George Smith is a member of the tutor team at Outreachrescue based in the UK. He has twenty years experience working with emergency services from many different parts of the world. His specialisms are the delivery of work at height and rope rescue applications along with water rescue systems. He has also spent an unspecified number of years hanging from ropes, as evidenced by his long involvement with DMM over on the climbing side. In 2008 he co-directed the award winning film Upsidedown Wales.
When a cableway is tensioned between two anchorages and any kind of load placed on the system, relatively high forces are placed on the anchors compared to conventional rope rigging. The greater the tension applied to the cableway (ie. the wider the angle), the heftier the forces. There is a ‘magic angle’ of 120 degrees on the part of the cableway; here the force applied to the mid-point is equalled by that placed on the anchors; any wider angle of cableway will begin to create anchorage forces out of all proportion to the humble load exerted at its mid point.That’s not to say you can’t do it, but the moral of this story is that we must calculate the forces and create a suitably robust system – or if in doubt; over-engineer it! And, tension cableways as LITTLE as possible. (With a load-cell in controlled conditions the weight of 2 persons will tend to put about 3.5kN force on the anchors of a conventionally tensioned -1 person on a 3.1 pulley-cableway)
When we suddenly place a load on a system involving quite a lot of fabric it will stretch, which may be good from a comfort point of view but where do we end up? Stretch may be another good reason for the same over-engineering or pre-emptive elevation of the system. (E.g. use of high anchor points)
Cableway rigging is a game of two ends; any breakdown in the plan will result in an unseemly tug-of-war, soaking up considerable time. Visual aids like field guides, and multiple colours of rope are handy at the advanced end of the rigging spectrum.
The first rope has to be thrown, fired or hauled into place, and this may require a separate system involving initial use of a thinner line. At the cheap end of things, builders string might be considered, or bespoke shot bags, catapults crossbows and, (most fun), air propelled line guns.(Read the instructions and, ideally, attach the ‘line’…otherwise its just… a gun)
If you are trying to access a specific point, mid-span, it will need to be directly under the system, and this will dictate the selection of anchorage sites. Obvious? Not if you’re in a rush!
When those working on cableway systems experience difficulties, how easy is it for them to be accessed and rescued? And what are the possibilities of self rescue from something like a safe but inefficient system?
Now, here are some applications…
Simple Overhead Cableway to Protect People Working at Height
Basic safety rails and overhead ropes are commonplace in industrial rope working. A single judicially placed rope may suffice for some fall protection applications. If the system is beyond the reach of the operator they may connect to it via an extended attachment (such as a Grillion).
Occasional users may find it easy to establish these simple overhead systems using bespoke pre-threaded, cam-adjusted ropes (E.g. long Grillions) which can be rapidly established without the need for more elaborate cableway terminations.
If these systems are used for work positioning and rescue, clearly they will need to be doubled or trebled to suit potential rescue loads. (If using Grillions, check the diagrams in the user instructions. It is not permitted to tie them off mid-span, they don’t allow tensioning systems using rope-locks, and they limit the number of operators on the system.)
The higher the cable rope the greater the range of movement operators have below, however limits must be set to ensure the system really works.
This type of rigging has rescue applications in land-slips where areas of potential anchorage have been interrupted by expanses of loose material. (We introduced it to the Indonesian Civil Defence to deal with this problem.)
Basic Cableway to Convey a Rescue Load Across Uneven/Difficult Ground
A typical application for rescue teams operating in irregular mountain terrain or urban rubble piles; it could also be useful in other unstable material like snow, sand or wet ground. The packaged casualty is carefully handled by rescuers who, by use of the system, can avoid a normal carry with associated manual handling.
Clearly a very realistic estimation of the journey and the loadings placed on the system will dictate numbers of required ropes, however it is not uncommon to use just one rope so long as the casualty is continually handled and is never elevated unnecessarily. A back-rope assists in the control of any journey beyond the horizontal.
An Inclined Cableway to Deflect an Operative or Rescue Load
Any operative or rescue party engaged in descent by a lowering system or abseil may have their path altered by connection to a bolt-on cableway. Gone are the days of any single rope job here, even if the deflection is minor; it could still be enough to interact unfavourably with a glass window! In rope access these systems are useful for reaching places that do not have an anchor directly above. In rescue they are used to enable the rescue party to leapfrog hazards at the base of a structure or natural cliff. (Avoid terms such as ‘death slide’.)
Conventional Semi-Horizontal Cableway Used by Access Operatives and Rescuers
Most related textbooks will suggest use of a minimum of two fixed ropes for the cableway itself. Er… ‘minimum of’ means you can use more if you want, without being subject to ridicule; It will stretch less, it will be less vulnerable to wear points, it won’t take many seconds longer to set up, and it will, in the technical parlance…look better!
The system will need a central focus, either a very big pulley or a rigging plate with more than one large carabiner or mallion joining it to the cableway. (Avoid use of combinations of single or twin cheek pulley here as they will foul up, and over-reliance on them creates situations where the pulleys dictate rope numbers when it should be the other way round!)
A big pulley; usually a Kooteny Carriage, will ride over knots and pass merrily over crossed ropes.
Belayed ‘tag-lines’ or ‘push-me-pull-you’ ropes will be required, not just to convey the load but also to ensure safety at the initial lower and ultimate raise. If these stages are dramatic in the least, further ropes might be considered. Often the system will resemble a neat rope-bridge until loaded, at which point it can become an ugly edge-management performance.
A situation to avoid is one in which those clawing in the tag-line are not so much overcoming the mass/friction of the rescue load, as the tension created by slow operation of the opposite belay team!
Gorge Lower and Raise
A gorge is not strictly required; this system conveys rescuers across a cableway in the normal fashion, whereupon they can be lowered by paying out cable ropes so that the rescuer can access the casualties below. They are then retrieved by re-tensioning of the cableway.
What could possibly go wrong? Well…
- You could run out of cable rope or tag line.
- The cable rope could get tangled or damaged as it passes through new, possibly unseen or loose terrain.
- The rescuer may need to self-rescue.
- The loaded cables may be hard to lower in any conventional sense; it’s a big load to place on the belay devices.
With all vector forces, terrain and pulley skills considered; the load may be too hard to retrieve, and this will only become apparent when it is too late. (With a mid-point load being lifted the mechanical advantage multiplied by the number of operatives pulling, should not exceed twelve e.g. four people on a 3:1)
To be fair; with the right level of elevation and sufficiently humble aspirations in terms of reach, the system does work and is often used simply to lift a rescue load a couple of metres before conveying it to a place of safety.
‘Reeve’ Systems; to Access a Point Below a Fixed Cableway
For those with enough training time and more rope than you could shake a stick at, Reeve systems afford a high degree of efficiency without the unknowns and potential user errors of the previous system.
Though complex-looking their component parts may be constructed separately. Once the cable-ropes are in place and tensioned, they are not altered throughout the task.
The main pulley/rigging plate is positioned by belayed tag lines. From it, a second plate is suspended via the ‘reeve’; a loop of rope controlled from the anchorage. (This is backed up with a further rope)
Now, there are two types of ‘Reeve’ system; the ‘Norwegian’…(no this is not a Monty Python sketch)… and the generally handier ‘English’ one. The former has a reeve rope from central plate to anchorage belay, facilitating a loop. The latter has a reeve rope from one end of the cableway to the other, passing through the central point to form a loop. So long as you have enough rope for this purpose (i.e. one that reaches the moon and back) it is a more versatile system, as a rescuer may travel to and fro on any length of reeve loop. This enables them to commence the operation from any position below the cableway without having to depart from the anchor/belay station. Likewise the casualty may be delivered to any point within the plane without the need for a lift, saving time and effort.
Have I sold the whole business of cableway usage, its simplicity, its effortlessly safe execution?… I haven’t have I!