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Can a hot abseil descender melt slings or rope?

Posted: 25 Sep 2019, 11:38
by T2
We've all been down big, dry abseils and found our descender was extremely hot by the end (I have a scar on my left arm where I suffered a burn from my device following a free-hanging 100m drop -- so have definitely managed to get one past 100°C).

The obvious question is whether a descender can get so hot that it would melt other gear. This is particularly relevant when using slings or other items made from Dyneema, which has a lower melting point than conventional fibres such as nylon or polyester.

The team at Black Diamond have written a great post looking into this issue which covers some of the testing they did: ... pel-slings.

First off, they tested how hot it was possible to get a device (note that they were using belay devices, primarily variations of the ATC. These have a much lower mass and smaller surface area than most canyoning specific descenders). Their results, perhaps unsurprisingly, showed that heavier abseilers and those going faster got the device hotter. Doing a series of long drops one after another also got the device hotter. But they couldn't get it past about 135°C.

Next they tested how hot a device had to be to cut through a range of ropes and slings. Even the Dyneema -- despite officially having a low melting point -- didn't cut until hit with a 250°C descender, much hotter than they could get it by abseiling.

Their conclusions were that in real world settings they couldn't get the device to reach a temperature that was hot enough to cut slings or rope. They did confirm that the speed of the abseil, and the mass of the load (abseiler plus pack weight) drastically affected how hot the device got. They also provide some recommendations to reduce the risk. It's well worth having a read of their full testing, results, and conclusions.