Rappelling with very thin lines?

[TLM]

After on accident here involving a fire and people jumping out, I came think would it be possible to get yourself down from a building on very thin lines. Something like paracord or the even thinner Spectra/Dyneema lines, what would you need and what would be the minimum safe load capability needed? Some of these materials are strong enough that something like 100' of line (or maybe even more) would not take an impractical amount of space.

Does anyone have experince or references?

TLM

 

[phantomspook]

Paracord would work but after using it, your best throwing that paracord away.

I have used three para cords kinda braded together to rappel down to retrieve some telemetry stuff at a remote location off a steep hillside.

Its not recommended but hey its better than nothing right?

 

[trout #2]

I think 8-9mm is about the thinnest you want to go for a personal escape line, at least according to info from some climbing rope manufacturers I've seen. You want to make sure you go with cord/rope from a climbing company (probably obvious, but had to say it) as it will be far superior to comparable size stuff that you can get anywhere else. I also remember seeing some specialized stuff made specifically for use as an escape line for firefighters that may have been a little thinner/lighter/and much more heat resistant. I'll try to find some of those links and post back.

 

[ACMarina]

Trout, Galls carries that sort of stuff. I don't know about using paracord or 5mm line, but I'd sure as heck try it before I jumped out of anything. .

 

[phatch]

Thin cord is terribly difficult to control speed with. It doesn't develop the friction that thicker stuff does in rappel devices. The thinnest I know people use is 8 mm static. Many of them also use a munter mule in addition to the device for additional friction and control in the rappel.

Phil

 

[Moine]

Forget it. As Phil mentioned it, with paracord you won't be able to break, so you might as well jump.

Best thing is learn to (de)climb, or get one of those batman winches

Cheers,

David

 

[Sidewinder]

Umm...No, I would never use paracord to repel. Here's a better idea that I think would meet your requirements:

http://www.tadgear.com/x-treme gear/climbing gear main/aog_microrap_rappelling_kit.htm

 

[beezaur]

Basic dynamics here to illustrate:

If you lower an object down onto a beam so it just touches but bears no weight, then let go so it rests on the beam, then the bean is exposed to twice the weight of an object. That is doing things very gently, and says nothing about an actual lurch.

Now, consider that ropes' breaking strengths are reduced by perhaps 50% when they are bent over small radii, like in a rappelling device or over a ledge.

So, jostling is bad, and small radii are bad. You need 4x your weight just to break even so far.

Now add UV/thermal degredation and normal wear. Double it again to 8x your weight (still breaking even).

But you don't want to break even -- or break anything else -- so use 16x the weight you will lower. This gives you about twice the strength that may actually be required: a safety factor of 2.

I would use something with a breaking strength of around 16 x 250 lbs = 4000 lbs for myself and a light pack. This can be webbing or small rope, but rope will give more friction, which is good.

That is an absolute minimum. Anything goes wrong and SNAPPO! Don't use paracord unless you really like wheelchairs.

As for a way down, I would forgo the rappeling device and do a Dulfersitz:

http://www.traditionalmountaineering.org/FAQ_Dulfersitz.htm

But it does kind of hurt, and you will want to practice at very, very low heights.

Scott

 

[MelancholyMutt]

I rappell quite a bit and you can go all the way down to a 5mm cord as long as the working load (15% of tensile strength) is more than your weight and equipment combined (specifically spectra type cords). However, consider the friction and abrasion of the cord going over the cliff or ledge, a tiny scrape may cause the cord to fail critically. Anything under a 8mm cord will require a Personal Escape descender which is smaller than a regular descender and specifically designed for thinner ropes.

However, anything under an 8mm personal escape rope is taking your life in your hands... rappelling with this equipment should be done only if certain death is guaranteed if you do not escape. Paracord should never be used for rappelling because tensile strength is 550lbs which means the working strength is only 82 lbs. Also, Paracord is not a static line. Dynamic rope is very very bad for rappelling as it will stretch and bounce and may snap after a few bounds.

Also consider if rappelling out of a burning building, that ropes are highly inflammable and will melt under relative low heat.

 

[TLM]

Okay... I was thinking in terms of an emergency device which would only be used once. 4 mm Dyneema rope has a breaking strength of more than a 1800 kilos, its modulus is quite high (half of steel) so it does not stretch easily but true it does melt and loose its strength at fairly low temperatures. Abrasion resistance is quite good.

(If the 15% factor is used on standard paracord, you get only 37 kg which is somewhat on the pygmy class. I propably could try that instead of jumping)

Because of the small diameter bending is not as big a problem as with bigger ropes, of course there is a limit.

The material is slippery if uncoated so a good friction device is needed. Some good sites you had, have to look into this.

Thanks
TLM

 

[MelancholyMutt]

I use this one in my emergency kit...

do a search on the SMC escape 8
remember, escape rope is 8mm. Although I have used 7mm with it, it is considered effective with only 8mm ropes.

Something like this...
The PMI PED

can be rigged for smaller rope, but needs to be pre-threaded through the device, and friction level researched and determined before use.

 

[MelancholyMutt]

Okay... I was thinking in terms of an emergency device which would only be used once. 4 mm Dyneema rope has a breaking strength of more than a 1800 kilos, its modulus is quite high (half of steel) so it does not stretch easily but true it does melt and loose its strength at fairly low temperatures. Abrasion resistance is quite good.

(If the 15% factor is used on standard paracord, you get only 37 kg which is somewhat on the pygmy class. I propably could try that instead of jumping)

Because of the small diameter bending is not as big a problem as with bigger ropes, of course there is a limit.

The material is slippery if uncoated so a good friction device is needed. Some good sites you had, have to look into this.

Thanks
TLM

Well, thin is a very bad trait for rappelling rope. You also do not want to use your rope very close to it's working limit as making a knot degrades the strength of your rope during use, as does bending it over an object. Tensile strength of a rope may be very good, but putting lateral pressure on it also reduces your working strength dramatically.

The bottom line is, as much research that has gone into determining an acceptable escape rope by the National Fire Prevention Association in the United States, they have determined that the smallest diameter rope acceptable for personal escape (and yes, it is only to be used once) is an 8mm Kermantile rope with one exception of a 7.5mm rope. Also remember, not all 8mm ropes are acceptable.

I also looked into escape ropes recently and found that Sterling makes an Aramid fiber rope that resists heat up to 500 degrees Farenheit and is rated at 4900 lbs tensile strength. It is not currently NFPA approved, but certification is pending.

 

[TLM]

MM

Your argument for the thicker ropes sounds good. You can only put so much 8mm rope to a certain volume though. Is it handling thats the problem with the thinner ropes, otherwise the stronger materials would be in use?

Aramids take heat well but their transverse strength is not very good Dyneema/Spectra is a lot better. Vectran is somewhere in between.
Knot strength in aramids is lousy but excellent in Dyneema. I guess it comes down to the way friction is generated.

TLM

 

[MelancholyMutt]

Well, the main problem with thinner ropes is controllability. Let's put the abrasion issue aside for a little bit. One cannot grip and control a descent with any rope smaller than an 8mm rope. The 7mm I used caused so much friction in my gloved hand that I had suffered rope burns. A thicker glove would have meant that I would have been unable to grip the rope.

As for knot strength, it's a matter of percentages. Stronger materials still suffer from the same precentage of strength degredation for each type knot. There are published numbers that tell how much strength one loses with each type of knot. There is no escaping that.

It is unfortunate that rope is bulky and heavy. However, 8mm rope is by far much lighter than 11mm which is the standard for sport and military rappelling.

 

[TLM]

As for knot strength, it's a matter of percentages. Stronger materials still suffer from the same precentage of strength degredation for each type knot. There are published numbers that tell how much strength one loses with each type of knot. There is no escaping that.

Not quite, for a simple knot Kevlar loses something like 80% of tensile strength, Dyneema more like 30%. It does vary with the type of knot though as you said. The type of rope also affects this as does its thickness. If you take one Kevlar fiber the loss on simple knot is 90%, on Dyneema about 10%, this is because Kevlar fiber splits easily and Dyneema can actually have some plastic deformation without splitting.

But if I understand you correctly if I have a good enough friction device a thinner rope could be used?

TLM

 

[Doc Ron]

For about 10 years I taught mountaineering at the University. As a part of the program we discussed thin emergency backup lines that could make the difference should you make that dramatic mistake of rapelling to the end of your line and find that you miscalculated. Why would that happen? because of the dynamic nature of climbing ropes like Kernmantles sometimes folks will drop a line and rappel even if the rope doesn't reach the bottom as they expect the line to stretch. I used to climb in Yosemite every summer and I saw a lot of accidents. Incidentally, one of the reasons the ropes did not stretch as expected as they were old ropes and had reached their "Elongation limits" from climbing and falls. Folks wre just too cheap to buy a new rope after a fall.

Anyway, We tested paracord both 5 strand and 7 strand and found that it will work but (as mentioned elsewhere) you'd better not bounce. as for a brake, the single biner wrap worked fine. 7 or 8 wraps gave you pinkie control of descent.

Heat is another factor. If you go far the biner will heat and can get hot enough to effect the line strength. Anyone who has rappelled know that the gear gains a lot of heat on descents particularily if they are fast. It is best to remove the brake from the line immediately after a rappel to avoid toasting the line. We used a lot of Goldline on student rappels as it s a bit more resistant to heat than kernmantle types.

anyway.... I keep 100 feet of paracord and a locking biner in my kit. Good enough for a couple of stories of descent. Maybe from one terrace to another.

In all... I wouldn't want to use it but it is better than jumping.

Ron

 

[TLM]

Thanks Mr. Headlum, I'll promise that if I ever have to do anything like that I'll be very carefull.

TLM

 

[jamesraykenney]

After on accident here involving a fire and people jumping out, I came think would it be possible to get yourself down from a building on very thin lines. Something like paracord or the even thinner Spectra/Dyneema lines, what would you need and what would be the minimum safe load capability needed? Some of these materials are strong enough that something like 100' of line (or maybe even more) would not take an impractical amount of space.

Does anyone have experince or references?

TLM

Here you go... http://www.neropes.com/maxim_climbing/micro_rappel.htm

5mm 5,000 lb 1.7 lb/100ft
3mm 3,500 lb 0.7 lb/100ft

Hmmm I would need 1 lb of the 3mm stuff and 2 lb of the 5mm stuff
PLUS 2lb 10oz for the rappel rig....
So about 3lb for the 3mm rig and 4 lb for the 5mm rig...I think I would go for the extra security of the 5mm, but I need to see how bulky the line is before deciding...This would be for emergency exit out of the 10th floor... 300 ft would make me feel a lot safer(it is a 20 story building) and you do not want to find that you have enough rope to reach the ground but not if you have to tie the rope to something on the other side of the room from the window...

 

[jamesraykenney]

Basic dynamics here to illustrate:

If you lower an object down onto a beam so it just touches but bears no weight, then let go so it rests on the beam, then the bean is exposed to twice the weight of an object. That is doing things very gently, and says nothing about an actual lurch.

Now, consider that ropes' breaking strengths are reduced by perhaps 50% when they are bent over small radii, like in a rappelling device or over a ledge.

So, jostling is bad, and small radii are bad. You need 4x your weight just to break even so far.

Now add UV/thermal degredation and normal wear. Double it again to 8x your weight (still breaking even).

But you don't want to break even -- or break anything else -- so use 16x the weight you will lower. This gives you about twice the strength that may actually be required: a safety factor of 2.

I would use something with a breaking strength of around 16 x 250 lbs = 4000 lbs for myself and a light pack. This can be webbing or small rope, but rope will give more friction, which is good.

That is an absolute minimum. Anything goes wrong and SNAPPO! Don't use paracord unless you really like wheelchairs.

As for a way down, I would forgo the rappeling device and do a Dulfersitz:

http://www.traditionalmountaineering.org/FAQ_Dulfersitz.htm

But it does kind of hurt, and you will want to practice at very, very low heights.

Scott

With paracord, it would not only hurt, it would HURT!

 

[shanshui75]

new england ropes (also maxim) makes "tech cord" which was originally designed for such purposes. i use 20' sections for cordelettes. holds knots well and not too stiff but very pricey.

here's the link: www.neropes.com/techdata/tech_cord.htm

k