Using slings for belaying during alpine multi-pitch tours
For alpine multi-pitch tours on rock, ice and mixed terrain, the belay spot is of central importance. It is therefore essential that the belay construction can withstand all conceivable impacts.
The important thing about belaying is to ensure that there is redundancy, in other words that the belay construction relies on several independent fixed points.
This can be achieved through various belaying techniques. Whereas anchor equalization (or triangle of forces) used to be considered the most practical solution for belaying, today series constructions are preferred. Both techniques rely on at least two independent fixed points. In the case of anchor equalization, a force triangle distributes the force over the two fixed points. In the case of a series construction, one fixed point is subject to the entire force, the second fixed point is only there for redundancy. Series constructions are therefore generally preferred if at least one strong fixed point (fixed anchors, bolt hangers) is available. If, however, the two fixed points are considered inadequate (pitons, nuts or other mobile securing devices), anchor equalization is the preferred technique.
Series constructions are based on the centre point principle:
In the lower of the two fixed points a locking carabiner is engaged. Subsequently, a double overhand knot is tied into a sufficiently long webbing sling so that there is a small hole in the loop. This centre loop (1) is then hooked over the locking carabiner. The loop itself is fixed to the second, upper fixed point (2) with the help of an additional carabiner a clove hitch tied into the double strand. To secure the knot, the end of the sling that remains after tying the clove hitch is connected to the carabiner (3) attached to the fixed point.
With the help of two HMS carabiners, the centre loop can now be used for belay construction, either for oneself or for one's partner.The connection made with the webbing sling between the two fixed points can be of fundamental importance, in particular if one of the fixed points fails and the force is transferred to the second fixed point. In addition to the redundant fixed point itself, it is also the connection between the two fixed points that is of fundamental importance. In order to prevent a rope team from falling, the webbing sling must be able to withstand all conceivable forces that may arise if one of the fixed points fails.
Effects of differences in materials when in practical use
Using slings for belaying
Polyamide slings can absorb up to 4% of their own weight in water. This has a reducing effect on the strength of the slings: wet polyamide can lose up to 25% of its strength. This is particularly important to consider if the surrounding of one's belay spot is wet. Be careful using permanently fixed slings. These "overwinter" at the belay spot and are thus subject to wetness over a long period. Always thoroughly check the slings you come across at your belay spot. If in doubt, use your own, undamaged sling to create redundancy.
Knots in a sling mean that the webbing material is subject to smaller deflection radii. This reduces the strength of the sling. Knots in slings (tied into the double strand) reduce the breaking strength by an average of approx. 45%. Knots in webbing slings should therefore be avoided as far as possible. If you cannot do without a knot in your sling when climbing/mountain climbing, you should use knots that have the least effect on the strength of the sling. Your choice should be polyamide slings, as these are less weakened by knots.
The lower melting point of Dyneema® has no adverse effects. Even if your belay technique is based on a series construction and you create a centre loop by tying a double overhand knot, the friction caused by the moving knot when under load will not result in the sling burning through. There is only a risk of the sling burning through if the frictional heat is generated on a stationary sling. It is therefore important never to pull the rope through the sling. When abseiling or belaying, it is therefore important to ensure that there is no friction between the rope and the slings.
Elongation at break
Dyneema® is a very static material. Dyneema® slings are therefore not suitable for belaying if your technique is based on a series construction. The strength-reducing effect of the clove hitch tied into the single strand is too great. Dyneema® slings must therefore only be used with double strands.
The UV resistance of slings can hardly be measured. The UV resistance of webbing slings only plays a role if you come across permanently fixed slings at your belay spot. These slings are exposed to sunlight for prolonged periods. Again, permanently fixed webbing material should be critically examined and ideally be replaced with your own, undamaged sling.
Material recommendation for belaying
Despite these factors, the use of webbing slings is generally considered safe. The prerequisite is of course that only undamaged webbing material is used for belaying and that it is used properly. Situations only become dangerous if several strength-reducing factors occur at the same time. It is therefore important to continuously check the slings and keep track of their histories.
Base your decision whether the sling or webbing needs to be replaced on the following points:
- After a hard fall (mechanical damage as the result of frictional heat)If the seam pattern is damaged (doubts in relation to strength)
- In the event of irreversibly heavy soiling (for example, by grease, bitumen, oil, etc.)
- After contact with acids, for instance from a car battery
- After high thermal exposure (visible melting or signs of melting)
- If after such an incident you are in any doubt regarding the strength of the sling, you must replace it under all circumstances.
When using webbing slings for belaying, the following summarising points must be observed:
- Only use undamaged webbing slings that have a known history (age, number of climbing tours, number of falls etc.).
- If several strength-reducing factors occur at the same time, the strength reduction of the sling can become critical.
- Tying knots into slings during belaying should be avoided as far as possible (if you need to extend a sling, you can also do this with a carabiner)
- Slings must never lie on top of each other
- It is important to ensure that no rope is in frictional contact with the sling as this can cause the sling to burn through
- If slings have to be knotted, always tie the knot into both strands of the slingIf your belaying technique is based on a series construction, polyamide slings are the preferred choice since they are less weakened by the knots
- Due to the considerable reduction in strength caused by knots,
- Dyneema® slings are less suitable for belaying purposes