Delving into the deep: Firefighters’ tunnel fire challenge

At about 08:30 on the morning of July 26, 2011, firefighters from South Wales Fire and Rescue Service were called to report of a lorry fire in the middle of the westbound bore of the Brynglas tunnels between June Junction 24 and 25 of the M4 in Newport, South Wales.

Six crews attended the fire from central south Wales and it was extinguished within a couple of hours. The impact on the local transport network was, as can be imagined, very significant and the tunnels themselves were closed for two days with a contraflow being used through the surviving eastbound tunnel. The westbound tunnel opened on July 29 with a 30mph speed limit imposed until deemed safe a while later after using nocturnal repair teams to undertake significant remedial measures to the structure and road surface.

In 2017, David Cameron described the Brynglas Tunnels as a “foot on the windpipe of the Welsh economy” due to it being the major route into the industrial heartlands of south Wales and illustrates the importance of these key elements of the transport infrastructure to the UK.

Built between 1962 and 1967 by the civil engineer Owen Williams (responsible for the old Wembley Stadium, the M1 and the Gravelly Hill interchange on the M6 – also known as “Spaghetti Junction”), it was the first tunnel on the UK motorway network. The twin bore, dual carriageway tunnels were 360m long, a relatively minor tunnel network compared with some of today’s, but does illustrate many of the difficulties that can occur when fire breaks out in a confined, hazardous situation.

Existing, emerging and future technologies used in the tunnel design and construction and, more specifically, by firefighters, have the capability to prevent and control fires more quickly thus minimising the economic and life safety risks for the community when these building blocks of the critical national infrastructure are compromised.

Hazards

The most reasonable worse case scenarios within tunnels are likely to involve a combination of a large fire, a serious, multi-vehicle crash, possibly involving trapped persons and potentially with hazardous material involvement. The hazards associated with tunnel fires on roads are all well-known. Obviously, there is the issue of limited access both to the incident itself (because of tailbacks that can in some circumstances lead to several miles of traffic jams by the time the first responder arrives) and also to get sufficient firefighters to the incident itself on their arrival at the tunnel entrance. At 360 metres, the Brynglas Tunnels are challenging enough with a maximum penetration distance from the nearest entry point being 180m. However, there are many longer road tunnels in the UK including the Clyde tunnel (762m), A55 Conwy tunnels (1,080m), Tyne tunnel (1,696m), the Hindhead Tunnel in Surrey (1,830m), Queensway Tunnel and Kingsway Tunnels in Merseyside at 3,237 and 2,483m respectively. The controversial proposal for the Stonehenge Tunnel near Avebury, Wiltshire, at 3.3 kilometres would be the longest road tunnel in the UK (and at the current rate of progress will have taken longer than Stonehenge itself to complete!).

The distances involved mean that that any incident within the tunnel is likely to have a significant physiological effect upon firefighters as they make their way to the incident location before they begin to make their intervention. In some of the longer tunnels, access by fire appliances from the unaffected bore to cross-over passages (protected passages between two bores that act as an access point for firefighters and emergency responder from the unaffected bore) will reduce distances and the level of physical effort required by responders.

The level of smoke within tunnels can also create challenges, particularly in smaller tunnels. A typical heavy goods vehicle can generate thermal outputs of over 30 megawatts producing sufficient smoke and gases, if not ventilated naturally of mechanically, to obscure and impede access for firefighters, and, critically, evacuation of drivers and passengers in vehicles. Where fuel tankers or high fuel load vehicles are involved the thermal output can be even greater.

“This Mont Blanc fire, which remains the world’s worst road tunnel fire, helped identify several key lessons which helped improve tunnel safety across the globe and in the UK”

Mont Blanc Fire

The Mont Blanc tunnel fire on March 24, 1999, claimed 39 lives when a Belgian lorry carrying margarine and flour stopped near the middle of the 11.6km single bore tunnel, made of concrete, which had very limited fire protection and no sprinkler system.

The profile of the tunnel had a working width of 7m and a maximum height of 7m, which immediately began radiating heat back down onto other vehicles which caught fire, in turn releasing fuel that created a running fuel fire which spread the fire even more widely. As the fire took hold, smoke was moving down the tunnel at speeds reported to be quicker than a person could run.

The smoke plume characteristics during long tunnel fires involve a reduction in the smoke layer height as it drifts further away from the fire itself and reduces survivability of those escaping. The fire caused the oxygen in the Mont Blanc tunnel to be depleted to the extent that vehicle engines stalled, including responding fire engines and led to firefighters to seek safety in the refuges, positioned every 600m in the tunnel. After five hours, they were rescued by another team of firefighters who made their way down a ventilation shaft. Fourteen firefighters were injured and their commanding officer died. The smoke travel had also been exacerbated by natural ventilation from the Italian side of the tunnel augmented by the PPV fans. Ten fatalities had occurred as a result of being overcome by smoke as they were running from the fire. The fire burned uncontrolled for 53 hours.

Mont Blanc Lessons

The Mont Blanc fire, which remains the world’s worst road tunnel fire, helped identify several key lessons which improved tunnel safety across the globe and in the UK.

The first was a need for adequate protection for travellers in tunnels through the provision of cross passages into unaffected bores or fire safe refuges where evacuees can remain in places of relative safety until the fire is extinguished. Automatic detection systems using heat detectors and video surveillance connected to one or more command and control centre was seen as essential to controlling traffic movement into and out of the tunnel.

Smoke extraction and a sophisticated system of smoke management should be incorporated into the fire safety strategy of the tunnel. In Mont Blanc itself, post fire, the tunnel walls were clad in stainless steel to improve structural integrity, with concrete lined pressurised emergency shelters installed at every 300m which included a link to a separated safety corridor parallel to the main tunnel. Finally, the central command and control centre (they installed three centres) housed a 24/7 firefighter team.

As a result of the Mont Blanc and the 2001 Gothard tunnel fire (11 fatalities) the European Union published Directive 2004/54/EC on ‘minimum safety requirements for tunnels in the Trans-European Roads Network’ (TERN) which applies to new tunnels over 500m. The UK Road Tunnel Safety Regulations 2007 Statutory Instrument No. 1520 (RTSR) (as amended 2009) is the enactment into UK Legislation of this Directive. The minimum safety measures are set out in article three and Annex I and include setting the number of bores by expected traffic volumes projected at least 15 years ahead and includes the restrictions of gradients of not more than five per cent (and additional safety measures where the gradient is greater than three per cent).

Research and technology is the foundation of the safety measures in many cases. Where there is no emergency lane, emergency walkways are required (unless it is impractical or costly to do so); there needs to be provision of emergency exits for tunnel users; the banning of shelters or refuges without access to open air is required unless other safety measures including ventilation are assessed to be adequate (but are mandatory in new tunnels where traffic volume is higher than 2,000 vehicles per lane). The distance between emergency exits should not be more than 500m and where these access the other bore, the construction is required to be fire and smoke resisting.

Cross connections for fire and rescue service use should be provided at least every 1,500m. There are other requirements relating to fire resistance and collapse prevention, lighting levels – both normal and emergency lighting – directional/wayfinding systems. Mechanical ventilation systems are required in all tunnels longer than 1,000m and where volumes exceed more than 2,000 vehicles per lane.

Emergency stations with communications facilities and fire extinguishers should be sited at 150m in new tunnels and hydrant intervals should not exceed 250m. Video surveillance and vehicle movement detectors should be installed in all tunnels with a control centre.

Tunnels without control centres should have automatic fire detection systems installed to activate smoke systems which are separate from the pollution control ventilation systems. Traffic control systems should be installed where the tunnel is longer than 1,000m. Critically, radio rebroadcasting equipment for emergency use must be installed in all tunnels over 1,000m long and with traffic volumes more than 2,000 vehicles per lane.

The Directive also sets out standards for pre-planning and the transport of dangerous goods. At the moment, the only Post-TERN tunnel complex in the UK is the Hindhead Tunnel and the Stonehenge Tunnel would meet the Directive criteria apart from the fact neither are part of the Trans-European Road Network (TERN). While the TERN does not apply to the Hindhead Tunnel, its principles have nonetheless been applied as they are considered to be best practice. Whether the Stonehenge Tunnel applies these standards is as yet unknown, but a similar level of protection is expected.

From a technology perspective, new tunnels should be robustly constructed and filled with safety features which can now include thermal imagery, sometimes sprinklers and state of the art communications networks.

Tunnel Firefighting

As far as firefighting within tunnels is concerned, the technological advances over the past couple of decades have transformed the way responders manage incidents. Mobile and fixed thermal technology now provides “eyes on” rather than relying on temperature readings to locate the seat of a fire. Extended duration BA (EDBA) permits deeper penetration of sub-surface structures, allowing more time to search and work within inner cordons. For casualties, survivability could be enhanced through the provision of smoke escape hoods within tunnels (possibly kept in emergency installations or as part of the tunnel safety management system). This would permit evacuation of road users in the event of heavy smoke production or indeed to allow the trapped to remain safely in cars while their rescue is being undertaken. The improvement in interoperability between the fire and rescue and ambulance services, particularly with the introduction of the Hazardous Area Response Team (HART), allows for integrated casualty management and extraction, even in the most hazardous situations.

There have been fires where the fans which are part of the emergency ventilation systems have failed and led to complications. Most systems, along with suppression and detection systems have redundancy built in in some cases but not always. There have been moves in some European countries for the FRS to be equipped with portable fan units to provide emergency ventilation both as a back-up for failed ventilation systems and also for providing air flow in smaller tunnels. Given the relatively low number of long tunnels in the UK compared to countries such as Austria, Switzerland, France and Norway, investment in high volume fans specifically for tunnels is possibly not something FRSs have the finance to resource at this time.

Technological Challenges

As far as management of the incident itself goes, getting the all-important eyes on an incident can now be assisted through the use of drones. Improved wireless communications networks now means that small video drones can be operated from a vehicle cab (or even from a mobile phone) and imagery of the incident can be seen live by the incident commander. Suitably ruggedised drones can even be used to fly through smoke or at low level and into the clear to identify access and egress routes, locate casualties and assess the incident without exposing firefighters to excessive risks. Where the fire is extreme, the use of robotic firefighting will enable sustained attacks on tunnel fires, limiting exposure of firefighters.

While the technology to improve the safety of road users and firefighters in tunnels is developing all the time, vehicle change is also accelerating. Within a decade, petrol and diesel cars will be an historic form of transport, consigned to the past and electric, hydrogen powered cars will be the norm. Even hybrids will no longer be part of the UK transportation solution.

While fires may be fewer, less intense or extensive due to the nature of the lower carbonaceous loading, other risks associated with newer materials used in battery construction will arise. Driverless technology will also revolutionise lives providing a more restful means of getting from A to B but could come complete with new emerging risks to other road users including driver complacency and over-reliance on systems which sometimes fail. Undoubtedly, most of the problems of these systems and vehicles have been identified and controlled but Murphy’s Law will still apply and the FRS and other emergency services will still need to plan for the unforeseen.

The world never stands still and it has always been the case that behind every solution or new invention there is a problem waiting to emerge and transportation is no exception: for every ladder up the technological evolution, there is a snake waiting in the wings. And despite all the devices to aid them, the problem still remains that where persons are trapped in a vehicle in a tunnel which is on fire, there is still the requirement to commit crews for extrication and as long as life is believed to be tenable, firefighters – the boots on the ground – will still be expected to be committed to rescues.