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ABSEILING AND BELAYING ACCIDENTS WITH A FIGURE-OF-EIGHT

SUMMARY

An abseiling accident at an adventure centre is analysed in detail, and a belaying accident in less detail. In both cases the failure was due to the Figure-of-Eight levering the gate of a screwgate karabiner open, breaking the gate sleeve in the process. In both cases the Figure-of-Eight came free, with fatal consequences in the abseiling accident, and potentially fatal consequences in any such accident. There are important conclusions relevant to adventure centres, climbers, and manufacturers.

This failure mode must be rare, since it does not seem to have been recorded previously. Nevertheless, because of the potentially catastrophic consequences, the information needs to be well publicised.

1. INTRODUCTION

A student at an adventure centre was preparing for a high-speed abseil from a road bridge down to another road 40 metres below. Standard climbers' abseil kit was being used ie. a sit harness with a belay loop, and a Figure-of-Eight attached to the belay loop by a screwgate karabiner. The rope, which was an abseil rope (not a dynamic rope), was securely attached to the steel railing of the bridge.

Although the student had only learnt to abseil the day before, a safety rope was not being used. The adventure centre had found that a safety rope could not be paid out fast enough to allow high-speed abseiling, and hence such a rope was not used. However, an instructor was on the road below, holding the bottom end of the abseil rope, so that he could apply a braking force, in case the student lost control during the abseil.

The student stood with his feet on the parapet of the bridge, and started to lower himself into the abseil. When he looked down, he was understandably nervous, and pulled himself back into a standing position. He had another go, but again pulled himself back. Eventually he committed himself and launched himself into the abseil. Almost immediately he became detached from the rope and went into free fall. He landed on the road below, suffering multiple injuries from which he died.

The Figure-of-Eight remained attached to the rope near the top. The screwgate karabiner was found attached to the belay loop of his harness, with the gate open. The screw sleeve on the gate was fully screwed up, but with a notch broken out of it. The gate could not be closed without first unscrewing the sleeve almost two complete turns. The karabiner then worked as normal.

The Devon and Cornwall Constabulary sought the opinion of the BMC in answer to the questions:

*   How did the Figure-of-Eight become separated from the karabiner?

*   Was the equipment faulty?

As a consequence, an investigation was carried out by a BMC-recommended expert, and his report (reference 1) formed part of the proceedings of the coroner's inquest into the student's death.

This present BMC report summarizes the findings of reference 1, and also briefly discusses a potentially lethal accident in which a combination of a Figure-of-Eight and a screwgate karabiner was being used for belaying.

2. EXAMINATION

In the abseiling accident the equipment being used was of the type used regularly by climbers and mountaineers for this purpose. The Figure-of-Eight, although worn, was adequately strong for its purpose. The karabiner was in new condition, apart from the notch in the gate sleeve.

The damage to the gate sleeve was very similar to that seen in another recent Technical Committee investigation (reference 2), and that suggested a likely explanation of events, as described below.

3. TESTING AND ANALYSIS

The student was using the gear in the configuration shown in Fig. 1. He had been taught the previous day to hold the free end of the rope well-back and close to his body. However, he pulled himself forward into an upright position on three or four occasions, allowing the karabiner and Figure-of-Eight to become slack each time (Fig. 2).

When the gear is loaded again, there is a tendency for the Figure-of-Eight to turn over, and take up an abnormal configuration in relation to the karabiner, particularly in relation to the karabiner gate. In this position, the Figure-of-Eight can both load the karabiner axially and apply leverage to the gate. This abnormal configuration was noticed and corrected by the abseiling instructor on each occasion except the last. In a test laboratory, using a karabiner with the gate unscrewed, it can be shown that when the load is re-applied, the abnormal configuration does not necessarily straighten itself out, and the Figure-of-Eight can lever the gate open and escape (see Figs. 3, 4, and 5, taken from reference 1).

This abnormal configuration of Figure-of-Eight and karabiner is very close to instability, ie. to straightening itself out when loaded. However, a stable configuration could be found. Using a new karabiner of the same model, this configuration was tested in a tensile test machine. (Since the configuration cannot safely be held in the correct orientation by hand whilst the machine takes up the load, a piece of masking tape was used to do this, but it was not considered to have affected the results.) Three tests were carried out in the tensile test machine. The peak failure forces were:

Test 1 - 0.77 kN
Test 2 - 1.04 kN
Test 3 - 1.03 kN

The damage to the sleeve of each test karabiner was virtually identical, and virtually indistinguishable from the karabiner damaged in the accident.

The student was fairly heavy, weighing 98 kg. His gravitational force would be 0.96 kN, so any small jump or shock loading would have been enough to break the Figure-of-Eight out of the karabiner.

Later Test Work

The author of this report weighs 70 kg, and hence has a gravitational force of 0.69 kN. Given the above failure forces, he should be able to apply his body weight, without shock, to the abnormal configuration of karabiner and Figure-of-Eight without it breaking. However, applying the load suddenly should generate a peak force at least twice his gravitational force, and hence be enough to break the Figure-of-Eight out of the karabiner. Using a combination of slings, and another new karabiner with the Figure-of-Eight in the abnormal configuration, all hanging from his garage ceiling, the author was able to step very gently into a sling and hang there without breaking the karabiner or straightening the gear out. The author then stood on the sling suddenly; the karabiner gate sleeve broke, and the Figure-of-Eight popped out of the karabiner. The damage to the gate sleeve was again virtually identical to the other test results and to the karabiner in the accident.

This test result is consistent with the results of the tensile testing, and further demonstrates the practicality of the explanation of how the accident happened.

4. DISCUSSION The following technical conclusions are taken from reference 1, with minor changes for consistency.

*   There were no indications that the broken karabiner was in any way defective or deficient, compared with other karabiners of the same model, or compared with other karabiners of similar type.

*   There were no indications of any defects or deficiencies in any of the other equipment, which were material to the cause or consequences of the accident.

*   A hypothesis has been put forward covering the sequence of events in the accident, as follows. Starting with the configuration shown in Fig 1, the student pulled himself forward, prior to abseiling, allowing the abseil gear to become slack, Fig 2, though he kept the rope tight. When he moved back to commence the abseil, the Figure-of-Eight and karabiner were in an abnormal configuration when they began to take the load. At this time he may also have grabbed hold of them with his left hand, Fig 3, and effectively held them in this configuration. As he transferred his weight to the gear, with a bit of a jump, the force rapidly built up to a level at which the Figure-of-Eight levered the karabiner gate open, Fig 4, and itself became detached from the karabiner, Fig 5. His only connection with the system would then be his right hand on the abseil rope. He was in free fall.

*   Laboratory tests have shown that the force required to break the Figure-of-Eight out of the karabiner in the abnormal configuration is only marginally in excess of the student's gravitational force (his weight). A small jerk or jump would be more than adequate to cause breakage of the karabiner, in this configuration.

*   The observed damage to the karabiners in the tests was virtually identical to that observed on the karabiner involved in the accident.

*   Although the hypothesis can never be proven, the analysis and test work are all consistent with the hypothesis. This hypothesis is considered to be the most likely explanation of the events.

The later test work by the author is consistent with the above conclusions.

Implications for Adventure Centres

It does not seem to be generally appreciated that climbing gear is not primarily designed to be safe. Its design is a compromise between the demands of safety, low weight, and speed of use. A climber, who has to carry his gear up and down a climb, clearly wants low weight, also speed of use can increase safety in many climbing situations. To achieve these factors, climbers are prepared to compromise on safety and accept minimal margins on strength. The risk is accepted as part of the activity. The strengths marked on climbing gear are failure strengths ie the gear may break at these loads. Compare this with industrial engineering where, for example, lifting gear will be marked only with a Safe Working Load (SWL). The failure load will be at least three times, in many cases five times, the SWL. This provides the safety margin against the unknown and unexpected. In climbing gear there are no safety margins. This is alright so long as it is understood.

Adventure centres which advertise abseiling and other so-called adventure activities, should re-assess all their gear and ask themselves whether they really need the low weight and speed of use of climbing gear, and whether there are not other alternatives which give higher safety margins against misuse and the unexpected, and which are inherently more reliable.

Applying the above general point to this specific accident, consider the karabiner in particular. Climbing karabiners are inherently weak, and are prone to misuse. They are designed to be light and to be easily opened, and hence can easily come open when not required. Manually locking gates (screwgates) and auto-locking gates are designed to stop the gate being opened inadvertently. They are not designed to stop the gate being levered open, or otherwise forced open.

Taking everything into account, karabiners do not have a high reliability as a closure. Much higher reliability can be achieved with a screwed-closure connector (to EN 12275) eg a "Maillon Rapide," which needs a tool to fasten it up and undo it. Cavers, who do a lot more abseiling than climbers do, use a Maillon Rapide as the standard means of attachment of their abseiling gear to their harness. They do this because it is more reliable than a karabiner, and is better able to withstand three-way loading.

Implications for Climbers

As mentioned above, climbers require low weight and would be reluctant to use a heavy connector. At present there are no strength requirements specified for karabiner gate sleeves in the Connector Standard. They are purely to prevent the gate being opened inadvertently. It is unlikely that twistlock sleeves are significantly stronger than screwgate sleeves. It would seem desirable for manufacturers to produce karabiners with stronger gate-locking devices, for use with a Figure-of-Eight.

In the meantime, an alternative approach, for the individual climber, would be not to connect a karabiner directly to a Figure-of-Eight. If a short tape sling were passed through the small end of the Figure-of-Eight and then clipped into the karabiner, the Figure-of-Eight would be unable to exert any leverage on the karabiner gate, and the problem would be avoided.

In the absence of any of the above solutions, climbers should take great care to ensure that the Figure-of-Eight and karabiner are always in the correct configuration, and always under load, especially when going over an edge or round a bulge. Jumping over an edge should be avoided. The penalty for getting it wrong is dire.

However, for climbers the problem is not restricted to abseiling; there is the same potential for accident when belaying.

Belaying Accident in Germany

Since the abseiling accident occurred at the adventure centre, a similar accident has occurred in Germany, but in this case whilst belaying (reference 3). A climber was being belayed using a Figure-of-Eight and a screwgate karabiner in a similar configuration to that used for abseiling. The belayer perhaps was not paying too much attention and allowed the gear to take up an abnormal configuration. The climber fell off, the rope came tight, the Figure-of-Eight levered the gate of the karabiner open, released itself, and the climber was then in free fall. It was only a matter of luck that the climber did not fall very far, and escaped serious or fatal injuries.

The damage to the karabiner gate sleeve was reported (reference 3) as identical to that in the abseiling accident and in the test results.

5. CONCLUSIONS

During abseiling, if the Figure-of-Eight and the karabiner to which it is attached become slack, they can take up an abnormal configuration, such that, when loaded, the Figure-of-Eight will lever the karabiner gate open and release itself, with potentially fatal consequences.

Adventure centres which advertise abseiling and other so-called adventure activities, should re-assess all their gear and ask themselves whether they really need the low weight and speed of use of climbing gear, and whether there are not other alternatives which give higher safety margins against misuse and the unexpected, and which are inherently more reliable.

If high-speed abseiling is to be offered as an adventure activity to novices, then, a more reliable means of connection than a karabiner should be used, such as a suitable size and strength of screwed-closure connector (eg a "Maillon Rapide").

For climbers, it would seem desirable for manufacturers to produce karabiners with stronger gate-locking devices, for use with a Figure-of-Eight.

An alternative approach, for an individual climber, would be not to connect a karabiner directly to a Figure-of-Eight. If a short tape sling were passed through the small end of the Figure-of-Eight and then clipped into the karabiner, the Figure-of-Eight would be unable to exert any leverage on the karabiner gate, and the problem would be avoided.

In the absence of any of the above solutions, climbers should take great care to ensure that the Figure-of-Eight and karabiner are always in the correct configuration, and always under load, especially when going over an edge or round a bulge. Jumping over an edge should be avoided. The penalty for getting it wrong is dire.

The same failure mode, with equally dire consequences, can occur when a climber is being belayed using a Figure-of-Eight, a common technique in sport climbing, and sometimes used in winter climbing. The belayer needs to take great care that the Figure-of-Eight and karabiner will not take up an abnormal configuration if the climber falls off. In the event of an accident, the consequences will occur to the climber, and not to the perpetrator of the accident, the belayer. This should be a salutary warning for sport climbers.

6. RECOMMENDATIONS

Because of the potentially fatal consequences of the failure mode involved, high publicity should be given to these accidents and the conclusions in this report, in the climbing press, and with adventure centres.

References

1. Abseil Accident at Tolskithy, Redruth, on 3 July 1996
Report of an Independent Technical Investigation
R N H McMillan 19 September 1996
NMR/961

2. BMC Technical Committee Memorandum TCM 95/11
Report for Incident 94/7/C.STA
Faders HMS Karabiner 6 June 1995
Alan Huyton

3. Pit Schubert, Deutsche Alpenverein
Private communication 1997

Author: Neville McMillan