Advances in fire safety on the London Underground Network; by Chris Bacon, New Business Manager at Webro Cables & Connectors.
It’s over 20 years since that fateful evening in November 1987 when 31 people lost their lives as a fire broke out at King’s Cross underground station. And in 2005 we saw the shocking 7/7 bombings on the London Underground, which again raised safety and security concerns for passengers.
Although the safety and security of station infrastructure is much improved from that of 20 or even five years ago, testing work is still being carried out to create a safer environment for commuting, plus station upgrade work is ongoing. The testing procedures for cables are now far more rigorous than in previous years and set a much higher safety level for new products.
Obviously, improvements always need to be made and reviews and revisions of testing procedures will be carried out, but safety levels are at an all time high and should a fire incident occur today at an underground station, the effects should not be as disastrous as before and passengers have a safer route to safety.
Establishment of Section 12
So, how did we get to the safer environment we benefit from? At the time of the King’s Cross incident the safety regulations were not as comprehensive and standards were nowhere near as strict as they are now. The materials, which were installed back then were the same as those being installed in houses and office blocks throughout the country with no thought as to what might happen in the event of a fire in a confined area.
Plus, it wasn’t the fire itself that actually caused the majority of the injuries at King’s Cross. Some cable sheaths used to contain halogens, such as chlorine and bromine, and when exposed to heat they released smoke, which created dangerous acids or contained poisonous gases, like hydrogen chloride. The smoke created was effectively poisoning people, as the fumes had nowhere to escape to.
Insurance companies have found that more people die from suffocation through smoke than from actual gas poisoning or by being burned. This is due to gases, which emerge from every fire, especially the invisible, inodorous, tasteless and therefore extremely dangerous carbon monoxide. Of course other gases will emerge from fires as well depending upon the kinds of materials being engulfed within the flames.
Cables laid horizontally and not in contact with the main flame do not spread fire quickly. However, cables that are installed vertically burn upwards very fast as the flame is supported by hot gases and an upwards turned air stream, creating the possibility of spreading fire throughout a building very rapidly. This rapid spread of fire can be suppressed by using flame resistant and fire retardant sheathed cables and of course fire arresters between floors.
In a fire, cables will burn, drip and deform and can lose all electrical and mechanical characteristics within minutes, therefore rendering a system useless, unless the correctly sheathed cables are installed.
The arrangement of cables can have a considerable influence on the burning behaviour of cables in fire. A single cable installed vertically will direct a fire upwards but this is magnified many times in the case of bundles of cable. This is a particular issue when the spacing between single cables is similar to the overall diameter of the cable within the bunch. In other words the cables are not held together tightly but are in fact held together loosely. These bunches of cables tend to burn the hardest as they support the “chimney-effect” giving the fire the oxygen it needs to burn vertically upwards very rapidly.
A compact cable bundle behaves in a similar way to a single-cable, as the air cannot circulate freely around the separate cables therefore the spread of flame is not as fast.
Shortly after the fire, a public enquiry was carried out and the Fire Precautions (Sub-Surface Railway Stations) Regulations 1989 – more commonly known as the Section 12 regulations (as they were brought in under Section 12 of the Fire Precaution Act 1971) – were introduced from the subsequent Fennell Report.
Perhaps the most obvious result of the enquiry was that smoking was banned on the underground. On top of that all wooden escalators were removed and mandatory fire safety systems were installed. It also led to fire safety training throughout the network.
Overall the Fennell Report led to a change in culture with regards to fire safety on the underground. Sub-surface rail stations are now referred to as Section 12 locations and all cabling at those stations must now meet the requirements set out in LUL Standard 1-085.
LUL 1-085 covers the fire safety performance of materials used on the underground network to ensure that should a fire break out, it is quickly stopped before the flames and fumes can cause damage to the station or its commuters.
Within the standard, section 3.3.3 specifically deals with the flammability, smoke emission and toxicity and since its introduction in August 2003 has directly and dramatically increased safety across station infrastructure and communications. To adhere to these regulations, all cabling must be subjected to a series of stringent testing processes.
The (BS 50266-24C) flammability test involves bunched cables being vertically mounted and exposed to a flame. The cable bunch is then monitored to evaluate the extent of the vertical flame spread and at what level the flames die out. In order to pass this test the fire must burn itself out before the flame reaches a 2.5m height. This may seem like a short distance but it is essential this is met to ensure the flames do not spread across the station and that vital communications cables – such as for fire alarm and public address systems – are not severed by the fire.
For the smoke emissions (BSEN 50268) test, cable is secured in an enclosed space and subjected to fire conditions while the volume of smoke and the transmission of light are measured. The toxicity (BS 6853B) test primarily checks for halogens, nitrogen and sulphur through qualitative analysis using x-ray spectroscopy.
It is not possible to give definitive parameters for these tests as each cable and environment requires a different level of testing. However, all tests are carried out by UKAS-approved test houses, with all measurements being recorded and submitted as part of a complete test report to London Underground Limited before any cable is given approval.
Products covered by Section 12
Within the underground station communications infrastructure lies dozens of different types of cable networks, such as those for passenger display boards, ticket machines, fire alarms, CCTV cameras, passenger help points and public address systems. All those communication points are key to the smooth running of any station and therefore, in the event of a fire, they need to continue working correctly to aid – and not hinder – the exit of the commuters.
In their simplest form, all approved cables today are much safer due to the increased lifespan under fire conditions and the limited emission of gases. CCTV cables such as H124 Coax will survive for longer periods of time when compared to the old PVC or standard LSZH (low smoke zero halogen) products. This enables control staff to understand what is happening in specific areas and how best to deal with evacuation and overcrowding issues as they arise.
Communication solutions such as data cables for voice and broadband offer the same sort of safety levels and can continue to operate for periods under fire conditions.
Improvements
The level of testing carried out on London Underground cabling before the King’s Cross fire was very low. When the fire broke out, the results were devastating due to there being no stringent processes in place to minimise the spread of damage.
Following introduction of the LUL 1-085, standard cabling is now flame retardant and has zero or low-halogen content, making it more robust when in use and when subjected to fire or damage. But not only that, the safety standards are now so high that there shouldn’t need to be any amendments to the requirements for many years to come.
However, it is irresponsible to suggest that no reviews should be made. It is essential that regular checks are carried out to ensure the ongoing safety of the workers and the commuters on the London Underground, but significant changes are unlikely in the near future.
With the tougher regulations, coupled with new innovations in cabling technology, we are able to make the London Underground a safer system to travel on. In fact, our rail maintenance specialists have been part of the team that has been working to improve station infrastructure and communications across the London Underground network, most notably for the stations at Oxford Circus, Piccadilly Circus, Bond Street, Uxbridge and Tower Hill.
It’s very disappointing to look back and think that it took such a devastating event to cause a shift in thinking and generate the current regulations; however it’s comforting to know that now every time we travel in the capital we’re in safe hands.
About Webro and Connectors
Webro Cables and Connectors has been supplying product to a number of leading railway and transport infrastructure providers for more than 15 years, including the Docklands Light Rail, Network Rail, Highways Agency and the London Underground network, for which it is Link-Up certified and Section 12 approved.
Webro has introduced 20 new security-related cables to its product portfolio so far this year resulting in sales of more than 800km per month with UK security companies. Webro’s portfolio of products now includes those for industrial, telecom, broadcast, radio frequency, high temperature and networking (copper and fibre) usage.
Webro was established in 1980 and is a supplier of composite and bespoke communication cables and connectors. It supplies the top five UK TV and satellite distributors – including the BBC and Sky – and its coaxial cables are used in many systems, applications and industries including top hotel chains and caravan sites.
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