The risk of a fire in a tunnel under construction is minimised by good planning, coordination with the emergency services, procurement of equipment with fire-safety in mind, and awareness of procedures and documentation.
Storbelt tunnel fire
The contract involved two bores, 8km-long, 7.7m ID, 75m below sea level, using four Howden EPBs. The TBMs incorporated twin track within the gantries, and were considered to have advanced fire fighting provisions, including two water curtains, AFFF fire suppression systems controlled by a central control panel housed in a non-fireproof container, and 10 fire reels. The control panel was not in an explosion proof container, so it was not connected to the emergency power supply.
On the morning of Saturday 11 June 1994, around 7.30, just after handover from nightshift to dayshift, there was a large ash around the shove rams. Within seconds the TBM methane alarm, set at 25 per cent LEL and 50 per cent shut-down of power supply, cut the mains power to the TBM. Emergency power systems were activated, and thick black smoke engulfed the TBM.
The well-drilled crew donned MSA sets and gathered at the permanently-available man-rider at the back of the TBM. The TBM engineer and foreman went to the fire control panel but this was inactive as it was connected to the mains supply. They were thus unable to activate the sprinkler system.
Four trained members of the crew donned breathing apparatus (BA) sets and operating as two teams carried out a search of the upper and lower levels of the TBM. Once satisfied all were accounted for, the crew evacuated the TBM. Those working on adjoining cross passages and the second tunnel drive also evacuated to the surface.
The fire crews tried several times on the day of the fire to enter the tunnel. They also attempted to introduce CO2 into the tunnel air mains to contain the fire, but this failed due to freezing. During the day of the fire the ventilation system was shut down. Entry was only possible towards the end of the second day, where it was apparent that extensive damage had occurred to the tunnel lining with up to 200mm spalling of the 400mm thick concrete tunnel lining.
The initial fuel source of the fire was put down to hydraulic oil atomising from a hydraulic ram. The source of ignition was never established.
There were no injuries. The crews were well drilled in emergency procedures. There had been a fire on one of the adjacent machines the previous year, which had resulted in extensive review of procedures. Emergency drills were also emphasised due to the risk of flooding, particularly from cross passage excavation, which was being carried out at the same time as TBM excavation.
Extensive repair work was required following the fire. The site took the precaution of constructing two water-tight bulkheads at the portals prior to repair work, and a third bulkhead to enable compressed air to carry out these repairs.
The fire extended the contract by nine months, and cost USD 33M.
A86 Socatop tunnel fire
The 10km A86 Socatop 11.5m ID tunnel was being excavated in 2002 using a TBM capable of working either in EPB or slurry mode; at the time of the fire, it was in EPB mode. This unique tunnel to the west of Paris was part of the circular road being constructed around Paris. The tunnel was split into three horizontal levels, which were created during construction. Two horizontal slabs were concreted to split the tunnel into three separate chambers: the upper part for the conveyor and ventilation, the lower part for TBM traffic. The tunnel train was approximately 70m-long and was powered by diesel engine. The tunnel concrete separation slabs were being constructed using timber and plywood, which was being installed as the tunnel was being excavated.
During the planning stages extensive review of fire scenarios were prepared, including fires occurring at any of the three levels within the compartmentalised tunnel. The TBM was equipped with a manlock to gain access to the cutterhead; there were fire detection and fire suppression systems, water screens and sprinklers. In addition, the Paris fire brigade was involved with the project, and monthly inspections and training drills were carried out.
On 5 March 2002, at 22.30, one of the diesel locomotives caught fire when situated under the tunnel timber formwork. Four trained men tried to fight the fire. The TBM crew was informed. The TBM crews activated the rear fire-curtain and went to the front of the TBM. As the fire blazed, the tunnel ventilation collapsed.
Communications were lost and the ventilation was switched off. The Paris fire brigade tried but was unable to gain access to the TBM.
Nineteen operatives on the TBM were trapped for nine hours. They did not panic but remained in the TBM manlock as required by their emergency procedures. Within the manlock was water and fresh air. It had subsequently been calculated that there was 48 hours of breathable air supply available to them. Once the fire brigade managed to get through to the TBM, all 19 operatives were safely removed over a three-hour period. There was one injury to a fireman due to falling down through an opening between first slab (ankle sprain).
The 400mm-thick concrete tunnel lining was damaged due to the fire. It had behaved as the designers had predicted if a fire had occurred, with up to 100mm of spalling.
The cause of the fire in the diesel engine was put down to an oil leak to the turbo. Following the fire all diesel locos were changed, the fire suppression systems were improved, and the durability of the tunnel communication systems were improved. The fire plan was revised, training was reinforced, and goggles were supplied with the tunnel MSA re-breather sets.
Fire and smoke suppression systems on the TBM were improved.
The fire brigade
The purpose of the fire and rescue service in law is a responsibility to plan for operational incidents, to carry out a preventative function, and fundamentally to respond to emergencies. In addition to this, following a fire, to carry out investigations into the causes.
The brigade acknowledges that the circumstances when dealing with a fire in a tunnel under construction can often involve additional challenges to its more normal mode of operation when dealing with a fire in the conventional-built environment.
If a fire occurs in a tunnel environment, communications are vital, as is water supply. The lack of ventilation and long travel distances in a tunnel fire places additional stress on a fire fighter. The manual handling consideration can also cause significant physiological effects. For example a single 20m length of water hose weighs 100kg. This is cumbersome, and if a number of lengths are required, will result in a significant resource impact to commence a fire fighting attack, in terms of personnel and BA. Construction sites present challenges, which can be overcome with proper planning, preparation and communications, particularly on arrival.
A fire fighter in full gear relies on BA and on integral communications, which are intrinsically safe for hazardous environments. In the past, contractors have wanted to issue hand- radios to the fire fighters. This presents problems. It takes away one of their hands for a start. Heat stress can have detrimental effect and thought processes become more difficult. Tunnels are enclosed and in an emergency situation can be very stressful. A dedicated radio channel for the emergency services does involve additional cost, but it is fundamental to how the emergency services are able to operate efficiently.
Water supply is also crucial, and history has shown that if enough water is available, the fire will eventually be put out. It is also important to minimise the amount of combustible material permitted within a tunnel environment. The heat that can potentially develop in a confined space is immense, and can make conditions intolerable for human activity if combustible materials are not properly managed.
It is vital that upon arrival the fire service are given current, accurate information. This includes the number of people involved, the best access to the incident, including any newly construction points of access, newly constructed shafts and cross passages, smoke curtains, fire suppression systems, the location of any refuges and bridgeheads. This information can make a crucial difference to decisions that need to be made by the incident commander.
A key requirement is a responsible person who meets the fire crew on arrival, and can assist the incident commanders in making decisions, based on a dynamic risk assessment. The better the information made available, the better the decisions that are made. If there are lives to be saved, a higher level of risk will be taken by the Fire and Rescue Service, but without lives at stake, less risk will be taken.
During the planning stage it is important for the contractor to work with the Fire and Rescue Service. It ensures information is given to local fire stations so site-specific plans can be prepared and initial plans are in place. This gives the fire crews a vital head start when they arrive at an incident. This should be considered an on-going process where any significant change to access or response facilities should be communicated the service.
The overall responsibility for the rescue does sit ultimately with the brigade’s incident commander, but incident management is a team response and the responsible person has an important role to play.
Also vital is how many people are within the tunnel. Increasingly more complicated systems are being used to record the number of people underground. How readily available is this information? Is it kept at a central location? Can it be made immediately available to the incident commander? If lives are at risk it makes a huge difference to decisions the incident commander has to make.
On large contracts, it is a good idea to have one point of contact within the brigade, as the person who will develop fire and rescue policy. On larger projects it is a good thing to have a standardised policy for levels of fire protection, and also controls to be put in place and emergency procedures when dealing with an incident.
Flammables and cylinders present particular issues. The brigade no longer close down large areas of London when a cylinder is alight, but acetylene in particular will lead to an area being closed down, due to the risk of explosion. It is recommended that a tally system is put in place when cylinders are in use, and in the event of an evacuation, to try and get the cylinders out.
One other observation is the human element of barriers between contractors. The brigade will try to overcome these personality issues, but where they cannot, they will escalate the issue to the client. The brigade is always keen to develop good relations.
The fire and rescue services have a national incident command system. The contractor’s responsible person will be an equal partner in this system. On arrival, the brigade requires quality information to base their decisions on. This contractor’s responsible person should be easily indentified, so the brigade can trust the level of information being supplied. This person then forms part of the brigade’s response team.
Donald Lamont – animateur ITA WG5
There are three things that have to come together to make a fire; oxygen, ignition and fuel. In tunnelling the only thing you can control is the fuel. In a tunnel fire the flames will hit the crown of the tunnel and move along horizontally. A plume of smoke will also travel horizontally. Initially the smoke is hot, buoyant and turbulent. In certain tunnel fire situations there may well be a separation in the tunnel between both smoke and flames in the top half, and fresh in the lower half.
In terms of heat output, it is important to appreciate just how much radiant heat can be generated from a vehicle fire. The heat from a car on fire will be somewhere between 2 and 5MW. A large vehicle fire could generate between 10 and 20MW of heat. You cannot get close enough to this heat source to fight this fire with hand-held extinguishers.
It’s not just the radiant heat that you need to look at, but also toxic smoke. In a tunnel environment that toxic smoke will travel along the tunnel, and can affect both your breathing and eyes if you don’t have a pair of goggles.
There are lots of fuel sources in tunnels: Vehicle cabs, rubber tyres, hydraulic fluids, lubricants, grease, diesel, hydraulic hoses, cables, lubricants, cables, conveyor systems. They all can burn in the event of a fire.
Good housekeeping is particularly important. Rubbish is fuel. Store it in fire-resistant containers and remove the rubbish as soon as possible.
Electricity at 3.3kV to 11kV has a high potential for sparking to form a source of ignition. Other sources include internal combustion engines, friction, impact, and hot work. Another concern is smoking, which is banned in tunnels, but occasionally traces can be found. Fires do occur underground.
CDM regulations part four sets out requirements for the contractor to take in to account. Designers should also be aware of the requirements, so designs can be tailored to make it easier for the contractor to comply. Reg 38 talks about preventing risk from fire. Reg 39 talks about the need for emergency procedures, Reg 40 the need for emergency egress routes, Reg 41 fire detection and fire fighting requirements.
In terms of the policy from the HSE, fire has low probability but high potential consequence. Fires don’t happen very often, but when they do, they have high impact. Fire fight to save life only, don’t commit when lives are not a risk. Don’t put fire fighter’s lives needlessly at risk.
The principal object is prevention of fire occurring; the second objective is not to put lives at risk needlessly.
One of the characteristics of a hydraulic oil fire is the rapid build up of heat and smoke. The tunnel owner should impose a fire risk reduction strategy. All significant items of underground plant, either mechanical or electrical, should have an onboard fixed fire suppression system. You hit the button, and then you go. You don’t stay and fight the fire.
Hydraulic oil should be low flammability hydraulic fluid. Note that its fire resistant properties decrease with In terms of heat output it is important to appreciate just how much radiant heat can be generated from a vehicle fire time. Don’t forget the local plant hirers. Make this requirement known to them. It is good practice to run a system where vehicles must be authorised before they are allowed in to tunnels. This may be controlled by the use of vehicle signage.
In terms of European Standards, the current requirement, EN12336 will be replaced by EN16191 in 2013. They both have requirements on fire protection. Tunnel machinery shall be designed to avoid the risk of fire. Also, all machinery shall be equipped with fixed fire suppression systems.
In addition, portable fire extinguishers should be distributed along the TBM, with a water curtain at the rear.
BS 6164, section 13 deals with fire and smoke. 13.4.3 refers to fire extinguisher systems. All underground machinery should have fire extinguisher systems covering engines and tyres. BS 6164 also talks about conveyors (low flammability materials), cables (again low flammability), and electrical systems, which should have fire extinguisher systems.
Section 14 deals with response to emergency: the need for emergency control rooms, rescue capability, communication systems, accounting for underground personnel, alarm systems, self rescuers, refuge chambers and for emergency exercise drills. It’s all very well making emergency plans, but they need to be tested in a planned manner.
Refuge chambers have all of a sudden become very popular. There is a clause in BS 6164 and also in EN 16191 but they give relatively little detail on the requirements for chambers. Where the risk assessment shows the refuge chamber to be necessary, then it has to be provided. However the ITA is drafting much more detailed guidance that is due to be published in the spring of 2013. This will explain that the requirement for a refuge chamber will be based upon risk assessment. The presumption will be that you provide a refuge chamber during tunnel construction, unless the risk assessment shows it to be not necessary.
It is to be emphasised that a refuge chamber is not an alternative to escape to the surface. The first preference is escape to the surface. A refuge chamber does not provide protection from fire or flood. It doesn’t provide protection against collapse either. It is not a structural chamber.
A benefit of a refuge chamber is accounting for personnel without committing surface personnel entering the toxic atmosphere to carry out a rescue; the personnel are accounted for and are in communication with the surface rescue teams.
There are three operational modes; standby – no incident has occurred, the chamber is unoccupied, but is ready for immediate use; externally supported – an incident has occurred, the chamber is occupied, and the chamber is supplied from a surface air supply, via a tunnel compressed air line. Effectively you then have an infinite supply of breathable air, as long as the surface air supply and the tunnel air line are maintained; standalone mode (the trickiest mode) – an incident has occurred, the chamber is occupied, and external power and/or external air has been disconnected, and now the occupants rely on the chamber for life support.
This includes a breathable atmosphere, air cooling, lighting, communications and water. The ITA guidance will require the refuge chamber to be able to operate for a minimum of 24 hours in this mode.
Refuge chambers are complex to operate, particularly in standalone mode. Personnel could die in the chamber if it is not operated correctly.
The chambers can heat up and the levels of CO and CO2 can build up.
Questions from the floor
Online: Is there a formal contract between the contractor and the fire brigade?
David Bulbrook: there is no formal contract. The fire brigade are obliged to provide advice to the contractor on how they will respond, and it is in their interests to provide this information.
Nigel Valvona, Thames Tidal Project: For very long tunnels, how many refuge chambers should be installed?
Donald Lamont: You should give some thought to where the fire is likely to occur. For a long tunnel, you will be looking at protection around the TBM. In between the TBM and the pit bottom, possibility only the train and the locomotive are a potential fire source. Bear in mind that for a tunnel fire, the ventilation will drive the smoke out of the tunnel. Self rescuers will also be available, and there may be a requirement to provide stockpiles of selfrescuers along the tunnel, to provide escape to the surface.
Clive French from Alliance Insurance: You mentioned the Fire Brigade has a statutory right or duty to investigate after a fire incident has occurred. How long would such an investigation last after the event has happened?
Dave Bulbrook: That it depends on the complexity of the fire, and that if the fire involves a serious injury or death, the investigation will take longer. It is a very difficult thing to quantify exactly how long the investigation will take; it very much depends on the circumstances of the fire. There is no simple answer to this question.
David Hobson from Jacobs: There has been a lot of work been carried out in London on Crossrail and Tideway developing good fire plans, and looking at the risk assessment. Is there any possibility of getting such plans onto the BTS website so that others can use them as examples of good practice?
Damian McGirr: That this may be a possibility, if the plans are made available.
