Clear and present danger: stopping suicide bombers

The suicide bomber is an ideal tool for a terrorist. The bomber is able to choose the precise moment at which to detonate their device and does not require an escape plan, making countering such a threat significantly more difficult than that presented by other forms of terrorism. As such, British police officially refer to suicide bombers as 'deadly and determined attackers'.

The tactic of suicide bombing has been employed for hundreds of years. The Jewish Sicaris conceived suicide attacks as a legitimate tactic in the 1st century AD, while the Islamic Hashishiyun (assassins) used suicide attacks to further their political aspirations in the 11th century. By the 18th century, suicide tactics were commonplace and occurring in India, Sumatra and the Philippines as part of campaigns to defeat colonial rule. But while historically the inhabitants of the Middle East and Asia were predominantly the victims of its effects, the nature of suicide bombing has significantly changed in recent years.

Today we are faced with two types of suicide bomber, 'the rational' and the 'irrational'. The Sri Lankan Liberation Tigers of Tamil Eelam (LTTE) provide a good example of the rational suicide bomber. The LTTE have a definite political goal and has focused its attacks on military and government targets in order to achieve this. In contrast, irrational suicide bombers, such as groups affiliated to al-Qaeda, belong to organisations with less clearly stated aims and are willing to attack 'soft' and indiscriminate targets in order to instil terror.

Tactics and threat facing the UK

Different groups of suicide bombers employ different tactics, including differences in the weight of the device and method of its delivery. The greatest threat presented from suicide bombing is vehicle-borne suicide attacks, due to the weight of the devices that can be used. A non-vehicle delivered suicide explosive device is generally between 5 kg and 10 kg, as any heavier device becomes difficult to conceal. While the maximum weight of a vehicle-delivered suicide device can exceed 200 kg, it is unlikely to weigh more than 500 kg as heavier devices need multiple detonators. This is because most groups have difficulty in successfully detonating a single detonator due to poor quality of home made detonators, so increasing the number of detonators will reduce the chance of a successful attack.

The main threats against UK targets presented by suicide bombers originate in groups affiliated to or inspired by al-Qaeda. One such group of people demonstrated their intent and capabilities with the detonation of four devices in London on 7 July 2005. The men involved were able to produce at least four devices, which were contained in backpacks. These devices were detonated on three London Underground trains and a London bus, killing 56 people, including the four bombers. After the attacks, a significant amount of explosive material belonging to the group was also discovered. Although the British security services had been aware of the possibility of such an attack for a number of years, the bombings still had a shocking effect on the government.

Perhaps most surprising is that all four bombers were UK citizens who had grown up in the country and appeared to live integrated and happy lives. The bomber who detonated his device on the bus almost an hour after the other three explosions had occurred had repeatedly attempted to phone one of the other bombers after the first three explosions. It is unclear whether the bomber was confused about his role, or if he had decided he did not want to go through with his part of the attack.

Despite the popular image presented by groups in Gaza and the West Bank and Iraq of suicide terrorists as welcoming death, fear among suicide bombers is not unusual and there are many instances of bombers refusing to execute an attack. The Chechen group the Black Widows has developed a way of preventing this from happening. The group recruits women who have lost loved ones in the fight against Russia and trains them as suicide bombers. The group will then give a woman a target and an explosive device, before following her to the agreed location. If the woman fails to detonate her device, the person following her will then remotely detonate the explosives. This reduces the number of failures and the chance of anyone being arrested and questioned.

Palestinian terrorist groups have not yet employed this tactic and there is nothing to indicate they have any plans to do so in the near future. These organisations rely on the their suicide operatives' dedication to the cause. Groups in Palestine operate quite openly and only keep the identities of potential new suicide bombers and their training areas a secret in order to prevent them being targeted by the Israeli Defence Force.

While it is always difficult to predict who will become a suicide bomber and stop them reaching their target, there is an ever-improving understanding of how to protect buildings from suicide bombers.

One of the greatest uncertainties in considering the appropriate practical and cost-effective blast hazard mitigation solutions against a bomb attack is the charge weight (usually expressed as TNT equivalent) and stand-off distance (the distance between the centre of the explosive device and, for example, the facade of a building). Generally, buildings designed in accordance with the UK building regulations and British standard codes of practice should ensure that damage is in proportion to its cause.

Suicide vehicle attacks

Although not yet seen in the UK, global events show that a suicide attack using a vehicle as a battering ram to deliver a bomb close to or inside a building is a credible threat. In such an attack, detonation is usually immediate once the vehicle has reached its target. To reduce the risk of a rammed vehicle attack, consideration could be given to installing vehicle barriers on the footpaths around a building.

The benefits of this are probably as much psychological as physical and act both as a possible deterrent to potential attackers while also providing reassurance to people in the building. However, deterrent security measures such as planters have limited benefit against committed and determined attackers. Most of the hazards to occupants come firstly from the facade of the building and then from collapsing parts of the structure. Providing a suitable building facade with appropriate blast hazard mitigation should be considered.

Hand delivered suicide bombs

The 7 July incidents on the London transport network show the potential for simultaneous organised and meticulously implemented suicide hand delivered improvised explosive devices in the UK. In such an attack, detonation is usually immediate once the attacker or attackers have reached their target. In this case, the consequences for people in the immediate vicinity may be catastrophic and emergency procedures for a bomb alert would be irrelevant.

However, structural damage would be locally confined to the base of the explosion. While devastating to people on the floor where the bomb detonates and possibly to people on the floor immediately below, structural damage is unlikely to extend to the floor above or below.

If a hand delivered suicide bomb is detonated close to a single column it is possible that it may be damaged but other columns on the same floor plate would be unlikely to suffer more than minor impact damage from fragments. There could be minor slab damage above or below the device but the floor slab would not be expected to collapse.

Those people directly adjacent to the exploding device are likely to be killed while others in the vicinity are likely to suffer varying degrees of injuries, ranging from life threatening to minor. The explosion effects from a hand delivered improvised explosive device would be localised, and the blast pressure and impulse would diminish rapidly with distance. The primary source of injury to occupants may arise from high velocity fragments from the bomb.

It is nearly impossible to prevent suicide bombers in uncontrolled public spaces, but measures can be implemented to make perpetrating such an attack difficult. These include, but are not limited to, CCTV surveillance, overt presence of identifiable security personnel and the implementation of random stop and search procedures.

Mitigation against the consequences of suicide bombers by providing a screening room located within an existing building foyer may be prudent. Implementation of such an option would provide a visual deterrent against an ad-hoc attacker but not a deadly and determined attacker such as a suicide bomber. With suitable equipment, the screening should detect the bomber and appropriate action can then be taken. The primary objective of the screening room would be diminishing the blast pressure in the surrounding area and absorbing high velocity fragments. Screening rooms may be transparent (the provision of purpose engineered laminated glass) or opaque (the provision of profiled metal sheeting).

Future considerations

Before becoming unduly alarmist about suicide bomb attacks, it is worth remembering that the vehicle-based bomb is likely to remain the most favoured weapon in a terrorist's arsenal. The modus operandi of the terrorist in delivering a vehicle bomb, whether static or rammed, will depend on a number of factors. At the early stages of a construction project it is worth considering the landscaping layout and access provisions onto and away from the site. Consideration should also be given to suitable barriers at the kerbside to deter or deflect away a rammed vehicle attack and to prevent a vehicle from parking immediately next to a load-carrying part of a structure.

It was clear from the Provisional IRA bombings in the City of London in 1993 and the London Docklands bombing in 1996 that the most hazards to people came from the glazed facade of buildings being breached. Therefore, consideration should be given to the design and implementation of a suitable building envelope that would mitigate glazing blast hazards to occupants. Integration of personnel and baggage screening rooms should be also considered in the early stages of a building design in order to limit the likelihood of a suicide bomber entering a building and killing or injuring the people inside.

Kate Wheadon is a threat consultant for Arup Security Consulting. She previously worked for the Cranfield Mine Action and Disaster Management Centre at Cranfield University, Royal Military College of Science, where she specialised in counterterrorism in Southeast Asia. Ryan Sukhram, who also works for Arup Security Consulting, provides advice on the effect of explosives and blast hazard mitigation solutions of buildings, the design of structures against blast loading, structural robustness and resilience to threats from various weapons.

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