By Dave Hipkins, national technical and product manager with Wormald New Zealand.
Tunnel fire protection is complex and each individual tunnel will have a different level of risk. This risk will be heavily influenced by factors such as the tunnel’s operational requirements, location, length, traffic conditions and the nature of vehicles that use it.
While the likelihood of a fire occurring in a tunnel is very small, the effects can be disastrous. To give an example, the Mont Blanc tunnel fire in France in 1999 occurred after a refrigerated trailer caught fire and stopped almost midway through the tunnel. The fire unfortunately resulted in many casualties and fatalities and the heat and smoke generated from the fire severely inhibited the emergency rescue operations.
It’s vital that every tunnel has an adequate fire safety solution in place. While it’s not always possible to provide an exhaustive checklist for tunnel fire safety, fire protection should always be considered in the initial stages of tunnel design. Consultation between tunnel operators, fire engineers and fire safety specialists will ensure that the final structure complies with recognised building requirements, engineering principles and applicable standards. It will also ensure that adequate safety features and emergency procedures are implemented.
When planning for fire protection, the number one priority will be the safety of tunnel occupants and emergency services personnel. Tunnel management will also want to make sure that damage to property is limited and the potential impact on operations is minimised.
Installing early warning fire detection systems will not only help to ensure that a fire is identified early in its development, but also monitor that development. Advanced detection solutions can provide prompt and accurate identification of a fire’s location. Many also readily accommodate the integration of closed circuit television (CCTV) cameras, a solution that is particularly suitable for long tunnels. These detection systems are designed to be directly connected to control centres, fire stations and emergency response units so that personnel are alerted in the event of a fire.
Detection systems are also designed to be integrated with fire suppression systems, which assist in controlling the growth of a fire. This can help tunnel occupants to safely evacuate and give fire-fighters the opportunity to get close to control and extinguish the fire.
Water deluge systems are a fire suppression solution commonly installed in tunnels. The systems are ideal for special hazard areas where fire can spread very quickly. Water deluge systems use open sprinklers or spray nozzles which are connected to a water supply through a deluge valve. A reliable and adequate source of water is vital so that an incident in any section of a tunnel does not deplete the supply of water. It is therefore essential that the water supply requirement be made a key consideration during the design stage of the tunnel.
The Wormald team recently installed water deluge systems as part of the fire protection upgrade works for the Mount Victoria Tunnel and Terrace Tunnel in Wellington.
In addition to fire detection and suppression systems, the safety of a tunnel may benefit from the fire protection equipment such as hydrants, hose reels and fire extinguishers. It is important that all fire protection equipment is strategically located within a tunnel and associated buildings so it is easily accessible to occupants, staff and emergency services personnel.
Tunnel fire protection is multifaceted. Careful and early planning is necessary to ensure that all risks are identified and the most appropriate solutions are provided. To ensure fire detection and protection systems and equipment are kept in proper working order, testing and maintenance should be carried out regularly. Maintenance schedules can be developed in consultation with a specialist fire protection company, with maintenance works typically happening at night to avoid disruption to tunnel traffic.