The main concern has naturally been for transport tunnels (rail and road) used by the public with arguably as much attention being paid to protecting the fabric of the tunnel as to removing or protecting the users from danger. While the possible ‘blast furnace’ conditions of tunnel fires make fire the most recognised hazard for the public, the generated smoke, toxic gases and loss of oxygen can easily kill or disable as well, and often before the actual fire is a real threat. Even though statistics show that tunnels are the safest stretches of highways, for example, there are many other potential hazards in tunnels for both professional and lay users. This can only be eliminated or minimised by careful design, operation and planning of emergency procedures.
Norwegian statistics show that the safety records in road tunnels is only bettered by that for high-speed, national roads in sparsely populated areas. In Switzerland the trend is confirmed where an analysis showed the average accident rate in road tunnels to be 0.35 per million vehicle-kilometres compared to 0.47 for open roads.
The more enclosed (and controlled) nature of tunnel operations, which may account for their better safety record compared to open sections, can add to problems in case of hazardous incidents, chiefly by restricting access and acerbating ventilation and lighting deficiencies. The space for rescue, firefighting and escape is limited, and the enclosed structure can trap heat and allow build up of toxins.
Statistical studies have revealed that many of the previous assumptions about the presumed dangers of tunnels are actually myths. Not only are they some of the safest sections of transport routes, the incidence of highly publicised catastrophic incidents and associated loss of life in transport tunnels are fortunately rare (T&Tl Feb, p47) but, of course, unacceptable. Risk management studies refer to these as of the ‘low probability/large consequence type’.
Minor incidents
The occurrence of minor incidents such as vehicle breakdowns and minor collisions with resultant debris are much more frequent. These could all result in worse incidents of collision and fire if not dealt with quickly and properly. The presence of rapid response teams in busy highway tunnels may account for the better record of tunnels overall.
Similarly incidents such as shed loads and spillage, of medium frequency, could cause greater problems. Depending on the materials involved, the latter could have serious implications for the tunnel ventilation system to protect other users from toxic fumes and loss of oxygen, or the material could be highly flammable. The tunnel’s operational plan may include the banning of certain loads therefore.
Rail tunnels generally have a better safety record than road tunnels, but the high density of people in many situations (full trains and rush-hour metros as examples), mean that the potential loss of life from serious incidents could be high. A relatively new, but still fortunately rare hazard, is the possibility of terrorist action, which tends to target crowds. The nature of this threat, being deliberate rather then due to accident or carelessness, demands modification of response procedures and improvements to preventative security systems.
The OECD has a Futures Project on Risk Management Policies, which focuses on the consistency of risk management policies and their ability to deal with challenges created by systemic risks. In its Phase 1, participating countries propose specific case studies for which the OECD Secretariat provides an overview including both the international and national situations. Later, risk management issues will be reviewed in depth if required, and finally a cross-country report will assemble lessons learnt and identify opportunities for sharing best practices and improving risk management.
One of the OECD Phase 1 studies was for Norway on ‘Risk management in connection with the prevention of and response to fires, and to accidents involving dangerous goods in underground traffic systems’ and proposed by the Country’s Ministry of Justice and the Police. Part of the Ministry’s brief refers to the desire to optimise transportation of humans as well as goods when dangerous goods may be present in the same tunnel. In Norway the length and number of tunnels makes it a very worthwhile subject for national study.
The OECD Norway Tunnel Safety study points out that, although rail tunnels are relatively safer, the market share of rail for total freight has been steadily decreasing. This is despite the intermittent efforts of national governments and major freight handling projects such as the Gotthard and Lötschberg base-tunnels. Therefore road tunnels have to deal with the realities of bulky loads being present which often offer fuel for fires and explosions, and perhaps other hazards to life.
Prevention
Lay users cannot be expected to act totally logically under incident stress, so the design of the tunnel must take human frailties into consideration. Recent studies and simulations of behaviour during dangerous incidents have been carried out, but it is very difficult to simulate the reactions of tunnel users under actual incident conditions, even if the physical hazards can be simulated. All the tunnel designer and operator can do is to provide places of safety as near as possible to likely incident locations, and to make the routes to safety clearly recognisable, unobstructed and as well lit as possible.
Unlike rail tunnels, the practical free will of road tunnel users can make the control and direction of their movements a very complex matter, especially if there are multiple slip routes. As a result the assistance of computer control has been widely adopted for both urban and long trans-barrier tunnels. As well as providing routine traffic control, and early indication of hazardous congestion or incidents, the control systems may include control of ventilation, lighting, warning signs and voice communications as well as monitoring and alarm functions.
Lyon-based ISIS, a member of the Egis Group, specialises in traffic management procedures for road and rail systems. Operated from a surveillance centre, the traffic management and operations aid systems are used to:
- Manage road equipment such as variable message signs (VMSs), automatic incident detection, general cctv and video, and lane-closure arrows
- Improve user safety in case of incidents by shortening emergency response and information times
- Optimise the use of new communications media such as Internet, WAP & RDS
Towards these ends, ISIS uses its traffic engineering and control skills to develop system management strategies, draw up specifications and provide system monitoring and development services.
In the rail sector, Pöyry Infra Traffic has, within a joint venture, been developing the railway equipment for the Gotthard Base Tunnel according to the RAMS analysis (Reliability, Availability, Maintainability, Safety) according to EN50126.
Similarly, Transsol of the UK has conducted RAMS compliance assessments for the Athens Metro Line 2 and 3 extensions, and the Channel Tunnel Rail Link (CTRL) telecommunications systems. The Athens Metro Line 2 work included the Automatic Train Supervision (ATS), signalling and Automatic Train Protection (ATP) systems, the train radio system, and all electrical and mechanical plant in the tunnel, stations and depot. On the CTRL, Transsol’s contract included the Global System for Mobile Communications (GSM-R) for train to signaller communications, and also the fibre-optic digital transmission network (FODTN). The latter will carry voice, signalling and video data. In addition there is a remote SCADA system for E&M information (EMMIS) that provides transparent transmission and reporting of data for all electrical and mechanical plant installed on the railway. Tasks include compliance with European Technical Specifications for Interoperability (TSI) for high-speed lines.
Other tunnels
Of course, not all tunnels entered by people are transport tunnels, although those travelling tunnels such as sewers and cable ducts are either trained or are visitors under supervision. Due to the smaller section of such tunnels, another safety consideration will be inclusion of precautionary enclosed space procedures before and during travel including precautionary gas testing. Ventilation is unlikely to be as good as that in transport tunnels as there is less need for heat and fume removal under normal circumstances. Pockets of hazardous gases and/or oxygen deficient atmospheres are therefore possible.
Control systems
The control of tunnel life-support and assistance systems in larger tunnels will be carried out from a central point with the aid of monitoring systems supplying data and observations on which actions and actuation instructions can be based. The control can be manual, automatically assisted or computer-controlled, and it is a subject of considerable debate whether an automatic, usually faster response is better or whether a manual-control approach by a fully experienced operator is better to offer the flexibility to suit changing conditions.
There is little doubt that the maximum in designed flexibility should be available. Although computer simulation makes assessing a large number of fire scenarios more plausible than using only real set fires, an unforeseen set of incident circumstances is always possible. So many assumptions have to be made in design fires that, even if input data is reasonable, it may not all be accurate for an actual incident, although simulations are important to understand the processes involved in underground fires, enabling better control decisions to be made. Factors that will influence the tenability times for a fire include the materials involved, the fire heat release rate, ventilation speed, and the time taken for the smoke management fans to activate.
A control system is useless without data from remote sensors for visibility, gases, smoke, heat, air speed etc., and cctv images and analysis. There should also be facilities for communicating with drivers, whether to provide information on radios, or to receive requests via 2-way radio, telephone or intercom.
Lighting
Under normal circumstances, tunnel lighting has to be designed and controlled to avoid driver distractions such as glare, and to provide a gradation to optimum tunnel lighting conditions from the outside light levels, at day or night. The monitoring and control systems available include luminance and illuminance photometers from Mayer International. The meters provide continuous monitoring and recording of luminance at road tunnel entrances, and automatic on/off lamp switching control. Standards for the lighting of road tunnels are recommended and published by the Commission Internationale de l’Eclairage (CIE) with which Mayer systems comply. The illumination in the tunnel threshold zone is continuously changed automatically to match changes in exterior daytime brightness, thus avoiding the ‘black hole’ effect on drivers.
The Mayer TS-101 luminance photometer uses a silicon light receptor filtered to provide a spectral response close to that of the average human eye, and has virtually instantaneous response to changing light levels. Recently Mayer has developed lighting management units to work with the TS-101 to dim individual luminaries throughout the tunnel as required. The TS-150 illuminance photometer measures corrected incidence light to check that interior illumination levels are being maintained according to specified parameters, and changes of exterior daylight levels as measured by the TS-101.
In an emergency, lighting can be even more important, although it may easily be masked by smoke in the event of a fire. In these circumstances, special lighting to aid identification of exist routes, communication points and firefighting equipment adopt greater importance. Lit matrix signs as warnings or indicators remain important too. Secondary power supplies, unless affected directly by a fire, will provide extra assurance of safety indication. In the event of total power failure, the safety and escape signage will be coloured and reflective to work with portable lighting.
Ventilation
The provision and control of a ventilation system that can cope adequately with all likely or possible emergency situations as well as day-to-day variations is a complex topic and one that has been described in some detail by numerous recent articles in T&TI. Indeed it is a subject of continued research covering topics such as how best to deal with smoke generated (and hence improve visibility and air quality) whilst minimising fire spread and intensity.
Life-saving routes
When firefighters and rescuers become available it cannot be assumed that all will suddenly be well. Depending on the location of the fire compared to the safe base (control point) for firefighting, the distance involved may be too long for the ‘lifetime’ of breathing apparatus. This should be taken into consideration in the design of the tunnel structure with, ideally, frequent cross-passages to a second bore, or intermediate access points for single-bore tunnels.
Portable refuges may be used to aid firefighting logistics, such Draeger’s rescue train shelters. The special escape and rescue standard ISO containers are mounted on railways cars, and can provide accommodation for up to 70 people for up to four hours. Breathing air is supplied from a high-pressure store mounted on the train for safe withdrawal of tunnel users and workers from the effects of the fire. The customised units may also include breathing air compressor, telecom systems and firefighters breathing apparatus.
One of Draeger’s recent introductions for tunnel use is the Parat C Fire Escape Hood, which filters out toxic smoke and fumes, and protects against carbon monoxide from a fire, enabling safe escape with a minimum ‘life’ of 15 minutes. The ‘one-size-fits-all’ equipment has a wide visor with anti-fog coating for clear visibility. Various ‘pack’ designs are available to suit the use including a simple cardboard-box single pack, a soft pack for portability, a protective plastic casing, and a twin-pack wall box for wall hanging and emergency availability.
Flakt Woods jet fans used to control smoke flow and other air contaminants Flakt Woods jet fans TunnelAlert by RadioScape keeps users alert with DAB TunnelAlert by RadioScape keeps users alert with DAB Draeger’s Parat C Fire Escape Hood filters toxic smoke and fumes Draeger’s Parat C Fire Escape Hood filters toxic smoke and fumes Emergency shelters can be easily seen in the Mont Blanc Tunnel with lighting provided by Shréder TMB luminaries Emergency shelters can be easily seen in the Mont Blanc Tunnel Training underway for terrorist attacks at LU’s Bank Station Training underway for terrorist attacks at LU’s Bank Station