Case Study: Track Transit for T5
Track Transit Tunnel Vent & Life Safety System
Heathrow Airport’s Terminal 5 building handles over 35 million passengers a year. It consists of a main terminal, T5A and two satellite terminal buildings, T5B and T5C.
The terminals are connected by two underground tunnels which house a Track Transit System (an Automated People Mover or commonly referred to as a train) that carries passengers to and from their flights in T5B and C to the main terminal.
AIS were involved from the early stages of the project – as consultants to Balfour Beatty – to develop the requirements specification. The system was designed with a formal safety rating – Safety Integrity Level (SIL) 2 – in accordance with ES EN 61508.
Working with Siemens, AIS tendered for and were engaged by Heathrow Airport’s contractors, over a two-phase development, to design and build the life safety system for the TTS. This covered tunnel ventilation and active signage for passenger self-rescue.
The provision of the system was a key part of the safety case for the railway which was developed and certified to rail standards, in accordance with Rail Regulation requirements.
“The Siemens and AIS team have demonstrated new standards for what we can and want to expect from our contractors – the quality of their work and their communications with the operational team was excellent, we are very pleased with the delivered safety system and the support they have provided us. “
Maintenance Manager, Track Transit System
Using Siemens SIL approved PLCs and standard HMI displays, AIS developed a distributed safety system that automates the operation of the ventilation system once the operator has selected the evacuation route to be used during a fire incident.
To provide the life safety functions, the system interfaces to:
- 12 axial fans (four fan stations each containing three fans) that provide supply or extract functions
- Secret signs – situated along the length of the tunnel and illuminated to point in the direction of the escape route – once the operator has selected the appropriate ventilation mode
- The Bombardier train controller –to determine the location of the train – via high reliability digital signals that relate to the zones the train occupies as it transits the tunnel.
AIS Added Value as Control System Integrators
- Involved as consultants during the early design stage of the contract – developed and delivered the requirements specification that was used as the basis of the tender
- Designed and delivered a system that was fully integrated with the railway and met the formal SIL2 safety requirements
- Involved as part of the overall safety team that worked on the integrated safety case for the railway – including submissions and presentations to the Independent and Competent Person (ICP) who was employed to ensure compliance with Rail Regulations.
In an emergency situation, the system is initiated by the railway operator, based on the location of trains and the fire. Therefore a significant investment was made in the design of the user interface, involving the operators throughout the prototyping process using a formal method called ‘Teach Back’.
This process involves questioning the operator on their requirements, prototyping the user interface based on these requirements and then ‘teaching back’ to the operator how the system should be operated. The technique is based on the principle that people are not very good at explaining fully what they want, but they are very good at spotting design flaws.
Using this method through an iterative process ensures that the final user interface developed fully meets the requirements of the operator – thus ensuring that the safety systems can be deployed quickly and effectively.
In addition to the standard emergency modes, the system is also programmed with back up modes. These come into effect if ventilation equipment is in fault and affecting the ability of the system to ventilate the TTS in accordance with the prescribed mode requested by the operator.
Back-up modes are deployed automatically by the system without the requirement for operator intervention. Once the operator selects the direction of ventilation – the system initiates the control of system and, if some of the equipment is faulty, this is automatically compensated for.