This article was earlier published in Atkins Building Design Journal.
The simple task of designing a safety screen for station workers in the service areas of eight underground stations in Central London becomes a complex exercise when you consider that trains are passing at close range, at high speed, at close intervals, and with high voltage cables at a close distance overhead. In this context, the process of arriving at a safe and functional design solution becomes a case study that provides inspiration for an innovative approach to complex challenges.
Crossrail
Crossrail is building a new railway for London and the South East, running from Reading and Heathrow in the west, through 42 kilometres of new tunnels beneath London to Shenfield and Abbey Wood in the east. The £17.6 billion project is currently Europe’s largest infrastructure project and is set to be completed in phases, the first of which is planned to open by late 2020. The new railway, officially named as the Elizabeth line, will carry an estimated 200 million passengers per year, increasing central London’s rail capacity by 10%. Integrating new and existing infrastructure, the project includes the construction of 10 new stations as well as the upgrading of 30 existing stations. Within central London there are eight new underground stations and two new above ground stations which are linked by a common identity created using standardised components.
The unified set of architectural components and products form part of a line-wide design concept completed in 2011 by a multi-disciplinary design group comprising engineers, architects and package leaders from SNC-Lavalin’s Atkins, architects from Grimshaw, product designers and wayfinding experts from Maynard, and lighting designers from GIA Equation. Architecturally, the line-wide design includes aspects of the ticket hall, escalator, concourse and platform environments and offers passengers an easy-to-navigate environment that is unique to the Elizabeth line. The consistent design language is strongest within the below ground spaces of the five new tunnelled stations at Bond Street, Tottenham Court Road, Farringdon, Liverpool Street and Whitechapel due to their similar functional requirements.
Brief
Since 2012 the group has been working in a partnership with Crossrail’s Chief Engineer’s Group to develop requirements and integrate these essential components of the Elizabeth line for a World class passenger environment, economies of scale in construction through standardisation, operational reliability, and low-cost maintenance over the 120-year design life. Approaching the final stages of the construction process, Crossrail’s Chief Engineer’s Group asked the linewide team to come up with a standardised component design that allows station staff to safely access the Back of House areas in the train tunnels at the platform ends of Canary Warf, Whitechapel, Liverpool Street, Farringdon, Tottenham Court Road, Bond Street and Paddington stations.
The train tunnels are managed by Transport for London’s Rail for London, and workers accessing these areas and should be sufficiently qualified. These are areas where 200-metre-long trains pass every 150 seconds at 100 milimetres distance from the platform edge. They still have a speed of 100 kilometres per hour when they enter the stations before they slow down to zero using the length of the platforms. There are 25kV high voltage cables swinging at less than three metres from the platform surface overhead, which makes for a hazardous environment to work in at any measure. The station staff employed by Transport for London (TfL) that were required to enter these areas are not normally qualified to do this, so a solution was needed that would ensure the safety of these workers.
Safety First
The safety-first principle was first introduced in London in 1916 by a charity that wanted to reduce the number of road accidents in the city and has now become part of the Construction, UK Design and Management (CDM) regulation, following European directive 92/57/EEC, which requires everyone working in construction to reduce health and safety risks for anyone that builds, uses and maintains a structure to an acceptable level. For Crossrail this meant reducing risk levels in design and construction and use to ‘As Low As Reasonably Practicable’ (ALARP) to meet the legal duties embodied in the Health and Safety at Work Act 1974 and following UK Health and Safety Executive (HSE) guidance ‘Policy and Guidance on Reducing Risks As Low As Reasonably Practicable in Design’.
Using a process originally meant to design oil rigs, we will be able to design for unprecedented scenarios to arrive at solutions that are not just safe and functional, but also sustainable.
As Crossrail designs and systems are without precedent for the owner and maintainer (TfL), the design team could only partially depend on existing guidance to determine best practice design solutions. To achieve ALARP risk levels the team therefore used a design development tool and assurance process in Crossrail Requirements, the Common Safety Method (CSM), based on methods used in the oil and mining sectors. It consisted of a series of workshops attended by key designers, technical experts and the client to determine the safest design option. These workshops exceed the typical CDM workshops in scope because they not only cover design and construction phases but include the full design life cycle up until decommissioning and demolition.
Optioneering
An initial series of HAZID (Hazard Identification) workshops were attended by up to twenty people at the time, including the Crossrail Head of Architecture, Chief Engineers and Contact Leads, fire and train engineers, station designers and contractors and subcontractors and representatives of London Underground and Transport for London that liaised with workers unions. During these workshops they reviewed several design options, from balustrades to full height screens, rigid as well as openable, in various configurations and made of various materials.
The options were assessed against potential hazards and threats affecting people, the environment, assets and reputation. These included day-to-day operational scenarios and emergency deboarding and evacuation for example, whilst also considering technical requirements such as train envelope clearance, tunnel smoke egress, dynamic cyclic loading and piston effect and earthing and bonding strategies. For every option and every scenario, the risk level was determined by rating probability/likelihood against impact/severity, and the scores were recorded in risk registers.
The option with the lowest score came out as the preferred option. Then a HAZOP (Hazard and Operability Study) workshop was organised to assess the risk to personnel and equipment of the preferred option during design, construction, operations, maintenance, replacement, decommissioning and demolition phases. The result was a modular system fit for several configurations; a 2.5-metre high powder-coated metal screen to prevent static electrical shock with a mesh aperture small enough to prevent fingers to go through. At face value a disappointing result perhaps, especially when considering the extensive design process, except that it gives the assurance that it creates an environment of optimum safety.
Conclusion
Designing for the highly hazardous environment of the train tunnels turned a relatively mundane task into a complex exercise, and the highly collaborative model that was used to come to the safest solution provides inspiration on how to deliver innovative solutions for complex challenges. This process does not have to be limited to rail projects alone. Think for example of the circular economy, where the collaborative process could be extended to include not only design, construction, operation and demolition, but also recycling. This way, using a process originally meant to design oil rigs, we will be able to design for unprecedented scenarios to arrive at solutions that are not just safe and functional, but also sustainable.