. The study uses Bayesian methods to predict the probability of impingement at distances from 0 to 20 m downstream, based on experimental tunnel fire data. The influence of tunnel size, ventilation velocity and vehicle separation on the probability of impingement are discussed. In general it is shown that impingement on a downstream HGV is more likely in a smaller tunnel with a higher ventilation velocity. It is suggested that flames from a HGV fire in a tunnel will almost certainly impinge on a downstream HGV at distances of up to 20 m, and possibly much greater distances.

In this paper, the effects of geometric skewness and abutment restraint on the fire resistance of a real highway bridge have been studied. Four finite element models have been investigated using rectangular and skew shapes with and without modelling the abutment. The investigation has been carried out in three steps: 1) heat transfer analysis under a specified hydrocarbon fire; 2) simulation of the thermo-mechanical response of the bridge superstructure over the entire duration of the fire using beam and shell elements to represent the structural components; 3) detailed processing and interpretation of the simulation results to understand and illustrate the global response of the structure by comparing all the models. Results indicate that a skew bridge may possess greater inherent resistance to fire. For the two-span highway bridge model, restraint from the abutment does not affect the estimated failure time significantly.

This paper presents the results of a series of reduced scale experiments to investigate the temperature conditions leading to backdraught in a fire compartment (0.8m x 0.4m x 0.4m), using solid polypropylene pellets as the fuel. The factors of primary interest are the pre-burn time, before the fire becomes oxygen limited, the duration of door closure, and the temperature distribution in the compartment. It is shown that the temperature inside the compartment is crucial for the occurrence of backdraught. Above 350°C, backdraught by auto-ignition is possible. If a pilot spark is present, backdraught may occur at temperatures down to 300°C. It is shown that backdraught conditions can be achieved in the early stages of a fire as long as a suitable temperature is reached, at considerably lower temperatures than those generated during flashover. Further investigation on gas concentration is essential to understand the chemistry of backdraught combustion.