Going underground

Published:  19 January, 2012

Industrial Fire Journal's Editor reports on a one-day seminar on the benefits of a systematic approach to fire safety on underground railways, as organised by London Underground, October 2011.

Principal Engineer (Fire Safety) for London Underground (LU) Martin Weller kicked off the one-day seminar with some history on the world’s first underground railway. London Underground (LU) started life in 1863 and will be celebrating its 150th year anniversary in 2013. LU caters for 1bn passenger journeys per year – the same number of journeys as the rest of the mainland UK’s rail put together – along 402km of track and on 511 trains. LU operates 260 stations, 181 of which are subsurface, and employs over 18,500 staff.

In terms of LU’s approach to safety, LU appoints Principal Engineers for each engineering discipline – including Fire, who are each personally accountable for safety, and each hold a suite of engineering safety standards. A separate safety directorate also operates alongside these.

Martin highlighted the fire safety challenges posed by a vast spectrum of infrastructure that includes sections dug by hand by the father of world-renowned engineer Isambard Brunel.

Two major fires were outlined which had significant impact on the LU. The Oxford Circus fire of November 1984 resulted in 14 people hospitalised, and was probably caused by smoking materials pushed into a ventilation grill. This led to a complete ban on smoking in all subsurface LU stations in 1985. It should be noted that smoking had already been banned on LU trains in July 1984.

The King’s Cross fire of 1987 was probably caused by a discarded smoking material igniting rubbish and grease under a wooden escalator. This fire resulted in 31 people killed and led to fire safety legislation otherwise known as the ‘section 12 regulations’: ‘The Fennell investigation led to legislation that turned fire safety legislation completely on its head, leading to root and branch review of safety culture. It still informs a lot of what we do today.’

Martin said that although not all Fennell recommendations had been carried out, LU was satisfied that it had done as much as it reasonably could, spending millions on fire safety improvements which had resulted in some of the toughest fire safety requirements in the built environment.

Prevention has always been the key focus for LU, which sits alongside the highly-trained capabilities of station staff. Regular inspections are undertaken by the London Fire and Emergency Fire Planning Authority.

LU has standards and verification processes it has developed in-house, which include strict procedures on signing off any works affecting fire protection assets.

‘We have a unique approach to comply with fire safety legislation. If you walked into an LU station you would not find a fire risk assessment document because we don’t have them. We have risk assessments that consider the risk of fire, and which draw conclusions as to whether it is an acceptable risk.’

LU’s challenge is to cope with 21st century passenger expectations with 19th century infrastructure that doesn’t comply with established codes of practice of fire safety in buildings. ‘I must stress that this does not mean we are not safe, it just means we have to find other ways to achieve acceptable fire safety, which we do.’

Some challenges include the fact that some stations have only one way in and one way out, with no secondary means of escape. Some deep stations only have single-user spiral staircases with 100s of steps.

LU’s focus on prevention translates into keeping stations as combustible sterile as possible, as well as having strict controls on the fire safety performance of materials.

Arson is a regular but infrequent occurrence that normally fails as a result of the fire safety materials and the high CCTV coverage. ‘We control flammability, smoke and toxicity – and the last two you won’t find anywhere in mainland UK buildings. The only places you will find that type of control are on ships and aircraft. We do it in a built environment.’

The same applies to rolling stock tests and criteria, reflecting the risks posed by the confined environment and limited means of escape.

No fire detection systems are installed within public areas due to the lack of appreciable fire loads and because there are present either members of the public or staff to detect any fires. But detectors do exist ‘back of house’ with fire suppression in high risk areas including beneath escalators. Emergency plans also exist to evacuate staff, passengers and contractors without the aid of emergency services.

Summarising the LU fire strategy, LU uses strict fire prevention with strict limits on fire load, and relying on early detection and warning of fires. Voice alarm and fire suppression systems are installed in targeted locations, and there are high levels of staffing at subsurface stations. ‘And we have as backstop our engineering aspects covering standards, maintenance and renewal of systems,’ said Martin.

Fire strategies, modelling, simulation and computational fluid dynamics: Tom Kardos, Lead Fire Engineer, London Underground

Tom focussed on fire strategies, tools for fire strategies and how LU develops these – along the way outlining some concerns.

The whole purpose of the fire strategy is to understand the requirements of a fire safety perspective at an early stage of the design process: ‘So that that design is influenced by the fire strategy rather than have the fire strategy justify a design that has already been made.’

All fire strategies primarily address life safety, but there are also key requirements in protecting specific assets which – if lost – could impact on when the railway could be back in operation. This particularly applies to modern signalling equipment rooms which contain diverse systems.

After outlining some of the standards and railway safety principles (and guidance) that LU is subject to, Tom described LU’s project work cycle, which includes the preparation of a fire strategy at concept design, stages of completion, and then future maintenance. And if there are changes further down the line the cycle begins again: ‘They don’t gather dust.’

Tom’s advice to those devising fire strategies was: ‘Keep it simple. If the fire strategy reads well I’m not going to ask questions – it needs to tell how the design works. It tells a story, for example in how a person with reduced mobility evacuates a station.’

In terms of tools for supporting fire strategies, LU has invested heavily in crowd modelling and uses Legion Software for virtually all its work on new station layouts/crowd circulation.

Track record, reaction-to-fire properties of cables and associated equipment used in the sub-surface environment: John Carter, Materials Engineer, London Underground

John’s presentation focussed on safety critical equipment and equipment that is operational and has critical impact on the operation of the railway, particularly as regards materials which are not compliant but have to be engineered in such a way that fire compliance is achieved.

London Underground has very specific requirements to reactions to fire, flame spread, smoke and toxic emissions covering all equipment and systems used in all locations sub surface. These dictate virtually all the designs for signalling equipment, rolling stock and sub-surface stations.

There are often other important safety critical parameters to design systems, such as electrical and mechanical integrity – often vital to avoid the possibility of derailment or collision on the railways.

A series of design case studies where presented showing the oft-conflicting fire requirements and how they had been accommodated into kit now used on LU. One related to signalling cabling, probably the most safety-critical system on the underground, whose failure could have negative consequences. ‘Such cables are often loomed together, representing a very localised fire load, with the system integrity depending on insulation. And what we don’t want is false feeding of signals between circuits.’

The solution arrived at by LU uses a dual-layered composite insulation construction, with the inner layer typically consisting of a tough electrical insulating material, and an outer layer filled with flame-retardant elastomeric polymer.

The inner layer provides the majority of the mechanical/electrical integrity, plus the resistance to longer term chemical degradation effects. The other provides the required reaction to fire performance for underground locations. The use of the elastomer as opposed to thermoplastic means the outer layer doesn’t melt.

Following further case studies and examples of cable degradation in the context of attaining fire compliance via meeting fire requirements, John moved on to compartmentation.

‘There are two methods of reaching fire compliance; first is meeting fire requirements, the other is putting in place adequate fire protection, which can take the form of detection and warnings, suppression, compartmentation – or a combination of all three. And for complex systems like trains or even multiple electrical cables, compartmentation is usually the way that fire compliance with a system as a whole is achieved.’

A compartmentation fire resistance test carried on the back cab wall of the new S-type rolling stock was shown.

The novel nature of the materials used by LU was then touched upon. These materials often don’t fit into categories under national or EU standards, whether they be fire-reinforced composites used on seats, to gels, oils and gases on electric switch gear.

The increasing use of electronic systems used below ground require large scale battery installations as back up for uninterrupted power supplies, and John spoke at length about the specific fire assurance challenges presented by these types of installation, which can involve lead acid batteries, which if overcharged can produce flammable gas. Solutions include 1-hour rated compartments and alarms to monitor battery charge.

LU’s ongoing fire standards development was then outlined, which generally entails comparing the parity of existing and proposed test methods and developing tests geared towards novel kit being installed.

Test results between new EN and original BS standards are fed into the UK’s national standards committee, and one such test was shown involving the new train seats for the 2009 Victoria Line. ‘The test detail is specified in BRE45545 part two, which is the draft European harmonised fire standard for rolling stock. The test was contrasted with comparable test data from existing British standard BS68853, which is specified in our in-house standard.’

LU usually prefers to test complete fire assemblies rather than individual parts, which often involves relatively large samples. LU currently uses a 3m test cube and the results are then scaled up to an actual train, tunnel or underground environment, but LU is currently looking at new test methods to better suit such tests.

In case of fire – a comparison of different approaches to the resilience of rolling stock: Malcolm Dobell, Head of Train Systems and Permanent Way, London Underground

Malcolm commented that LU had put much work into reassuring London Fire Brigade (LFB) that LU felt as passionately about protecting passengers on trains as LFB felt about protecting them on stations: Malcolm’s presentation was focussed on standards and how the new open gangway trains (S-stock) defied all of them. After showing some fires on trains around the world, Malcolm set out to disprove the widely-held view supporting the following equation: small fire + time = a big fire.

Clearly LU cannot completely avoid non-combustible materials, and previous speaker John Carter had already mentioned what had been done in terms of compartmentation to restrict O2 supply. Smoke as a result of underframe fires for example even though on the exterior of a train can still enter a compartment and there is the additional factor that it cannot be diluted in the same way as a normal building. ‘You can’t get people out in a hurry so we have to make sure if something does happen that it happens very slowly.’

Fire has to be put into context of risk, and depending at whether one looks forward or backwards at LU’s history there are different risks. ‘If you look at LU history the things that affect fire risk on the underground are in the order of collision; derailment; arcing; passenger accident; and fire. So fire is comparatively low but we know that if a fire happens the consequences are terrible.’

Malcolm ran through some of the fire risks and the mitigation that had been put in place (compartmentation, alarms on trains etc), including some comment on the decision to take fire extinguishers out of saloon cars. ‘Our fire risk assessment showed that they were causing more harm by having them there than by preventing harm, as they were used as weapons or let off by vandals.’  Today they are kept in the drivers’ cabs: ‘The principle we took at the time was that any fire that could be fought by the typical train fire extinguisher would go out on its own if left alone. That took a bit of effort and persuasion.’

This led to some comment on LU’s work on flame retardant materials and the influence of its work on both British standards and the upcoming prEN 45545. ‘Most of the things we hold dear have found their way into this new standard, except for seat performance – the seat performance we would expect for this standard was lamentable. The tests now done to compare our seats with those that would meet that EN standard are showing that in a graphic way, and we now have the opportunity to influence the standard before it comes into force.’

Going back to firefighters’ concerns of a fire pulling into an underground station, Malcolm showed tests carried out over 10 years ago to counter these.  These tests involved eight number seven wooden test cribs strapped onto the seat upholstery (wool, nylon, fibreglass) of a train. ‘After a period of time the fire went out because the cribs’ wood was used up. And that was not a surprise to us but the fire brigade was bowled over because they were expecting the whole vehicle to be involved.’

After another case study focussing on work carried out by LU into arc protection, Malcolm talked about where LU is today. Many trains now have CCTV and it may not be a coincidence that the number of fires started by vandals are reducing year on year. All new trains meet the code of practice outlined by BS6853cat1a, but the issue of the new open gangways of the S-stock is still to be addressed. ‘BS6853 doesn’t so much specify a fire barrier as imply one, but the standard also says that open gangways are beyond the scope of the standard and need to be subject to further analysis.  So we worked very hard to develop a fire strategy that we could justify as equivalent.’

The importance of assurance in cable specification and procurement: Ian Watts, AEI Cables.

Ian’s presentation raised the alarm that there were growing volumes of non-compliant cable in the UK, partly as a result of the higher costs of raw materials which have seen copper reaching £6,500 ($10,000) per tonne.

It is very difficult to identify a non-compliant cable and it is estimated that 20% of cable in the UK supply chain is of either unknown origin, unapproved or counterfeit. ‘That is quite scary and some people say this figure is an underestimate’. The latest related and available fire statistics (2003-2007) showed that 26-27% of electrical fires were directly attributed to cables. These led to 15 fatalities and 1,200 non-fatal injuries, mainly in domestic settings.

Ian then presented images of defective cables, provided by the Approved Cables Initiative, some obvious, others latent. ‘This armoured cable found in the UK marketplace had 35mm marked on the sheath, but in reality there was insufficient steel armour which was also inadequately galvanised and corrosion was evident; worse than that the conductor was more like that of a 25mm cable. We need therefore to review the level of checking that occurs through all construction phases that would pick up anomalies in cabling.’

More worrying still was the discovery in 2010 that non-compliant cables had arrived in large volumes. BASEC (British Approvals Service for Electric Cables), which is responsible for certifying cables to British Standards, suspended and subsequently cancelled the licence of a company due to insufficient copper. This involved a staggering 11 million metres of cable – unprecedented in the industry. ‘Investigation found subsequently that the cable production affected 2009 as well as 2010, and so we’ve conservatively rounded it up to around 20 million metres.’

To counter the threat, the Approved Cables Initiative (ACI) was set up by UK Government administration in March 2010, widely supported by electrical industry trade bodies. ‘But there are sensible strategies that companies and individuals can follow. The ACI website gives cable marking guidance and a guide to the ordering of cable.

‘So what should you do to protect yourself? First of all you should require the use of approved and certified cable. Always refer to the standard number for the correct application, and use a trustworthy supplier. One I particularly like is to specify cable where you could achieve an audit reasonably easily. Always verify current approvals data, and don’t rely on ‘equal and/or approved.’

Unfortunately in the real world people can make substitutions, take decisions and claim to be unaware of the consequences. Design engineer’s specifications are made by qualified people who will have made a considered choice based on experience and knowledge on behalf of their clients. In summary it is for all of us to exercise vigilance wherever in the construction process we operate, personally auditing products against our expectations and that of the design.’

The future - integrated fire detection and emergency lighting: Paul Turner, New Business Manager, Hochiki.

Paul’s presentation covered legislation and standards covering both fire and emergency lighting, the benefits of integration and a glimpse of the future.

Hochiki’s relationship with LU goes back 30 years in terms of fire detectors. The company has also installed 6-7,000 detectors in St Pancras station (see below) and other stations on the HS1 line (aka the Channel Tunnel Rail Link).

Because of their knowledge and experience in railway infrastructure projects Hochiki is also a partner in the EU-funded ‘Project Getaway’, which will involve  generating simulations to enable testing of alternative routes to improve wayfinding in evacuation of underground and overground terminals.

After outlining some of the standards relating to emergency lighting (BS5266, EN54) and their compliance requirements in the UK, Paul commented that the emphasis today is on issues related to energy efficiency, which current systems do not provide.

The integration of fire detection and emergency lighting is now possible because intelligent fire detection systems are becoming more and more intelligent and intelligent emergency lighting is also now available. With both systems operating on 24Volts and utilising the same communications protocol,  it means the two systems can be integrated, with the emergency lighting system batteries being charged whilst fire is in its quiescent state.

In the event of fire activation, the emergency lighting system will come on automatically, with all the power necessary to drive inputs, outputs, sounders and beacons available from the same system.

Systems can be complex or simple, incorporating exit signage that can also stop personnel from entering specific areas of danger via LED crosses.

This level of sophistication is not available yet, but Hochiki is expecting to be able to deliver this type of system – including a combination of smoke, multi-sensors, sounders, beacons, exit signs, low level lighting, and call points, all on one system, in the next six months.

Asked about the impact of such as system on battery life, Paul pointed out that each of the individual lights had a standalone battery capable of providing light for three hours minimum, and which are continually trickle charged on a loop by the panel. As to the maximum number of devices on a loop, Paul said that most systems today could take 127 devices, and this number would remain the same in terms of a combination of fire detection and lighting devices.

Discussions also ensued on the manual intervention capabilities – eg by the station controller – of such an integrated and complex system, and Paul commented that this would be entirely possible and one of the aspects studied by Project Getaway.

Martin Weller, Principal Engineer (Fire Safety) for London Underground, interjected to say that this type of technology had a definite role to play in buildings where people had to make a decision of where to evacuate and where the wrong decision could lead them to an area of higher risk. ‘Whether it is the right system for an underground station or railway station I’m not sure, and that is why we are also in this project. If the demonstrations show that they work and that they make us more safe – and it is cost effective – then we’ll think about putting them in.’

  • Operation Florian

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