Equipment, fire behaviour and operating principles
The technical directive, (appendix 2 of circular n° 2000-63 – in French) applies to new State-managed tunnels over 300m. For existing State-managed tunnels and those managed by local authorities (whether new or not), it serves as a technical reference for defining the level of safety.
- safety equipment,
- fire behaviour,
- operation.
It should be noted that this circular only concerns tunnels longer than 300 metres. Below this length, there is no specific “tunnel-related” issue, as in the event of a major incident, the natural reflex is to quickly reach the tunnel exit, which is nearby.
Safety equipment
Essential safety equipment is designed to address a number of concerns:
Power supply
How can the operation of emergency lighting, signalling and lighting systems, and traffic management equipment be ensured without interruption in the event of a power failure or outage?
How can the necessary power be provided to implement smoke extraction in the event of a power cut?
Ventilation and smoke extraction
How can pollution levels in the tunnel be kept below the thresholds recommended by the Ministry of Health at all times?
What smoke extraction system should be adopted, taking into account the configuration of the tunnel, the volume and composition of its traffic, its environment, etc.? How effective is this system? How reliable is it? How easy is it to implement?
How can the tunnel and all related facilities (galleries, shelters, etc.) be ventilated?
Lighting
How can a minimum level of lighting be ensured in the tunnel and related facilities in the event of an incident?
How can users in difficulty be helped by marking the evacuation route and guiding them to shelters or emergency exits?
The emergency call network
How can we enable users in difficulty to communicate quickly with the operator’s services or the emergency services?
How can we make this call system accessible to everyone, including people with reduced mobility?
Fire detection and fire-fighting equipment
In what circumstances should an automatic fire detection system be installed? What functions should this system trigger?
How can the water flow and pressure required by firefighters be reliably provided throughout the tunnel? How can this be achieved even in the event of a pipe rupture?
Signalling, signage and tunnel closure devices
Signalling has been regulated by the interministerial road signage directive since 2003.
Radio communications relaying
How can we ensure continuity of communications and relay radio communications for emergency services, wherever they are in the tunnel? How can we broadcast information or instructions to users in the tunnel by radio?
Monitoring and rapid incident detection means
How can we ensure that any incident is detected as quickly as possible? What can be automated, given the way the tunnel is organised?
Fire behaviour
A lorry fire is the most feared event in a tunnel. If this occurs, it is essential that every structural element and every piece of equipment can fulfil its function despite rising temperatures and the possible spread of the fire. The following aspects are examined with particular care:
The reaction to fire of materials
How and under what conditions are the various materials likely to contribute to the fire to which they are exposed?
Are the minimum requirements of the technical directive met?
Fire resistance
What temperature assumptions should be taken into account?
What levels of fire resistance are required from the various elements of the tunnel structure, taking into consideration their strategic importance or not in maintaining the structure, evacuating users and implementing emergency scenarios? How can acceptable conditions be guaranteed in the various areas where users or emergency services are likely to be present?
Equipment operation in high temperatures
How can the continuity of the main power supply lines and telecommunications cables be guaranteed, regardless of where the fire occurs? Can the jet fans withstand the rise in temperature for a sufficiently long time? What about their performance? Is the fan mounting system also able to withstand these thermal stresses? Will the operation of each component of the smoke extraction system be guaranteed under the temperature conditions specified by the regulations?
Operation
The importance of operating resources
Given the characteristics of the tunnel, its traffic and its environment, which of the four levels of staffing (call) and surveillance defined in the Directive should be adopted? What are the consequences in terms of the organisation and equipment of the tunnel?
Where are the emergency services located? Are they equipped to respond? What resources should they have at their disposal?
The development of reference documents
How is traffic in the tunnel regulated? Are all vehicles allowed?
Does everyone involved in the safety chain have clear instructions on how to respond to each type of incident? Do these instructions cover all possible causes of incident/failure?
Is the emergency response plan, which must include all information on the organisation and coordination of emergency response resources as well as general emergency response instructions, complete?
Maintaining safety levels over time and capitalising on experience
Are exercises carried out at a satisfactory frequency? How is feedback on incident response procedures provided? Do we have the means to learn from events that occur?