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Tunnel safety, risk assessment and decision-making
Tunnelling and Underground Space Technology 25 (2010) 91–94
Contents lists available at ScienceDirect
Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust
Technical note
Tunnel safety, risk assessment and decision-making Alan N. Beard * Civil Engineering Section, School of the Built Environment, Heriot-Watt University, Edinburgh, Scotland EH14 4AS, United Kingdom
a r t i c l e
i n f o
Article history: Received 30 July 2008 Received in revised form 15 July 2009 Accepted 15 July 2009 Available online 18 September 2009 Keywords: Tunnel safety Risk assessment Decision-making
a b s t r a c t This article gives a brief account of a project which was commissioned by the European Parliament and which has resulted in a report which has been published and is available on the web-site of the European Parliament [Beard, A.N., Cope, D., 2008. Assessment of the Safety of Tunnels. Commissioned by the European Parliament; Report IP/A/STOA/FWC/2005-28/SC22/29. Published in February 2008 on the European Parliament web-site under the rubric ‘Science and Technology Options Assessment’ (STOA)]. The project was funded by a grant from the European Parliament. The author was requested to carry out a study of tunnel safety and make recommendations to be considered for possible application within the European Union. The background to the project was the large number of catastrophic tunnel fires which have taken place in Europe since 1995. Twenty five recommendations are made within the Report the purpose of which is to help to increase tunnel safety in the European Union and, primarily, to help to move towards a common system of tunnel safety decision-making and risk assessment. This article focuses on some aspects of the content. However, it should not be assumed that aspects which are not included here are of lesser importance. Ó 2009 Published by Elsevier Ltd.
1. Introduction This article gives a very brief account of a ten-month project which resulted from the European Parliament requesting the author to conduct a study on tunnel safety. The focus of the study is on the process of decision-making and risk assessment rather than specific factors affecting tunnel risk, although some specific factors which have emerged have been included in the Report. The intention was to make recommendations for consideration by the European Parliament with a view to possible implementation. The approach taken has been wide-ranging; both road and rail tunnels are included. Categories not included are: (a) tunnels under construction, (b) malicious acts, and (c) underground railway/metro systems. Although these categories were nominally not included mention has been made of them to some extent. Over the last 15 years there has been a great increase in the building of both road and rail tunnels, world-wide. In particular, in some countries the rate of tunnel construction has been rapid. For example, before 1995 Shanghai did not have a metro system. By the end of 2007 it had eight lines with a total length of 227 km and 161 stations, although not all the system is underground. More lines are under construction in Shanghai. Globally, not only are many tunnels being constructed but the length and complexity of tunnel systems is increasing and tunnels are forming parts of complex systems; for example, the Oresund link between Sweden and Den* Tel.: +44 131 451 4414; fax: +44 131 451 4617. E-mail address: [email protected] 0886-7798/$ - see front matter Ó 2009 Published by Elsevier Ltd. doi:10.1016/j.tust.2009.07.006
mark includes a bridge and a tunnel. Also, it has been stated that the Gotthard Base Tunnel, currently being constructed in Switzerland, will, at 57 km, be the longest tunnel in the world (Kauer, 2001). The construction of the Channel Tunnel between France and England stimulated both theoretical and experimental research work. Unfortunately this did not prevent a very serious fire taking place in the Channel Tunnel about 2 years after opening. Luckily there was no loss of life in that fire, although the story may have been very different if the fire had started close to the amenity coach in which the heavy goods vehicle (HGV) drivers had been travelling and not close to the other end of the train, as actually happened. Probably the most serious underground fire to date took place in the Baku underground railway metro system in Azerbaijan on 28th October 1995. In that fire approximately 300 people lost their lives. Since then there have been several other serious fires in tunnels, including the fires at Mont Blanc, Tauern, St Gotthard and Kaprun, right up to the Viamala Tunnel fire, Switzerland (2006), which killed nine people. Also, there is the Burnley Road Tunnel fire, Melbourne (2007), in which three people died from the initial crash and the Santa Clarita Road Tunnel fire in California (2007) in which three died. Overall, there has been a significant increase in serious tunnel fires over the last 15 years, resulting in many fatalities. This is probably related to the considerable increase in traffic over these years and especially the great increase in HGV traffic passing through tunnels. Simultaneously, over the last 15 years, there has been an increase in the use of risk assessment techniques although there
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has been no uniformity as to what this should involve. Also, an initiative aimed at furthering the use of risk assessment techniques in tunnel construction has come from major insurance companies such as Swiss Re and Allianz AG and a document has been prepared under the aegis of The International Tunnelling Insurance Group (International Tunnelling Insurance Group, 2006), which is expected to have a major impact on tunnel projects (Dix, 2004a). It may have an effect on design and operation as well. If the Code is not met during construction then insurers may withdraw cover and without insurance projects would not be able to continue. In this overall context the European Parliament commissioned a study aimed at improving tunnel safety and assisting in moving towards an acceptable, common, system of decision-making and risk assessment in the European Union. The final Report has been placed on the European Parliament’s web-site under the aegis of the ‘Science & Technology Options Assessment’, i.e. (STOA) initiative.
Fig. 1. Road tunnels: numbers of fatalities in fires world-wide (1987–2006), by vehicle involvement. Total = 96 (Not inc. during construction or malicious.) Ó A.N.Beard.
involving HGVs, see Fig. 1. It would be desirable to reverse the trend for more and more freight to be transported by road rather than rail; in Western Europe the rail share is around 8%, down from about 21% in 1970.
2. The areas covered The main topics included in the Report are: (a) Setting the scene: an overall description of the present position; (b) Tunnel design and risk assessment: this is the largest section considering prescriptive requirements and risk assessment, modelling, qualitative and quantitative aspects, criteria for acceptability of risk and safety management. This section also considers the need for an extensive and continually up-dated knowledge base; (c) Regulatory initiatives, including the EU Directive of 2004 (EU Directive document 2004/54/EC, 2004); (d) Other influences on tunnel safety, e.g. global warming; (e) Particular tunnel cases: a brief account of some specific tunnel projects; (f) Strategic and specific issues; (g) Recommendations, of which there are 25.
3. Key points from the Report The Report considers both road and rail tunnels, with an emphasis on road tunnels. It is pointed out that, although historically the risk has been less in rail tunnels than in road tunnels, the rail tunnel stock in Europe is very old and many have very poor fire-fighting and escape features. In 1998 the risk, historically, may have been regarded as relatively low in road tunnels but since that date we have seen many disastrous road tunnel fires. It is necessary to look at the system itself and to consider changes to systems, such as traffic volumes and vehicle types, rather than be mesmerized by historical statistics. Systems change and it is essential to be aware of that and try to take account of it. In the following a few points only are mentioned, to give a flavour of the content of the Report. This does not mean that topics which are not mentioned are of lesser importance. For more details and references, see Beard and Cope (2008). 3.1. Setting the scene It appears to be the case that, overall, most deaths in tunnel incidents result from common traffic accidents (about two-thirds) and it is essential to address this as well as fire-related incidents which are more likely to result in multiple fatalities. Fatalities in road tunnel fires are strongly associated with heavy goods vehicles (HGVs); approximately 71% of fatalities in tunnel fires are in fires
3.2. Tunnel design and risk assessment Quantitative risk assessment is coming to be used as part of tunnel safety decision-making and this may or may not be a desirable development depending upon how it is carried out. The use of quantitative risk assessment has the potential for leading to unacceptable designs. It is necessary to adopt a broad perspective and be aware of the possible pitfalls of risk assessment. Risk assessment is not a panacea; it is a tool and, like all tools, it may be inappropriate for a task or used badly. Overall, a new tunnel may be designed, or an existing tunnel up-graded, through the use of prescriptive regulations, qualitative risk assessment or quantitative risk assessment; or a mixture of these. Beyond that, quantitative risk assessment may then be composed of deterministic risk assessment (i.e. using deterministic models, e.g. computational fluid dynamics models or zone models) or non-deterministic risk assessment (e.g. using models such as fault trees, stochastic models or points schemes such as EUROTAP (EUROTAP, 2006)); or a mixture of the two. Results from physical models may also be used, for example in the form of small-scale or large-scale tests. Many more large-scale tests are necessary in addition to small-scale (Johnson, 1991; Beard, 1992); and on a continual basis because ‘the system’ is continually changing. Carrying out large-scale tests is expensive, but vital in order to inform the knowledge base which under-pins decision-making in general and risk assessment in particular. When shifting to an approach which includes risk assessment the following questions arise: (a) which methodology should be used in order to conduct a risk assessment? What are to be the criteria for acceptability of a methodology? (b) Which models should be employed, and how, to assess the risk and make a decision? What are to be the criteria for acceptability of a model and how it is used? (c) What are to be the criteria for acceptability of risk?; this is basically an ethical decision, not a technical one, as such the criteria need to be generally acceptable to the public. Further, to support the above a comprehensive knowledge and understanding of the system is needed; i.e. a ‘knowledge base’ needs to be in existence and continually up-dated. This means there is a need for both theoretical and experimental research and gathering of information/data; this needs to be on a continual basis because the real world system, and its values, changes all the time. The Report argues for the establishment of a ‘One Stop Shop’ for the European Union which would act as a centre for the comprehensive gathering of information, e.g. statistical data on tunnel safety, as well as information about what research has been done
A.N. Beard / Tunnelling and Underground Space Technology 25 (2010) 91–94
and what is under-way. Such a ‘Shop’ would serve as a very valuable resource for all those conducting tunnel safety risk assessments, as well as being available to other interested parties, e.g. operators, emergency services, regulators and other concerned people. The Report goes on to consider problems with using theoretical models as part of fire safety decision-making. It is often stated in the literature that a model has been ‘validated’ and the implication is that the model has been ‘proven correct’. It is, however, impossible to prove a model to be ‘correct’. An example of the kinds of problems involved is illustrated in a recent ‘round-robin’ exercise (Rein et al., 2007) in which eight groups used the same computational dynamics (CFD) model to predict the values of variables such as temperature expected in an experimental test. The comparisons were carried out on an a priori basis; i.e. the users had effectively not ‘seen’ or used any of the results from the experiment (Beard, 2000). As a general rule, the predictions were not at all good. There was generally a wide scatter amongst the predictions by users and, also, predictions usually compared poorly with experimental results. Although this study relates to a non-tunnel case the general conclusions would certainly be expected to pertain to tunnels as well. It is pointed out that the testing of models is problematic and has been discussed in Beard (2005a,b). In principle, results from deterministic models can be compared with experiment; however, how the comparison is carried out is very important (Beard, 2005a,b). Also, it must be realized that experimental data are not necessarily ‘hard and fast’ but are subject to, for example, uncontrolled variables. Even experiments which are intended to replicate earlier experiments and should, in principle, produce identical results may not do so and the differences between results from ‘identical’ experiments may be considerable, see Beard (2005a,b). Comparison between theory and experiment is not a straight forward process and different kinds of comparisons need to be carried out (Beard, 2005a,b). Probabilistic models cannot be directly compared with experiment and testing is more problematic. The only real test for a probabilistic model of a system is to compare with historical statistical data for the system of concern. In that case it would be extremely important to ensure that the model’s results and the historical data were at the same abstraction level; see Beard (2005a,b). Not comparing at the same abstraction level, i.e. ‘like with like’, is one of the sins of statistical analysis and one way of ‘lying with statistics’ (Beard, 2005a,b). A regulatory framework needs to be created so that models, especially computer-based models, may become generally acceptable as part of safety decision-making. In general, what is required is: [1] A model which has the potential to be valuable for decisionmaking in a specific case; in general more than one model may be used in a given case. [2] A ‘Methodology of Use’, which is generally acceptable and encourages a user to be comprehensive and explicit. [3] A ‘Knowledgeable User’, who is capable of employing an acceptable ‘methodology of use’ in a comprehensive and explicit manner to a model which has the potential to be valuable in a specific case, and of interpreting results justifiably. Concerning criteria for acceptance of risk, the Report points out that, internationally, different criteria have been used and there is a need for coherence. It is mentioned that the Norwegian Government has adopted a ‘Vision Zero’ policy which aims to reduce road deaths steadily year by year (Norwegian Public Roads Administra-
93
tion, 2006). Sweden and Denmark also have ‘Vision Zero’ policies. Reducing road traffic accidents in general would include road traffic accidents in tunnels. Whilst reducing the probability of fatalities to zero is not realistic, as a guiding vision it may be regarded as extremely valuable, as long as it is genuinely acted upon year by year. Whether or not such a policy should be adopted across the European Union needs to be decided. If such a policy were to be accepted it would need to be ensured that real changes were taking place, year by year, ‘on the ground’ and that the policy did not exist largely on paper only. The fact that ‘the system changes’ would need to be taken into account. For example, there has been a considerable change in traffic patterns related to tunnels over the last 40 years with far more HGVs amongst other changes. Gradual changes in the system like this need to be consciously looked for and not allowed to ‘creep up’ on us. A research effort aimed at gauging current and future changes needs to take place. This would have an input to the ‘One Stop Shop’ mentioned above. Safety management is considered briefly in the Report and the need for such systems to be as ‘systemic’ as possible (Santos-Reyes and Beard, 2005). Also considered is the great need for a knowledge base which would be continually up-dated and supported by both theoretical and experimental research. Some of the tunnel research projects which have been conducted over the last few years, largely funded by the European Union, are described very briefly. Concerning regulation, the EU Directive of 2004 on minimum requirements for tunnels in the Trans-European Road Network is discussed to some extent. The Directive aims to provide a ‘‘minimum” level of safety through the prevention of ‘crucial events’, which the Directive refers to as ‘critical events’. A ‘crucial event’ is defined as ‘‘an event which may lead to harm” (Beard, 2005a,b). However, Dix has pointed out that the Directive provides a minimal provision for fire safety but that this may not be enough to discharge the legal responsibility of engineers (Dix, 2004a,b, 2005). Dix also compares some of the requirements of the Directive and compares it with the requirements of Germany and Switzerland to illustrate the minimal nature of the requirements in the Directive. See Table 1. The possible effects on tunnel safety of the insurance companies and large investors is mentioned as well as the possible effects of global warming and malicious acts. Specific tunnel cases are looked at briefly including six European tunnels and five non-European tunnels. The Report also considers briefly some strategic and specific issues. These cover a wide range from the vital question of ‘‘what might constitute a ‘healthy mixture’ of prescriptive requirements, qualitative risk assessment and quantitative risk assessment?” to the need to assess fully the stock of existing railway tunnels in Europe concerning risk. Historically, in general, rail tunnels have a better safety record than road tunnels. This, though, should not cause us to be complacent. In a report commissioned after the Mont Blanc fire of 1999 (OPECST, 2000), it is stated that before the Mont Blanc fire the tunnel had been regarded as relatively safe because in 34 years of operation only 17 fires had been reported, 12 of which had been extinguished by the drivers and five by the operators. In Europe there are a very large number of older tunnels, many over 100 years old. The average age for railway tunnels in Europe is about 70 years. Another specific issue raised, in relation to road tunnels, is that hydrogen-powered vehicles are already going through tunnels and yet there is reason for serious concern. 3.3. Recommendations Twenty five recommendations are made including, for example: the need to assess possible new hazards posed by high speed rail-
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Table 1 Comparison of requirements for mechanical ventilation in tunnels for EU Directive (EU); Germany (D) and Switzerland (CH). For the case of uni-directional congested tunnels of different lengths. Re-drawn from Dix (2004b), Ó A.N.Beard. Tunnel length (m) EU D CH CH
<100
100–500 d
500–600 d
600–800 d d
800–1000
1000–1200
1200–1500
1500–3000
>3000
NB
d d d
d d d d
d d d d
d d d d
d d d d
RA DD LR HR
Key: , not mandatory for all tunnels; d, mandatory for all tunnels. NB: RA, may be varied if risk assessment demonstrates acceptable in special circumstances; DD, detailed decisions about smoke extraction etc. driven by requirements of fire case; LR, lower risk-ventilation decisions driven by risk analysis; and HR, higher risk-ventilation decisions driven by risk analysis.
way lines and the need to ensure that designs for tunnel safety include effective measures for the evacuation of elderly and disabled people and not the ‘average person’ only. It is also specifically recommended that hydrogen-powered vehicles be banned from passing through road tunnels, at least until much more research has been carried out and much more consideration has been given to the problem. This is because there is strong evidence that such vehicles pose a considerable hazard in tunnels. Recommendations also include measures to try to ensure the acceptable use of models in relation to tunnel fire safety design. This includes the establishment of a regulatory framework which would cover models, how they are used and the users. There is a great need for ‘knowledgable users’ and acceptable ‘methodologies of use’ as part of this to try to ensure that models are employed in an acceptable way and not used in an inappropriate way or results mis-interpreted. This links to the educational system. It is also recommended that the source codes of computer-based models which are employed as part of safety decision-making be openly available for examination by the scientific community and the public in general; at a minimal charge, if any. This is because assumptions and conditions are sometimes in the source code but are not readily apparent in the documentation.
4. Conclusion A large number of serious tunnel fires have taken place in Europe in recent years. As a result of this the European Parliament requested the author to conduct a study and make recommendations for consideration in relation to future policy on tunnel safety, in particular with regard to decision-making and risk assessment. The resulting Report (Beard and Cope, 2008) was published in 2008 and is available on the web-site of the European Parliament. It makes 25 recommendations covering a wide range of topics, from general to specific. Inter alia it is concluded that risk assessment techniques may play a very valuable part in tunnel safety decision-making but there are significant problems associated with using theoretical models, especially computer-based models, as part of the process. A regulatory framework is outlined which is intended to help to move towards a system in which models may be used in a generally acceptable way. Overall, the report is intended to help to stimulate moves towards a more rational system of tunnel safety decision-making. Specific recommendations are also made, for example in relation to hydrogen-powered vehicles and evacuation of the disabled and elderly. A central theme in the report is the need to account for the fact that ‘the system
changes’, for example traffic patterns, and constant vigilance is required to try to assess changes and take account of them. Every tunnel has problems unique to itself as well as problems in common with others. It is hoped that this Report will help a move towards a better understanding of how tunnel safety decisionmaking may be improved and made acceptable to all, from the general public who use the tunnels to designers, regulators and emergency services; in Europe and world-wide.
References Beard, A.N., 1992. On comparison between theory and experiment. Fire Safety Journal 19, 307–308. Beard, A.N., 2000. On a priori, blind and open comparisons between theory and experiment. Fire Safety Journal 35, 63–66. Beard, A.N., 2005a. Problems with using models for fire safety. In: Beard, Alan, Carvel, Richard (Eds.), The Handbook of Tunnel Fire Safety. Thomas Telford, London. Beard, A.N., 2005b. Prevention and protection: general concepts. In: Beard, Alan, Carvel, Richard (Eds.), The Handbook of Tunnel Fire Safety. Thomas Telford, London. Beard, A.N., Cope, D., 2008. Assessment of the Safety of Tunnels. Commissioned by the European Parliament; Report IP/A/STOA/FWC/2005-28/SC22/29. Published in February 2008 on the European Parliament web-site under the rubric ‘Science and Technology Options Assessment’ (STOA). Dix, A., 2004a. Risk management takes on a key role. Tunnel Management International 7, 29–32. Dix, A., 2004b. Safety standards for road and rail tunnels – a comparative analysis. In: International Conference on Tunnel Safety & Ventilation. Technical University of Graz, Austria (19–21st April 2004). Dix, A., 2005. Tunnel fire safety and the law. In: Beard, Alan, Carvel, Richard (Eds.), The Handbook of Tunnel Fire Safety. Thomas Telford, London. EU Directive document 2004/54/EC, 2004. Official Journal of the European Union (29th April 2004). EUROTAP, 2006. Organized via the German Automobile Association (ADAC). Available from:. The International Tunnelling Insurance Group, 2006. A Code of Practice for Risk Management of Tunnel Works. Johnson, P., 1991. Letter to the editor. Fire Safety Journal 17, 415–416. Kauer, C., 2001. Safety features and principles of the Gotthard base tunnel. In: 4th International Conference on Safety in Road and Rail Tunnels, Madrid, pp. 385– 394. Norwegian Public Roads Administration, 2006. Vision, Strategy and Targets for Road Traffic Safety in Norway. OPECST, 2000. Rapport sur Securite des Tunnels Routiers et Ferroviaires Francais. Office Parliamentaire d’Evaluation des Choix Scientifiques et Technologiques, Paris (in French). Available from: . Rein, G., Empis, C., Carvel, R. (Eds.), 2007. The Dalmarnock Fire Tests: Experiments and Modelling. The School of Engineering, Edinburgh University. ISBN 978-09557497-0-4. Santos-Reyes, J., Beard, A.N., 2005. A systemic approach to tunnel fire safety management. In: Beard, Alan, Carvel, Richard (Eds.), The Handbook of Tunnel Fire Safety. Thomas Telford, London.
Contents lists available at ScienceDirect
Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust
Technical note
Tunnel safety, risk assessment and decision-making Alan N. Beard * Civil Engineering Section, School of the Built Environment, Heriot-Watt University, Edinburgh, Scotland EH14 4AS, United Kingdom
a r t i c l e
i n f o
Article history: Received 30 July 2008 Received in revised form 15 July 2009 Accepted 15 July 2009 Available online 18 September 2009 Keywords: Tunnel safety Risk assessment Decision-making
a b s t r a c t This article gives a brief account of a project which was commissioned by the European Parliament and which has resulted in a report which has been published and is available on the web-site of the European Parliament [Beard, A.N., Cope, D., 2008. Assessment of the Safety of Tunnels. Commissioned by the European Parliament; Report IP/A/STOA/FWC/2005-28/SC22/29. Published in February 2008 on the European Parliament web-site under the rubric ‘Science and Technology Options Assessment’ (STOA)]. The project was funded by a grant from the European Parliament. The author was requested to carry out a study of tunnel safety and make recommendations to be considered for possible application within the European Union. The background to the project was the large number of catastrophic tunnel fires which have taken place in Europe since 1995. Twenty five recommendations are made within the Report the purpose of which is to help to increase tunnel safety in the European Union and, primarily, to help to move towards a common system of tunnel safety decision-making and risk assessment. This article focuses on some aspects of the content. However, it should not be assumed that aspects which are not included here are of lesser importance. Ó 2009 Published by Elsevier Ltd.
1. Introduction This article gives a very brief account of a ten-month project which resulted from the European Parliament requesting the author to conduct a study on tunnel safety. The focus of the study is on the process of decision-making and risk assessment rather than specific factors affecting tunnel risk, although some specific factors which have emerged have been included in the Report. The intention was to make recommendations for consideration by the European Parliament with a view to possible implementation. The approach taken has been wide-ranging; both road and rail tunnels are included. Categories not included are: (a) tunnels under construction, (b) malicious acts, and (c) underground railway/metro systems. Although these categories were nominally not included mention has been made of them to some extent. Over the last 15 years there has been a great increase in the building of both road and rail tunnels, world-wide. In particular, in some countries the rate of tunnel construction has been rapid. For example, before 1995 Shanghai did not have a metro system. By the end of 2007 it had eight lines with a total length of 227 km and 161 stations, although not all the system is underground. More lines are under construction in Shanghai. Globally, not only are many tunnels being constructed but the length and complexity of tunnel systems is increasing and tunnels are forming parts of complex systems; for example, the Oresund link between Sweden and Den* Tel.: +44 131 451 4414; fax: +44 131 451 4617. E-mail address: [email protected] 0886-7798/$ - see front matter Ó 2009 Published by Elsevier Ltd. doi:10.1016/j.tust.2009.07.006
mark includes a bridge and a tunnel. Also, it has been stated that the Gotthard Base Tunnel, currently being constructed in Switzerland, will, at 57 km, be the longest tunnel in the world (Kauer, 2001). The construction of the Channel Tunnel between France and England stimulated both theoretical and experimental research work. Unfortunately this did not prevent a very serious fire taking place in the Channel Tunnel about 2 years after opening. Luckily there was no loss of life in that fire, although the story may have been very different if the fire had started close to the amenity coach in which the heavy goods vehicle (HGV) drivers had been travelling and not close to the other end of the train, as actually happened. Probably the most serious underground fire to date took place in the Baku underground railway metro system in Azerbaijan on 28th October 1995. In that fire approximately 300 people lost their lives. Since then there have been several other serious fires in tunnels, including the fires at Mont Blanc, Tauern, St Gotthard and Kaprun, right up to the Viamala Tunnel fire, Switzerland (2006), which killed nine people. Also, there is the Burnley Road Tunnel fire, Melbourne (2007), in which three people died from the initial crash and the Santa Clarita Road Tunnel fire in California (2007) in which three died. Overall, there has been a significant increase in serious tunnel fires over the last 15 years, resulting in many fatalities. This is probably related to the considerable increase in traffic over these years and especially the great increase in HGV traffic passing through tunnels. Simultaneously, over the last 15 years, there has been an increase in the use of risk assessment techniques although there
92
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has been no uniformity as to what this should involve. Also, an initiative aimed at furthering the use of risk assessment techniques in tunnel construction has come from major insurance companies such as Swiss Re and Allianz AG and a document has been prepared under the aegis of The International Tunnelling Insurance Group (International Tunnelling Insurance Group, 2006), which is expected to have a major impact on tunnel projects (Dix, 2004a). It may have an effect on design and operation as well. If the Code is not met during construction then insurers may withdraw cover and without insurance projects would not be able to continue. In this overall context the European Parliament commissioned a study aimed at improving tunnel safety and assisting in moving towards an acceptable, common, system of decision-making and risk assessment in the European Union. The final Report has been placed on the European Parliament’s web-site under the aegis of the ‘Science & Technology Options Assessment’, i.e. (STOA) initiative.
Fig. 1. Road tunnels: numbers of fatalities in fires world-wide (1987–2006), by vehicle involvement. Total = 96 (Not inc. during construction or malicious.) Ó A.N.Beard.
involving HGVs, see Fig. 1. It would be desirable to reverse the trend for more and more freight to be transported by road rather than rail; in Western Europe the rail share is around 8%, down from about 21% in 1970.
2. The areas covered The main topics included in the Report are: (a) Setting the scene: an overall description of the present position; (b) Tunnel design and risk assessment: this is the largest section considering prescriptive requirements and risk assessment, modelling, qualitative and quantitative aspects, criteria for acceptability of risk and safety management. This section also considers the need for an extensive and continually up-dated knowledge base; (c) Regulatory initiatives, including the EU Directive of 2004 (EU Directive document 2004/54/EC, 2004); (d) Other influences on tunnel safety, e.g. global warming; (e) Particular tunnel cases: a brief account of some specific tunnel projects; (f) Strategic and specific issues; (g) Recommendations, of which there are 25.
3. Key points from the Report The Report considers both road and rail tunnels, with an emphasis on road tunnels. It is pointed out that, although historically the risk has been less in rail tunnels than in road tunnels, the rail tunnel stock in Europe is very old and many have very poor fire-fighting and escape features. In 1998 the risk, historically, may have been regarded as relatively low in road tunnels but since that date we have seen many disastrous road tunnel fires. It is necessary to look at the system itself and to consider changes to systems, such as traffic volumes and vehicle types, rather than be mesmerized by historical statistics. Systems change and it is essential to be aware of that and try to take account of it. In the following a few points only are mentioned, to give a flavour of the content of the Report. This does not mean that topics which are not mentioned are of lesser importance. For more details and references, see Beard and Cope (2008). 3.1. Setting the scene It appears to be the case that, overall, most deaths in tunnel incidents result from common traffic accidents (about two-thirds) and it is essential to address this as well as fire-related incidents which are more likely to result in multiple fatalities. Fatalities in road tunnel fires are strongly associated with heavy goods vehicles (HGVs); approximately 71% of fatalities in tunnel fires are in fires
3.2. Tunnel design and risk assessment Quantitative risk assessment is coming to be used as part of tunnel safety decision-making and this may or may not be a desirable development depending upon how it is carried out. The use of quantitative risk assessment has the potential for leading to unacceptable designs. It is necessary to adopt a broad perspective and be aware of the possible pitfalls of risk assessment. Risk assessment is not a panacea; it is a tool and, like all tools, it may be inappropriate for a task or used badly. Overall, a new tunnel may be designed, or an existing tunnel up-graded, through the use of prescriptive regulations, qualitative risk assessment or quantitative risk assessment; or a mixture of these. Beyond that, quantitative risk assessment may then be composed of deterministic risk assessment (i.e. using deterministic models, e.g. computational fluid dynamics models or zone models) or non-deterministic risk assessment (e.g. using models such as fault trees, stochastic models or points schemes such as EUROTAP (EUROTAP, 2006)); or a mixture of the two. Results from physical models may also be used, for example in the form of small-scale or large-scale tests. Many more large-scale tests are necessary in addition to small-scale (Johnson, 1991; Beard, 1992); and on a continual basis because ‘the system’ is continually changing. Carrying out large-scale tests is expensive, but vital in order to inform the knowledge base which under-pins decision-making in general and risk assessment in particular. When shifting to an approach which includes risk assessment the following questions arise: (a) which methodology should be used in order to conduct a risk assessment? What are to be the criteria for acceptability of a methodology? (b) Which models should be employed, and how, to assess the risk and make a decision? What are to be the criteria for acceptability of a model and how it is used? (c) What are to be the criteria for acceptability of risk?; this is basically an ethical decision, not a technical one, as such the criteria need to be generally acceptable to the public. Further, to support the above a comprehensive knowledge and understanding of the system is needed; i.e. a ‘knowledge base’ needs to be in existence and continually up-dated. This means there is a need for both theoretical and experimental research and gathering of information/data; this needs to be on a continual basis because the real world system, and its values, changes all the time. The Report argues for the establishment of a ‘One Stop Shop’ for the European Union which would act as a centre for the comprehensive gathering of information, e.g. statistical data on tunnel safety, as well as information about what research has been done
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and what is under-way. Such a ‘Shop’ would serve as a very valuable resource for all those conducting tunnel safety risk assessments, as well as being available to other interested parties, e.g. operators, emergency services, regulators and other concerned people. The Report goes on to consider problems with using theoretical models as part of fire safety decision-making. It is often stated in the literature that a model has been ‘validated’ and the implication is that the model has been ‘proven correct’. It is, however, impossible to prove a model to be ‘correct’. An example of the kinds of problems involved is illustrated in a recent ‘round-robin’ exercise (Rein et al., 2007) in which eight groups used the same computational dynamics (CFD) model to predict the values of variables such as temperature expected in an experimental test. The comparisons were carried out on an a priori basis; i.e. the users had effectively not ‘seen’ or used any of the results from the experiment (Beard, 2000). As a general rule, the predictions were not at all good. There was generally a wide scatter amongst the predictions by users and, also, predictions usually compared poorly with experimental results. Although this study relates to a non-tunnel case the general conclusions would certainly be expected to pertain to tunnels as well. It is pointed out that the testing of models is problematic and has been discussed in Beard (2005a,b). In principle, results from deterministic models can be compared with experiment; however, how the comparison is carried out is very important (Beard, 2005a,b). Also, it must be realized that experimental data are not necessarily ‘hard and fast’ but are subject to, for example, uncontrolled variables. Even experiments which are intended to replicate earlier experiments and should, in principle, produce identical results may not do so and the differences between results from ‘identical’ experiments may be considerable, see Beard (2005a,b). Comparison between theory and experiment is not a straight forward process and different kinds of comparisons need to be carried out (Beard, 2005a,b). Probabilistic models cannot be directly compared with experiment and testing is more problematic. The only real test for a probabilistic model of a system is to compare with historical statistical data for the system of concern. In that case it would be extremely important to ensure that the model’s results and the historical data were at the same abstraction level; see Beard (2005a,b). Not comparing at the same abstraction level, i.e. ‘like with like’, is one of the sins of statistical analysis and one way of ‘lying with statistics’ (Beard, 2005a,b). A regulatory framework needs to be created so that models, especially computer-based models, may become generally acceptable as part of safety decision-making. In general, what is required is: [1] A model which has the potential to be valuable for decisionmaking in a specific case; in general more than one model may be used in a given case. [2] A ‘Methodology of Use’, which is generally acceptable and encourages a user to be comprehensive and explicit. [3] A ‘Knowledgeable User’, who is capable of employing an acceptable ‘methodology of use’ in a comprehensive and explicit manner to a model which has the potential to be valuable in a specific case, and of interpreting results justifiably. Concerning criteria for acceptance of risk, the Report points out that, internationally, different criteria have been used and there is a need for coherence. It is mentioned that the Norwegian Government has adopted a ‘Vision Zero’ policy which aims to reduce road deaths steadily year by year (Norwegian Public Roads Administra-
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tion, 2006). Sweden and Denmark also have ‘Vision Zero’ policies. Reducing road traffic accidents in general would include road traffic accidents in tunnels. Whilst reducing the probability of fatalities to zero is not realistic, as a guiding vision it may be regarded as extremely valuable, as long as it is genuinely acted upon year by year. Whether or not such a policy should be adopted across the European Union needs to be decided. If such a policy were to be accepted it would need to be ensured that real changes were taking place, year by year, ‘on the ground’ and that the policy did not exist largely on paper only. The fact that ‘the system changes’ would need to be taken into account. For example, there has been a considerable change in traffic patterns related to tunnels over the last 40 years with far more HGVs amongst other changes. Gradual changes in the system like this need to be consciously looked for and not allowed to ‘creep up’ on us. A research effort aimed at gauging current and future changes needs to take place. This would have an input to the ‘One Stop Shop’ mentioned above. Safety management is considered briefly in the Report and the need for such systems to be as ‘systemic’ as possible (Santos-Reyes and Beard, 2005). Also considered is the great need for a knowledge base which would be continually up-dated and supported by both theoretical and experimental research. Some of the tunnel research projects which have been conducted over the last few years, largely funded by the European Union, are described very briefly. Concerning regulation, the EU Directive of 2004 on minimum requirements for tunnels in the Trans-European Road Network is discussed to some extent. The Directive aims to provide a ‘‘minimum” level of safety through the prevention of ‘crucial events’, which the Directive refers to as ‘critical events’. A ‘crucial event’ is defined as ‘‘an event which may lead to harm” (Beard, 2005a,b). However, Dix has pointed out that the Directive provides a minimal provision for fire safety but that this may not be enough to discharge the legal responsibility of engineers (Dix, 2004a,b, 2005). Dix also compares some of the requirements of the Directive and compares it with the requirements of Germany and Switzerland to illustrate the minimal nature of the requirements in the Directive. See Table 1. The possible effects on tunnel safety of the insurance companies and large investors is mentioned as well as the possible effects of global warming and malicious acts. Specific tunnel cases are looked at briefly including six European tunnels and five non-European tunnels. The Report also considers briefly some strategic and specific issues. These cover a wide range from the vital question of ‘‘what might constitute a ‘healthy mixture’ of prescriptive requirements, qualitative risk assessment and quantitative risk assessment?” to the need to assess fully the stock of existing railway tunnels in Europe concerning risk. Historically, in general, rail tunnels have a better safety record than road tunnels. This, though, should not cause us to be complacent. In a report commissioned after the Mont Blanc fire of 1999 (OPECST, 2000), it is stated that before the Mont Blanc fire the tunnel had been regarded as relatively safe because in 34 years of operation only 17 fires had been reported, 12 of which had been extinguished by the drivers and five by the operators. In Europe there are a very large number of older tunnels, many over 100 years old. The average age for railway tunnels in Europe is about 70 years. Another specific issue raised, in relation to road tunnels, is that hydrogen-powered vehicles are already going through tunnels and yet there is reason for serious concern. 3.3. Recommendations Twenty five recommendations are made including, for example: the need to assess possible new hazards posed by high speed rail-
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Table 1 Comparison of requirements for mechanical ventilation in tunnels for EU Directive (EU); Germany (D) and Switzerland (CH). For the case of uni-directional congested tunnels of different lengths. Re-drawn from Dix (2004b), Ó A.N.Beard. Tunnel length (m) EU D CH CH
<100
100–500 d
500–600 d
600–800 d d
800–1000
1000–1200
1200–1500
1500–3000
>3000
NB
d d d
d d d d
d d d d
d d d d
d d d d
RA DD LR HR
Key: , not mandatory for all tunnels; d, mandatory for all tunnels. NB: RA, may be varied if risk assessment demonstrates acceptable in special circumstances; DD, detailed decisions about smoke extraction etc. driven by requirements of fire case; LR, lower risk-ventilation decisions driven by risk analysis; and HR, higher risk-ventilation decisions driven by risk analysis.
way lines and the need to ensure that designs for tunnel safety include effective measures for the evacuation of elderly and disabled people and not the ‘average person’ only. It is also specifically recommended that hydrogen-powered vehicles be banned from passing through road tunnels, at least until much more research has been carried out and much more consideration has been given to the problem. This is because there is strong evidence that such vehicles pose a considerable hazard in tunnels. Recommendations also include measures to try to ensure the acceptable use of models in relation to tunnel fire safety design. This includes the establishment of a regulatory framework which would cover models, how they are used and the users. There is a great need for ‘knowledgable users’ and acceptable ‘methodologies of use’ as part of this to try to ensure that models are employed in an acceptable way and not used in an inappropriate way or results mis-interpreted. This links to the educational system. It is also recommended that the source codes of computer-based models which are employed as part of safety decision-making be openly available for examination by the scientific community and the public in general; at a minimal charge, if any. This is because assumptions and conditions are sometimes in the source code but are not readily apparent in the documentation.
4. Conclusion A large number of serious tunnel fires have taken place in Europe in recent years. As a result of this the European Parliament requested the author to conduct a study and make recommendations for consideration in relation to future policy on tunnel safety, in particular with regard to decision-making and risk assessment. The resulting Report (Beard and Cope, 2008) was published in 2008 and is available on the web-site of the European Parliament. It makes 25 recommendations covering a wide range of topics, from general to specific. Inter alia it is concluded that risk assessment techniques may play a very valuable part in tunnel safety decision-making but there are significant problems associated with using theoretical models, especially computer-based models, as part of the process. A regulatory framework is outlined which is intended to help to move towards a system in which models may be used in a generally acceptable way. Overall, the report is intended to help to stimulate moves towards a more rational system of tunnel safety decision-making. Specific recommendations are also made, for example in relation to hydrogen-powered vehicles and evacuation of the disabled and elderly. A central theme in the report is the need to account for the fact that ‘the system
changes’, for example traffic patterns, and constant vigilance is required to try to assess changes and take account of them. Every tunnel has problems unique to itself as well as problems in common with others. It is hoped that this Report will help a move towards a better understanding of how tunnel safety decisionmaking may be improved and made acceptable to all, from the general public who use the tunnels to designers, regulators and emergency services; in Europe and world-wide.
References Beard, A.N., 1992. On comparison between theory and experiment. Fire Safety Journal 19, 307–308. Beard, A.N., 2000. On a priori, blind and open comparisons between theory and experiment. Fire Safety Journal 35, 63–66. Beard, A.N., 2005a. Problems with using models for fire safety. In: Beard, Alan, Carvel, Richard (Eds.), The Handbook of Tunnel Fire Safety. Thomas Telford, London. Beard, A.N., 2005b. Prevention and protection: general concepts. In: Beard, Alan, Carvel, Richard (Eds.), The Handbook of Tunnel Fire Safety. Thomas Telford, London. Beard, A.N., Cope, D., 2008. Assessment of the Safety of Tunnels. Commissioned by the European Parliament; Report IP/A/STOA/FWC/2005-28/SC22/29. Published in February 2008 on the European Parliament web-site under the rubric ‘Science and Technology Options Assessment’ (STOA). Dix, A., 2004a. Risk management takes on a key role. Tunnel Management International 7, 29–32. Dix, A., 2004b. Safety standards for road and rail tunnels – a comparative analysis. In: International Conference on Tunnel Safety & Ventilation. Technical University of Graz, Austria (19–21st April 2004). Dix, A., 2005. Tunnel fire safety and the law. In: Beard, Alan, Carvel, Richard (Eds.), The Handbook of Tunnel Fire Safety. Thomas Telford, London. EU Directive document 2004/54/EC, 2004. Official Journal of the European Union (29th April 2004). EUROTAP, 2006. Organized via the German Automobile Association (ADAC). Available from: