Reference Accident: 2022/07/22 Gaopo Creek (Mountain Goat Canyon Section)
A solo canyoneer descended a 60-meter waterfall using the self-lowering method. As they progressed down the pitch, they discovered their rope was not long enough to reach to the base of the waterfall. They locked off and connected a second rope to their first rope via a double sheet bend. The canyoneer fell to the ground during the process of transferring load to the second rope. This study concludes the accident was the result of a failure of the double sheet bend.
Canyon Accident Reconstruction
Prior to running this exercise, we carried out basic fact-finding on the accident to serve as a reference for the situation in question. The equipment on the operator’s body is simulated to reflect the accident based on first-person GoPro footage recovered from the scene.
However, the content of this article is still conjecture based on our understanding and cannot be said to be a flawless reconstruction of the accident in question.
| Known Conditions | Waterfall height: 60 meters White Rope length: 70 meters Green Rope length: 38 meters After the fall, the white rope and the green rope have completely separated. The operator’s descender is locked and connected to the green rope and the operator. The hand ascender is connected to the white rope. |
| Unknown Conditions | We do not know whether the party knew the height of the waterfall in advance. |
Rope System Before the Fall
Figure 1:
At this time, after the operator used the white rope to lower himself, they found that the rope length was insufficient to reach the ground. First, they tie a VT Prusik in a prusik hitch around both ends of the white rope. Then, they proceed to join the green rope to both ends of the white rope with a double sheet bend. (Note: is a rarely used bend in the canyoning community in Taiwan.) After the ropes are connected, they transfer their descender to the green rope and lock it off.
Close-up of the Double Sheet Bend
Figure 2:
The operator disassembles the prusik hitch on the white rope before attempting to reinstall it on the green rope. Please pay attention to the shape of the double sheet bend below it before disassembly. It appears that one end of the white rope is unusually short. There is not enough tail length left to ensure the security of the double sheet bend. It appears to be almost hidden in the knot or flush. However, the rappeler’s weight is still on the prusik hitch. Consequently, there is no hint of the double sheet bend deforming or failing yet. (It is also possible that the movements of disassembling the prusik hitch additionally contributed to deforming of the double sheet bend)
Failure of Double Sheet Bend
Figure 3:
After the operator disassembles the prusik hitch, their load is transferred to the connecting knot via the descender on the green rope. At this point, due to insufficient rope tail which in turn causes the bend to deform, the double sheet bend releases. As the bend releases, the ropes separate, putting the rappeler into free fall. (Main reason: Sheet Bend knot released.)
Conclusions
Self-lowering Rappel Method Increases Risk
The self-lowering rappel method that contributed to this accident is usually reserved for setting traverse lines, handlines to known belay stations, or for scouting a drop before installing an anchor.
It is occasionally used for rappeling in specific situations. This includes when there is a direct line of sight to the bottom of a pitch, and when there is no danger from flowing water. It should not be used in risky environments or where its use will create a loss in team efficiency.
Rappeling A Pitch Using Self-Lowering Method
If self-lowering is being used to descend a complete pitch, the following conditions must be met:
- bottom of pitch is completely dry or still water
- the bottom of the pitch is in clear view
- pitch distance is less than half of the rope being used
Rescue-Related Concerns When Self-lowering
The self-lowering system is not releasable for rescuers at the anchor. Unlike other releasable rope systems, a rescue cannot be performed with the existing rope system. In the case of an issue with the system, unless the rappeler is able to rescue themself, additional equipment, additional time, and another rope is needed to perform a rescue.
The Security of Sheet Bends
Bends are a form of knot that may fail without adequate tail length. There is a risk of a bend loosening or deforming upon loading. There should be sufficient rope tail and an additional stopper knot tied after any bend.
Visit the Taiwan River Accident Database to browse more river tracing and canyoning accident reports.