Fighting terror by design
Last week's Madrid bombings exposed the vulnerability of train stations. But there are measures that can be taken at the design stage. James Dennison explains
The appalling bomb attacks on commuter trains in Madrid last week have thrown the issue of railway security into sharp relief. Of course, maintaining security against the threat of terrorism will always primarily be a job for the police and the intelligence services. But building design can have a vital role in controlling access and, when the worst does happen, in mitigating the effects of terrorist strikes on rail buildings and their users.
'Railway stations are, by definition, a security nightmare, ' admits Mark Whitby, director at structural engineer Whitbybird. 'Big, open spaces, packed with unscreened strangers carrying unchecked baggage, they require unrestricted access and are invariably in the middle of densely built-up areas.
So traditional perimeter measures like bollards and vehicle exclusion zones are useless.'
But just because this vulnerability is built-in doesn't mean that some of it can't also be designed out. 'Anyone who has worked on a rail project will know that the fisafety-firstfl culture is absolutely paramount, ' says Grimshaw's Mark Middleton, working on the extension of London's Paddington Station.
'It infuses everything from signalling and track maintenance to crowd control and emergency planning. Stations are already designed with a finightmare scenariofl in mind, like a burning, runaway train derailing as it enters the station and taking out some of the structure. Set procedures are in place to cope with such an event, covering everything from the PA system to refuge zones and escape routes, with redundancy built-in throughout.'
Indeed, thanks to decades of bitter experience at the hands of the IRA, the UK leads the way in counter-terrorist design. 'Perhaps the biggest challenge is the change in terrorist type, ' says Arup security director John Haddon. 'In this country, almost all terrorism had been by Irish republicans, who give warnings and go for economic targets rather than killing people.
The new threat is suicide bombers whose sole aim is to take lives, including their own.'
Haddon believes taking suicide bombers into account means stepping up existing security measures rather than fundamentally rethinking design guidance. 'The measures developed over the past decades are still valid, ' he says. 'First and foremost, you have to minimise the likelihood of occurrence. It's not about fortifying buildings - there are too many scenarios; you'd just end up with a bunker.'
In railway stations where access can't be controlled (the best defence against bombers), this means designing out places of concealment, improving the lighting and reducing clutter to give CCTV cameras a clear field of vision. This extends to details like ensuring window sills, vending machines and phone booths are angled to prevent packages being left on them. Bins should consist of nothing more than rubber hoops with clear plastic bags hung from them.
'They're simple measures but they work, ' says Geoff Dunmore, operational security manager at London Underground. 'In August 1994 our cameras caught the IRA trying to plant a bomb in Oxford Circus Tube Station.
They couldn't find anywhere to place it so ended up dumping it in a bin outside.'
In the future, sensitive airport-style 'sniffer' booths could be installed, which pick up minute traces of explosive chemicals on people entering stations, but are expensive and can aggravate problems of congestion. Traditional paper tickets could be phased out in favour of 'smart' credit-card-style tickets, which identify and track passengers as they pass through the system. Oyster cards, like this, are already in use on the London Underground and could help to identify suspect passengers in the event of an attack. Both, however, raise civil liberties issues.
If the worst does happen, glazing is the most critical area of safety, as over 95 per cent of blast injuries are caused by flying glass. 'Anti-shatter film is very effective and should be fitted to all existing glazing that isn't laminated - though the frames must also be checked to ensure they can withstand the increased blast loads, ' says David Hadden, Arup Security's facade specialist. 'The ideal is to fit windows with laminated toughened glass at least 6.8mm thick, fully anchored to reinforced frames in rebates at least 25mm deep.' Large panes of glazing (such as station roofs) should have cables stretched beneath them for the glass to wrap around should it be blown from its frame.
The aim behind the structure of stations is the same as for other buildings: to delay collapse long enough for people to escape. Robustness and ductility are the key attributes. 'Buildings with frames of steel or in-situ reinforced concrete exhibit the best resilience to blast loads, ' says Hadden. Precast concrete frames should be avoided unless consideration is given to the blast performance of their connections. Load-bearing masonry buildings also perform badly in blasts.
For security reasons, much blast-mitigation expertise is deliberately withheld from the public domain. But if you are working on a particularly high-risk building, the advice is to contact the police at the design stage and they will put you in contact with the relevant experts on a need-to-know basis.