If you’ve rappelled more than 40 feet before, you probably have noticed your rappel device heats up when you use it. On long, free rappels, in fact, your ATC, Pirana, or other device of choice easily becomes hot enough to burn you good. I tend to immediately throw my Pirana in the closest pool of water in such situations, because if I don’t, I invariably burn my thigh or arm a few moments later. Whether throwing a 174º Pirana into 50º water warps or changes it, I have no idea.
Anyhow, canyoneer James Kehoe took a big step past casual observation in attempting to answer the long-standing question: Just how hot does a rappel device get on a 450-foot rappel? James posted his test results on the Canyons Group, and I thought I’d post them here for general interest. Take home message: Your rappel device can get REALLY hot, especially on long, free rappels. Take precautions to avoid licking the device upon touchdown and keep small infants at least 10 feet away at all times.
Thanks to Mr. Kehoe for posting his study. To find his original post, go the Yahoo Canyons Group and look at the 10/4/2010 posts.
I’ve been curious about heat generated by friction on long drops for awhile now and I’ve been looking at methods to test the effects. By coincidence, I was invited on canyon trip with very long overhanging rap. I understand this is a timely topic, so I figured I would post the data I collected.
Here’s the executive summary:
Observed maximum temperature increase for the ATC on a 450 ft drop was 87 deg Fahrenheit (87F outside temp, ATC temp 174F).
The temperatures were measured on a 450 ft drop, single strand, using a new 8mm Canyon Pro DS rope. All temperatures were taken using an IR thermometer at the moment of touch down. Five different canyoneers ATCs were measured. All canyoneers used 2 biners through the ATC and a biner through the leg loop. All canyoneers applied a Z-rig before the last 100 ft with the exception of the highest temperature reading. In the last case the rope was found to be core shot near the top (a topic for another post) and the canyoneer opt’d for using only a leg loop to maintain a smooth (though faster) rappel. The rappel was in the shade with low humidity.
DT OT TD Notes
115 88 27 very slow
135 88 47
143 88 55 jerky
123 88 35
174 87 87 fast, smooth, core shot
DT: descender temp
OT: outside temp
TD: temp difference
Average temperature increase was 50 degrees F.
Couple of additional notes:
I was able measure my ATC temperature during the descent, changes in speed quickly resulted in change of ATC temperature. On a 220′ overhanging rap I was able to easily induce temperature swings between 115 and 125F.
Carabiners seem to retain heat much longer then ATCs, however I have no data to back up this observation.
I sent this data out for a mini peer review before posting it. My understanding is nylon and polyester ropes have a melting point about 450F. Some information Tom Jones sent stated the maximum usable temperature should be ~194F. No time duration was provided.
From the data, it seems unlikely ATC can generate enough heat to damage the rope when stopped if the melting point is used. Using the limit Tom provided on hot day (100+ F) it probably possible to reach the limit, but you’d have be going very fast.
1. Carabiner heat measurements
2. Different diameter rope influence
3. Better data on how long it takes a ATC / Biner to dissipate heat built up by friction.