The roll call of railwaymen killed in the line of duty runs to depressing lengths. You don’t have to venture too deeply into the past – only a few decades – to find annual trackworker fatality rates measured by the dozen; go back to the 19th century and the yearly toll reaches well into three figures. William Page (Chatham), Thomas Robertson (Haymarket), Solomon Bridge (King’s Cross), Allen Sykes (Morley), George Beckett (Red Hill), Henry Brown and Thomas Jackson (Birkenhead) all lost their lives to trains in the first nine months of 1900. Yet these seven deaths actually represent a very narrow subset of the overall figure. We highlight them because of their common thread: the sites of work at the stated locations were all in tunnels.

Being healthy and safe at work is an absolute expectation for every one of us, no matter how adventurous we choose to be in our leisure time. It’s unfortunate that ‘health and safety’ has had its reputation tarnished by occasional overzealousness over recent years, but that should not detract from the bigger picture – in its purest 1974 form, hundreds of railway workers can thank it for keeping them alive.

Long consigned to history are the days of scuttling off to the nearest refuge when a change in air pressure tugged on the lookout’s ears, suggesting that a train had just passed through the portal. Nowadays, tunnel work is generally safeguarded: all lines blocked. Whilst the rules don’t preclude a halfway house – one line blocked but the other still open – many would assert that the applicable protection methods are not sufficiently robust. Certainly, the activities that can be productively pursued in such circumstances are quite limited.

Of course, none of this helps engineers to clear the contents of their job bank, a reality exacerbated by increasingly constrained track access availability, particularly on midweek nights, and time-consuming possession arrangements. Accordingly, resources are becoming stretched – driving up costs – as more and more activities end up shoehorned into comparatively generous blockages at the weekend, leaving too many workgroups twiddling their thumbs during the week.

It makes no sense and something will have to give if the railway is to deliver on its efficiency obligations.

Typical tunnel lining repairs, carried out with both lines blocked.

Half and half

Sincere words are often spoken about the industry’s willingness to embrace innovation and accrue the emerging benefits. New technology, better working practices and mechanical advancement are already freeing-up funds and enabling more work to be accomplished in less time. But there remains, in tunnels, an understandable reticence to do things differently. As our introduction shows, history is clear about the potential consequences of mixing men and trains. But what if that half-way house – working on one line whilst the other remains open – could be adopted with zero risk of harm to the workforce?

Long-time collaborators AMCO Rail and Foulstone Forge have been putting their collective minds to this. It’s the sort of thing they’ve been doing for years – developing bespoke solutions to tackle unusual challenges. And they’ve been hugely successful at it. This one though is unique: the concept, development and build phases have been relatively straightforward; it’s the high cultural barrier that’s most difficult to overcome.

In summary, what they’ve produced is a robust screen system which isolates the workforce from the tunnel environment, except for that part of the lining to be worked on. It provides access from the toe of the sidewall up to the high haunch and, being constructed as modular units, can be extended to cover any reasonable distance.

The intention is to facilitate the introduction of adjacent single line working without compromising the safety of the workgroup, thus allowing a limited service to be maintained throughout a major project – which might otherwise necessitate a full blockade – or create a less disruptive midweek-night regime for minor works on a route used overnight by freight traffic. Everybody wins.

Safety unfolds

Each unit comprises a steel base measuring 3.4 x 2.3 metres, designed so that a pair of units can be secured to a single T8 trailer using twist locks and hauled into position by an RRV. As such, they have to meet OTP requirements. So as not to affect the open line, on/off- tracking would be possible by means of a virtual siding and non-intrusive crossing system.

The screen protecting the work area – along one side of the base – is formed in three sections:

  • A primary fixed vertical panel, 2.4 metres in height;
  • A secondary overlapping vertical panel of 1.4 metres, supported at each end by two-metre telescopic columns which can raise it by 1.3 metres;
  • A folding panel, also of 1.4 metres, which travels horizontally to ensure the screen’s 1.72 metre loading gauge profile remains within that of a standard shipping container, but can be rotated to stand vertically (or any angle in-between) by means of hydraulic rams.

On the other side of the base is a two-part hinged skirt, stored in the vertical position but folded outwards into the cess when work is taking place. The skirt can be adapted to create a platform for activities at the haunch or covered with a geotextile to catch any rebound from spray concrete operations, allowing the material to be cleared away without the need to manhandle it.

Typically, deployment of one screen takes less than five minutes, with all parts controlled simply by four levers. There is a fail-safe system to ensure no part can pass beyond vertical towards the open line, whilst a winch is provided to hand-wind the various elements back into their travelling position in the event of a hydraulics failure.

As you would expect, LED lights illuminate both the working area and tunnel lining.

Fresh breath

The rush of air generated by a passing train has two components – a positive impulse of about 5kPa, followed shortly after by a 3kPa negative impulse. To reduce the effect of these pressure waves on the structure of the screen, all three panels are fitted with filters covering most of their cross-sectional area, allowing air to pass through with minimal resistance (68Pa/m2). On the working side, louvres direct the flow down towards the floor, ensuring little disturbance to the workforce.

When the screen is used as a standalone system, the filters serve the additional purpose of capturing any contaminants – cement dust, for example – that might otherwise be drawn back into the tunnel during the negative impulse. However, for activities such as spray concrete application, a ventilation unit and generator will accompany the screen – also carried on T8 trailers – capable of extracting 22,000-30,000m3 of air per hour at 4,000Pa by means of two 15kW fans.

Inside the unit are rows of polyester sacks – with a total surface area of 240m2 – to capture any particulates which then fall into a lower chamber when the sacks are shaken. From there, they are pumped into bags using an Archimedes screw. The air is discharged clean from the top of the unit and used to dilute the generator’s exhaust gases.

“In the working area, there’s a 600mm flexible hose and you place that where you need it,” explained Chris Scott of Foulstone Forge, who has designed and built both the screen and ventilation system. “This has the same effect as moving the extraction fan. The resulting air flow moves at about 0.35 metres per second which is enough to be effective without causing discomfort to those working in the area.”

Leap of faith

For longer-duration activities, there is potential to build additional units such as storage and welfare facilities or a workshop. This would elevate the screen concept to that of a factory train – bringing further efficiency benefits – although a broader range of approval requirements would have to be complied with in order to transport the screens as freight.

Dave Thomas, AMCO Rail’s contracts manager, believes the best approach is to “start small but think big. Minor works with one trailer and one screen: pointing, stitching, grouting, recasing, site investigations. Why not? Then, once people have got confidence in it – they see the savings, see the potential – we build more screens and use them for the majority of our tunnel works.”

The railway is, of course, justified in taking a cautious approach to change. But change there must be – the Rail Delivery Group made a statement to that effect in November. Operators’ success in attracting more people onto trains – and the implications of that in terms of introducing new services – places further strain on already limited possession opportunities, so engineers need to develop better means of fulfilling their obligations.

It’s easy to find reasons to maintain the status quo. However, AMCO Rail will be hoping to convince decision-makers that the case for change is more compelling when it hosts a demonstration of the tunnel screen on the Ecclesbourne Valley Railway at Duffield, Derbyshire on Friday 27 January. Why not come along and see how the future of tunnel working might look?

Written by Graeme Bickerdike


A limited number of places are available for the demonstration on a first-come first-served basis. Applications should be sent to: tunnel-screen-demo@amco.co.uk