Required operational systems for a typical road tunnel include ventilation, lighting, traffic control and monitoring, closed circuit television (CCTV), fire detection and suppression, drainage, communications and alarms. During normal traffic flow these systems must be fully operational and capable of providing the safest environment within the tunnel.
The ventilation system must maintain the levels of vehicle-emitted contaminants at predetermined safe levels. Normally this involves the use of monitoring systems to detect the levels of carbon monoxide (CO), oxides of nitrogen (NOx) and/or particulate matter to provide the necessary control signals to adjust the ventilation system airflow rate. Some tunnel ventilation systems are managed on a programmed basis using time to determine levels, based on historical operations data. However, they still rely on detectors to signal contaminant excursions above the preset alarm point.
For lighting, tunnel threshold and transition zone(s) levels are fixed so motorists can safely enter and traverse the tunnel, and are adjusted to the changing conditions during the day. A tunnel lighting control system, normally comprising of a measurement device, controller and switching system, helps reduce energy consumption and needless demand on the lighting system elements. The measurement device is the key element, there are currently two types available; illuminance meters and luminance meters. Luminance meters should be installed in all tunnels to read the equivalent veiling luminance of the tunnel approach.
Non-normal operations
When traffic stops, the monitoring system and CCTV come into play, detecting a change in traffic flow that can indicate a non-normal operating condition and thus a potential incident. Non-normal incidents usually fall into two categories, with or without a fire. For control system operation, the primary difference is the need to identify, verify and locate the incident longitudinally within the tunnel. This is particularly true in the case of a fire.
Operation of the ventilation system will depend on the type of incident. If stopped traffic is the primary problem the control detection system functions continually, keeping the tunnel clear of excessive contaminants. If there is a fire, the system will be the major element in controlling the movement of smoke and providing a tenable environment.
Emerging technology
One recent development is CCTV surveillance systems that detect fire automatically using digital image analysis, enabling the operator to respond quickly in conjunction with the monitored traffic flow. This technology is in an early stage of development and, although deployed in a few modest trial tunnel installations, has not yet been totally proven in the road tunnel environment.
Analytical methods
New analytical tools in the tunnel fire safety industry permit more detailed evaluation of the impact of an incident on the tunnel operation and environment. The use of computational fluid dynamics (CFD), developed in the aircraft industry, has permitted the simulation of the movement of heated gases and smoke from a fire in all areas of a tunnel. This capability coupled with the newly developed emergency egress software can effectively assess the impact of smoke and heated gases, resulting from a tunnel fire, on the evacuation path and determine whether it is tenable. These tools also allow a better determination of the level of risk and permit the development and design of more appropriate systems to mitigate the risk.
Training
Given the ability to design and install relatively sophisticated systems to identify, verify, locate and respond to any event, the training of those who operate the systems becomes extremely critical.
The owner of any road tunnel must adequately satisfy the PTE requirements of tunnel emergency response operations:
Plan: Develop an integrated emergency response plan involving all responding agencies both internal and external that are pertinent.
Train: Develop an integrated ongoing emergency response-training programme for all personnel and responding agencies, including regular retraining.
Exercise: Schedule full-scale emergency response exercises to include all responders, ideally every six months; but these should be mandatory each year.
Only by attending to the PTE of tunnel emergency response operations will the safety of tunnels improve. We now have the analytical and design capability to provide safe operation and control systems for tunnelling.
Operations in today’s road tunnels are highly dependent on monitoring and control systems, and on the skill of the operational personnel. Some of the effort currently required of the operator can be simplified as new technology emerges, the key ingredients still remain as the skill and knowledge of a properly trained operator.
