The public and political focus on possible terrorist attacks on our underground infrastructure has forcefully directed minds (and more often budgets) into dealing with the severe risks posed to both man and structure. Whether these attacks use weapons of mass destruction (biological [e.g. Tokyo, Japan sarin gas 1995], chemical or radioactive), or more traditional explosives [e.g. Paris subway 1995, Moscow subway 2004], involve sabotage or some variation of these techniques, the prophets of destruction within our societies are quick to identify the peculiarities and vulnerabilities of subterranean infrastructure.

The challenge for tunnelling professionals is to meet emotionally charged fear with considered reasoning, which appropriately prioritises factual (as opposed to emotional) risks and ensures that our limited resources are appropriately focused and invested in measures which deliver the highest level of safety and security.

Our disciplines utilise highly developed tools to assist in the delivery of safe and secure facilities. The perceived risks from acts of terrorism are but one class of risks which we routinely deal with and successfully manage.

Because risks of terrorist acts are at worst high consequence low frequency events, they must be placed within an overall risk framework for underground infrastructure. The confounding factor is that such attacks are designed to undermine society’s sense of well-being and to replace it with a sense of vulnerability and unease. It is this sense of vulnerability that challenges our sound methodologies for management of these risks.

Terrorist risk demands systematic analysis using a refinement of the techniques currently used for underground design, operation, refurbishment, incident response and incident recovery. From an engineering perspective the term ‘terrorist’ has only a limited place. It is a measure of the likelihood and type of event to which a structure may be subjected – not a description of a new class of challenges.

The problem psychologically for the engineer is that a terrorist attack is an intentional act designed by another person (perhaps also an engineer) to destroy structures, cause injury and kill people in a civilian context. From an engineering perspective, the only difference between terrorist ‘arson’ attack and a ‘fire’ should be the effect the engineering has had on the probability of the attack – not the fire itself.

Accordingly, all structures have inherent resistance to attack – underground structures in particular having highly complex systems specifically designed to deal with problems caused by factors such as fire, gas, smoke and explosion.

Currently the most serious risk to the logical management of underground infrastructure risk arises from the recently credentialised wave of terrorist advisors who bring concepts of warfare to the prioritisation of limited civilian resources, where in fact the greatest risks to safety usually arise from the routine operational environment.

The inappropriate introduction of military style detection technologies, labour intensive environmental monitoring systems and other capital and human resource intensive technologies, bring new – and often overlooked – risks to the normal operating environment.

It is essential that the agencies within our jurisdictions who are responsible for, or who have had access to, information (intelligence) on the nature of terrorism risk provide that information to those charged with subterranean infrastructure risk management and that the risk be dealt with rationally.

Vulnerability analysis

In order to assess what measures (if any) should be taken with respect to the special risks posed by terrorism, a vulnerability analysis should be undertaken. This is no more than a risk analysis process, which recognises factors that contribute to the risk of a deliberate attack, such as the political context of utility or opportunity.

The political context is merely a measure of the general likelihood that a terrorist act may be performed in that time and location. The opportunity is a systematic analysis of the ease by which such a challenge could be undertaken. Both of these criteria relate to the probability of the selection of the infrastructure. From this point on in the analysis the systematic consideration of the risk can appropriately be dealt with and managed using existing techniques.

The consequences of a terrorist act may then form part of its design analysis for the project – infrastructure is critical whether the event is a premeditated terrorist attack or a non intentional catastrophe.

If, for example, a piece of infrastructure is absolutely critical to the operation of a city it should be designed and managed with that criticality in mind – independently of the emergence of a terrorist risk.

Structural issues

All tunnels have blast, fire, chemical, biological and radiological resistance characteristics. Quantification of their actual performance may be required if the vulnerability analysis indicates that they are, or could reasonably be required to resist such a challenge. This may be important during a structural design (or redesign) phase when computing factors such as: explosion resistance; heat resistance; cross sectional area (and shape); escape routes; and sanctuaries.

Quantifying the performance of a particular design with respect to these parameters (or such of them as is considered appropriate) then allows a considered ‘gap’ analysis of the difference between the performance of the system and that which may be required.

During this portion of a project consideration of intentional challenges can be readily incorporated into the systematic design process. The process should not be ‘hijacked’ by such consideration, as the traditional operational safety issues usually remain the most critical – indeed these features are most likely to be of use in the event of an intentional act of terrorism.

It is to be expected that in many circumstances a thorough examination of the design, and refinement where necessary – will not result in fundamentally different designs being warranted. What is essential is that the basis for such conclusions be documented and confirmation be sought from clients, so that they accept the foundations of such an analysis in order to discharge the designers obligations with respect to this sensitive issue.

System operational issues – configuration

The performance of systems in degraded conditions is a normal part of the design operation and refurbishment process. Whether the need for redundancy is because of a fire in a tunnel or a fire in a tunnel caused by an act of terrorism makes no difference to the systems performance, other than if the likely terrorist act is fundamentally different to a reasonably contemplated degraded conditions scenarios.

For example, in a country which designs its underground infrastructure for the transport of dangerous goods – such as hydrocarbons and explosives – it is likely that the systems’ performance will either be designed to manage such an event or there will have already been a decision that the cost to do so cannot be justified.

On the other hand, where the particular infrastructure is designed specifically not to accommodate large hydrocarbon fires or explosions it may still be considered inappropriate to harden the infrastructure and develop systems to deal with a terrorist challenge.

However, when the operational requirements of a range of deliberate attacks are considered there will be measures which are both effective and efficient which can be undertaken to manage risks. For example, configuration of a ventilation system that allows rapid ventilation transition to zero air movement may be useful in a range of scenarios.

Appropriate system designs using existing design tools can and do deliver well designed, responsive underground system management which provides appropriate levels of safety in an emergency. Just as is the case with conventional emergencies there are legitimately scenarios which although they can be contemplated do not warrant an engineering response.

In a world with limited resources it is both appropriate and necessary to determine what measures are appropriate and accept the inevitability that there will be residual – and acceptable – risks in all human endeavours, including that conducted underground.

The issue which must then be dealt with is the appropriate management of an emergency once a terrorist attack is thought to have occurred.

Management issues

The catastrophes at Mont Blanc, Gotthard and Tauern highlighted the importance of effective communications between relevant emergency services agencies during and following a catastrophe. The confounding problem where a terrorist attack is thought to have caused an incident is that, in most jurisdictions, a range of national and international security agencies will seek to be informed, involved or in some instances even take charge of the emergency.

These agencies are inevitably enthusiastic, well meaning, but in all likelihood naive at best as to the complex operational environment of a particular piece of underground infrastructure in an emergency. It is essential that all tunnel operators establish (as well as practicable) an understanding of whom these agencies might be, the powers that they do (and don’t) have and to amend their emergency procedures accordingly.

Wherever possible, working relationships should be forged with these agencies – such as during emergency exercises, in exactly the same way as such relationships are currently developed with traditional emergency services.

It should be borne in mind that not only is the relationship between the tunnel operator and these agencies important, but that perhaps even to a greater degree, the relationship between police and fire brigade and other civilian agencies, and these anti-terrorist agencies should be fostered due to the risk that in an emergency a serious dispute with respect to issues such as key decisions or even the command of the incident scene could be placed in dispute. This could seriously compromise safety.

The tunnelling industry has over the last 10 years embraced this issue with respect to civilian emergency services agencies – all that is required is an expansion of this to include these ‘other’ agencies.


It is vitally important that the risks posed to underground infrastructure by terrorism be identified and systematically prioritised with all other risks. This necessarily involves a vulnerability analysis of the infrastructure. It is only where such an analysis demonstrates that the structure warrants treatments for terrorist types of risk that the analysis need progress further – with the possible exception of comparatively simple measures.

From an operational perspective, the importance of establishing which agencies may become involved during a terrorist emergency is essential. The existence of national and international secret and semi-secret agencies with a mandate to manage terrorist incidents poses a real and immediate threat to the proper management of the emergency systems designed to protect civilians and infrastructure.

The development of relationships with such agencies will reduce conflicts between attending agencies and the tunnel operator following such an event.

It is the inappropriate prioritisation of resources away from primary safety systems designed for the normal modes of operation, and the potential for conflict in an emergency which must be guarded against.

Our challenge is to meet actual safety threats and rationally prioritise them using our well refined techniques and not let the discussion be driven by those driven by emotions, fear and uncertainty.