Numerical simulation of different HGV fire scenarios in curved bi-directional road tunnels and safety evaluation Ciro Caliendo a,⇑ , Paolo Ciambelli b , Maria Luisa De Guglielmo a , Maria Grazia Meo b , Paola Russo b a Department of Civil Engineering, University of Salerno, 84084 Fisciano (SA), Italy b Department of Industrial Engineering, University of Salerno, 84084 Fisciano (SA), Italy article info Article history: Received 29 August 2011 Received in revised form 15 February 2012 Accepted 2 April 2012 Available online 13 May 2012 Keywords: Curved bi-directional road tunnels Fire scenarios Heavy good vehicle Traffic flow Jet fans CFD modelling abstract A CFD modelling is presented for simulating the effects of fire in curved bi-directional road tunnels. A fire source due to a heavy goods vehicle (HGV) with a peak of the heat release rate (HRR) of 50 MW is sim- ulated. The influence of position of the HGV fire in the tunnel, tunnel geometry, longitudinal ventilation of jet-fans, and the presence of traffic flow, are more especially investigated. The effects of these variables on hot gas temperatures, air flow velocity, visibility distance, toxic gases concentrations, and the people evacuation process, are shown. The worst fire scenario was identified to be when the HGV was located in the middle of the tunnel length and in the driving lane centre. This was due to the combined effect of ventilation and geometrical characteristics. The presence of traffic, in contrast with the isolated HGV, caused higher temperatures, interfered with the air flow by decreasing its velocity, and decreased more rapidly the visibility distance in the tunnel. However, toxic gases were found to be below the minimum values that may represent a potential danger to human life. People evacuation from the tunnel was found to be safe when the time before starting to walk is short and the walking speed is a rather high. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction The catastrophic tunnel fires occurring in Europe over the last few years (Mont Blanc tunnel between France and Italy in 1999 with 39 depths, Tauern tunnel in Austria in 1999 with 12 depths, Saint Gotthard tunnel between Switzerland and Italy in 2001 with 11 depths) have led the public opinion, competent authorities, and the international research community, to become much more in- volved in the safety of people who use these structures and in pre- venting tunnels from collapsing under very high temperatures due to fire. These tunnels are characterised for their passing through the mountain chain of the Alps for a very long distance (the Mont Blanc tunnel is 16.6 km long, Tauern tunnel is 6.4 km long, while the Saint Gotthard tunnel is 16.92 km long) with bi-directional traffic. The above-mentioned high toll of human lives, as well as the costs for repairing the structures and indirect costs associated with the temporary closure of the roads containing these tunnels, have been the main reasons for the development of research pro- jects, recommendations and actions for reinforcing safety in road tunnels (Safe tunnel, 2004; Safe T, 2006; European Directive, 2004; UPTUN, 2008; United Nations, 2010). Tunnel fires, however, are very complex phenomena because of the mutual interactions between physical and chemical processes (turbulence, combustion, radiation, etc.) which control fire and smoke development in a closed space. Among approaches for studying and analysing tunnel fires the following are more espe- cially considered: full-scale experiments could provide the most useful data but they are expensive, sometimes dangerous and re- quire a long time for their setting up; reduced-scale experiments are often not able to reproduce full-scale features; computer sim- ulations have nowadays become an ever more common practice for showing fire behaviour and quantifying impacts. Computer simulations give the following advantages: (i) evaluating fire behaviour more efficiently since many detailed data, which are unattainable by any of the two other approaches, are used and more quickly; (ii) reasonable cost of calculation compared to real or reduced-scale tests are expected; (iii) understanding better the relationships between the fire and the high temperatures and/or toxic gases generated, as well as the visibility conditions for evac- uation; (iv) taking better account of the tunnel geometry, traffic characteristics, type of vehicle, location of fire, and dangerous goods circulation. These goals are expected to be achieved, in par- ticular, by computational fluid dynamic (CFD) models. CFD models and associated code tools lead to dividing the tunnel volume into small cells inside which the fundamental equations of fluid dynamics are solved by using the finite volumes method. Espe- cially CFD analysis permits solving the fundamental equations of conservation (energy, mass, species, momentum) coupled with sub-models to describe the complex process of turbulence, 0886-7798/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tust.2012.04.004 ⇑ Corresponding author. Tel.: +39 89 964140; fax: +39 89 964045. E-mail address: ccaliendo@unisa.it (C. Caliendo). Tunnelling and Underground Space Technology 31 (2012) 33–50 Contents lists available at SciVerse ScienceDirect Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust