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consequence of fast rappel on rope ?


Original Post
curvenut · · Unknown Hometown · Joined Jul 2007 · Points: 0

Hi MP ,

     What are the effect bad or good on a rope when you rappel fast ?

I known that the heat generate  make the rappel device very hot. 

1 - Does fast rappel wear more the rope ?

2 - Does the heat generated during the fast rappel burn the rope ?

3 - When on the ground,  the time we remove the device, is it long enough to burn and affect the strength of the rope ?

Cheers, 

EDIT :     I am not rappelling fast,  I am just wondering ! ;-)

eli poss · · Durango, Co · Joined May 2014 · Points: 456

no, it doesn't get anywhere near hot enough to damage the rope. It doesn't even get hot enough to melt dyneema. I don't know whether it wears more on the rope but I would imagine that it would certainly put more wear on carabiners used to rap, especially if you are using a megajul/alpine smart type device to rap.

John Wilder · · Las Vegas, NV · Joined Feb 2004 · Points: 1,530

You can melt the top layer of a rope if you rappel or lower too quickly with a grigri. It's not super bad for the rope, but it certainly shortens its life span. 

ViperScale · · Unknown Hometown · Joined Dec 2013 · Points: 235
John Wilder wrote:

You can melt the top layer of a rope if you rappel or lower too quickly with a grigri. It's not super bad for the rope, but it certainly shortens its life span. 

I don't know who told you this but I am pretty sure the grigri thing is a myth. There is a video where they tested this out by pulling a belay device through a rope with a car, far faster than you are going to physically rappel and they never could do any damage to it. If a normal belay device can only get up to like 135 °C in a real world rappel going fast I find it hard to believe a grigri can get up another 85 °C and hot enough to melt it.

This is about slings and not the rope itself but here is some good information http://blackdiamondequipment.com/en_US/qc-lab-can-a-hot-belay-device-melt-my-rappel-slings.html.

Summary is they could not get a belay device over 135 °C (275 °F) in the real world. Nylon melts to liquid at around 460 °F, nylon will start or "move" or ooze at around 420 °F. Your rope is not going to be hurt by rappelling.

Jim Titt · · Germany · Joined Nov 2009 · Points: 490
ViperScale wrote:

I don't know who told you this but I am pretty sure the grigri thing is a myth. There is a video where they tested this out by pulling a belay device through a rope with a car, far faster than you are going to physically rappel and they never could do any damage to it. If a normal belay device can only get up to like 135 °C in a real world rappel going fast I find it hard to believe a grigri can get up another 85 °C and hot enough to melt it.

This is about slings and not the rope itself but here is some good information http://blackdiamondequipment.com/en_US/qc-lab-can-a-hot-belay-device-melt-my-rappel-slings.html.

Summary is they could not get a belay device over 135 °C (275 °F) in the real world. Nylon melts to liquid at around 460 °F, nylon will start or "move" or ooze at around 420 °F. Your rope is not going to be hurt by rappelling.

There is confusion about "melting" and glazing on nylon, it´s certainly easy enough to glaze the top layer of a rope, I see it all the time when testing belay devices. It is the combination of pressure and temperature which is the problem with devices like the GriGri which apply a relatively high pressure on a small area or rope and an extremely well studied phenomenon in engineering where nylon is used as a bearing material which is why the more expensive nylon bushes are filled with other materials. There are tables of the allowable pressures and temperatures available from any good bearing manufacturer or in engineering handbooks.

The glass transition point (which is the technical name for the effect) is much lower than the melting point, for nylon 6-6 around 70°C. The effect is most familiar to those who iron their clothes where the polymer chains are heated and aligned by the weight of the iron.

We did a research project on heating in belay devices when abseiling and there are several things to note; it is extremely difficult to accurately measure the temperature at the point of contact which in some devices is very small without embedding thermocouples in the device itself. The stainless steel parts in the GriGri, Cinch etc increase the problem as the rate of conduction away from the contact point is very low causing the main body to be relatively cool but at the actual contact point to be much higher which is even harder to measure. Just measuring the temperature of the entire device is worthless. 

Stainless steel belay devices have another problem as the specific heat capacity is approximately one half that of aluminium so for an equal mass the stainless plate heats up twice as fast.

In normal climbing applications there are no real difficulties but start abseiling a long distance or with more weight and problems start to occur.

Abseiling faster gives less time for the heat produced by friction to dissipate through the device and radiate into the surroundings and thus the device will heat up more.

Daniel James · · Chicago · Joined Aug 2016 · Points: 95

Glazing is definitely possible on rapid rappels.  There is a reason cavers tend to use rappel racks for big pitches, they are hard to beat for heat disipation.  I do remember being warned many a time to not rappel too quickly in caving contexts, and if I did then at the bottom not letting the hot rappel device stay in one spot lest the rope get glazed.  I had definitely seen older ropes that in their abuse had gotten glazed a bit.  It should be noted that this is all based on a caving context, where I'd be using a Petzl Stop or Simple, so I can't speak to the ATC's specific risk, but the concept is generally there.

BrianWS · · Unknown Hometown · Joined Apr 2010 · Points: 790

I've had a small section of rope glazed after a partner rapped with an ATC. Didn't seem to affect longevity of the rope.

ViperScale · · Unknown Hometown · Joined Dec 2013 · Points: 235

So does anyone have any studies / test done about glazing and the affect it has on the rope? Does it weaken the sheath? When the rope is glazed does it have any affect on the core?

Besides making the rope a little slick in the area where it glazed does it matter?

We all know the sheath is just there to protect the core you technically could cut the sheath off and still take a ton of overhanging route falls perfectly fine.

Derrick Keene · · Kentucky · Joined Apr 2017 · Points: 95

Glazed doughnuts are nice

Healyje · · PDX · Joined Jan 2006 · Points: 290

Can't think of a single good reason to be rappelling fast enough to do anything to a rope. Better idea - slow down.

DrRockso · · Red River Gorge, KY · Joined Sep 2013 · Points: 336
ViperScale wrote:

I don't know who told you this but I am pretty sure the grigri thing is a myth. There is a video where they tested this out by pulling a belay device through a rope with a car, far faster than you are going to physically rappel and they never could do any damage to it. If a normal belay device can only get up to like 135 °C in a real world rappel going fast I find it hard to believe a grigri can get up another 85 °C and hot enough to melt it.

This is about slings and not the rope itself but here is some good information http://blackdiamondequipment.com/en_US/qc-lab-can-a-hot-belay-device-melt-my-rappel-slings.html.

Summary is they could not get a belay device over 135 °C (275 °F) in the real world. Nylon melts to liquid at around 460 °F, nylon will start or "move" or ooze at around 420 °F. Your rope is not going to be hurt by rappelling.

Personal experience,  you can definitely glaze a sheath with a grI gri. In as little as 20 feet as a matter of fact. 

curvenut · · Unknown Hometown · Joined Jul 2007 · Points: 0

I may contact a couple rope manufacturers to have they opinion !

John Wilder · · Las Vegas, NV · Joined Feb 2004 · Points: 1,530

I was referring to glazing in my comment. Sorry it was late and my brain wasn't firing on all cylinders. 

Muscrat · · Unknown Hometown · Joined Oct 2011 · Points: 3,610

Did anyone mention you get to the bottom faster?

Brian in SLC · · Sandy, Utah · Joined Oct 2003 · Points: 13,772

I glazed the heck out of a..ahem...polypro rope on a long rappel.  Cured me of thinking that was a viable option for a tag/rappel line.  

highaltitudeflatulentexpulsion · · Colorado · Joined Oct 2012 · Points: 35

There are documented cases of people melting their rope and dying. These are always the super long rappel weirdos (2000' or more), going too fast, and probably using a brake bar. 

For rappelling off a climb you finished, there isn't enough length to get that hot. You probably don't have gloves, so you should keep your speed in check anyway. 

There is no advantage to a super fast rap.

Jim Titt · · Germany · Joined Nov 2009 · Points: 490
ViperScale wrote:

So does anyone have any studies / test done about glazing and the affect it has on the rope? Does it weaken the sheath? When the rope is glazed does it have any affect on the core?

Besides making the rope a little slick in the area where it glazed does it matter?

We all know the sheath is just there to protect the core you technically could cut the sheath off and still take a ton of overhanging route falls perfectly fine.

I can remember reading a paper on glazing of ropes and that it made no effect but where it was I´ve no idea, as you say the sheath is really only there to protect the core. The glazed part seems to dissapear quick enough anyway.

Edit:- it this paper  

And the bottom line was the strength was more or less unnaffected but the strands became stretchier (probably because the heat had affected the heat-crimp in the rope), they actually took the rope apart and measured the differences between the inner strands nearer and farther from the heat source.

David Coley · · UK · Joined Oct 2013 · Points: 70

I've glazed a rope on a hot day with a grigri even though I was going more slowly than I would with a belay plate.

Guideline #1: Don't be a jerk.

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