Biner Block concerns

[bigtoeski]

I have some concerns about the biner block method of rapelling.

1. If the biner falls onto rock below while pulling it down wouldn't it have a chance of creating hairline fractures inside the biner and then not be safe to trust?

2. It seems bulky, have people used the UIAA approved method of using the overhand knot to join 2 ropes, opinions on that?

Pros of using the biner block method would be you can save on having to use another heavy rope as the pull line. The overhand knot would only allow you to use 2 heavy same diameter ropes to be able to use it. Please post any comments! Thanks!

[charlybldr]

"1. If the biner falls onto rock below while pulling it down wouldn't it have a chance of creating hairline fractures inside the biner and then not be safe to trust?"

A. Yes, if the 'biner actually fell to the ground. Using a 'biner block does not put the carabiner in danger of falling. If you've set your rope length to the drop, the 'biner used in your block is half way between you, and the end of the rope. By the time the end of the rope cuts loose from the anchor above, the 'biner is in your hand.

"2. It seems bulky, have people used the UIAA approved method of using the overhand knot to join 2 ropes, opinions on that?"

A. Not any bulkier than a knot block (figure 8). These techniques offer two different shapes which can be used in different situations. Alternatives to the block should be considred if there is danger of jamming.

To join ropes I use the overhand with a long tail almost exclusively now. One nice thing is that this method tends to keep the knot out of the way during the pull.

"Pros of using the biner block method would be you can save on having to use another heavy rope as the pull line. The overhand knot would only allow you to use 2 heavy same diameter ropes to be able to use it."

A. As long as the drop is no longer than half the length of your rope, so does the toss and go method. The advantage of using a block is that it allows you to set the length of the rope to match the drop.

If the drop is longer than half the length of your rope, another rope or pull cord must be employed. You can still join the ropes with the overhand knot, but you will want to block the rappel rope if the two rope diameters differ substantially.

Charly

[bigtoeski]

Great points!! Thanks for the info.

[hitchings]

Is there any real evidence of falling gear getting fractured - especially carabiners? I'v got to believe these are made via a drawing and/or forging process, and should be designed,metallurgically, to have a high toughness with a low tendency to propogate fractures, unlike hardened metals which are strong to a point and may then experience brittle and total failure (e.g., powder actuated fasteners loaded in bending).

[sonnylawrence]

Steve Kesler told me of a study wherein a bunch of biners were not dropped, dropped a few feet, dropped many feet, dropped from a high cliff. The strongest in slow pull testing were the ones dropped from the highest point. The possible explanation is that hitting a surface case hardens them rather than creating micro-fractures.

Has anyone heard of similar studies?

[bigtoeski]

I have only heard of people taking x-rays of their equipment to find hairline fractures internally. Never seen this however. Anyone else know or seen this?

[bigtoeski]

The other downside to dropping equipment is of course the burs that are created which then of course cut the rope.

[bigtoeski]

There is some good information from rockclimbing.com Just search for hairline fracture. Sounds to me like there are microfractures (not seen) and hairline fractures (visible). The visible fractures are of concern whereas if you can't see em then probably don't need to worry about em. Again this information all comes from the internet so take it with grains of salt.

[skianddive]

If there is any danger of the biner in the biner block hitting a rock or getting stuck, you can always use a Knot Block - as described in this link:

http://www.canyoneering.net/forums/showthread.php?t=58&highlight=figure+block

[bst]

You can inspect for fracture with a penetrant inspection kit, available from any machining supply stores and some auto part stores. It is easy to apply in your garage. It is not easy to detect hairline fracture with X-ray.

I don't think a small hairline fracture shows up in a pull test immediately. A small fracture speeds up fatigue cracking.

[rcwild]

Doubt if I could find the article again, because I don't remember where I read it, but ...

It suggested that the concern about using dropped gear for fear of hairline fractures is not as well founded now that most gear is aluminum rather than steel. Steel is a more brittle metal. Aluminum more malliable.

Anyone familiar with the article? Tests done?

[ratagonia]

Not that, AGAIN! These things are like a virus.

Micro fracture occurs - in brittle materials, such as the high tech ceramics used in jet engines. Micro fractures do NOT occur in ductile materials like the aluminum used to make carabiners.

It is possible for cracks to form, however, they are not formed by dropping on hard surfaces. If the gate closes smoothly and there are no burrs across the working surfaces, then your carabiner is just fine.

Why don't we see published test data on this issue?

Well, testing costs money. Proving a negative is a very difficult test to conduct. Who's interest is it in to prove this negative, anyway? If people want to throw away carabiners that fall X feet onto rock (where X might be 2, 10, 1000, 100000000), then the carabiner manufacturers don't really have a problem with it. Even if they drop a bunch of biners X feet and see no decrease in strength, they cannot publish this info. If a biner broke (completely unrelated to this issue), a smart lawyer would be able to construe publication as reckless endangerment.

I know Chouinard Equipment tested biners dropped off the top of El Cap (by mistake). 3000 feet - no problems. They also dropped a bunch of biners 200 feet onto concrete (oil rig maintenance shaft) and it showed no loss of strength.

So. Stop it. Micro-cracking in carabiners - does not exist. Kill it. Stamp it out.

next - My helmet causes cancer because of outgassing!

Tom

[bigtoeski]

Other than maybe being a little more bulky, does the knot block have other downsides to it?

The figure 8 knot ever been known to untie itself with a high load?

[dccampen]

Micro fracture occurs - in brittle materials, such as the high tech ceramics used in jet engines. Micro fractures do NOT occur in ductile materials like the aluminum used to make carabiners.
...
So. Stop it. Micro-cracking in carabiners - does not exist. Kill it. Stamp it out.

Does "micro fracture" have a specific technical meaning? Aluminum alloys will fail by crack propagation and there is a specific phenomenom call Stress Corrosion Cracking. What this means about the integrity of a biner that falls a thousand meters I don't know.

here is a link about SCC in aluminum alloys:
http://www.key-to-metals.com/Article17.htm

more on cracking in aluminum:
http://aerade.cranfield.ac.uk/subject-listing/esdu/ES109.html

http://www.sportdiverhq.com/tanktalk.htm

http://corrosion.ksc.nasa.gov/stresscor.htm

http://www.wahoo2001.com/Divingincidents/dangerous%20tank%20explosions.htm

[hank_moon]

Other than maybe being a little more bulky, does the knot block have other downsides to it?

Yah, try to untie a wet knot block after loading sometime...

[jmart]

Dear Tom,


Not that, AGAIN! These things are like a virus.
Proving a negative is a very difficult test to conduct. Who's interest is it in to prove this negative, anyway?



Can you please tell me what you mean by "proving a negative?"

Okay, someone just had to ask.........

[hank_moon]

Can you please tell me what you mean by "proving a negative?"

Proving the existence of something (e.g. God, micro fractures, etc.) is fairly easy if sufficient evidence can be found. Conversely, proving the non-existence of something is impossible because of the abundance of "non-evidence". In other words, simply "not finding" evidence of something does not mean that it does not exist. Before a live Coelacanth was discovered in the 1930's I'll bet its existence would have been denied by many scientists of the day. Old fishy just showed us that ya never know. Make sense?

[skianddive]

Yah, try to untie a wet knot block after loading sometime...
We were taught that you could put a biner through the Knot Block to make it easier to untie - as illustrated in the link I provided earlier. If you were then worried about this biner hitting a rock when the rope is pulled, you could also use an old rapide instead.

[hank_moon]

We were taught that you could put a biner through the Knot Block to make it easier to untie - as illustrated in the link I provided earlier. If you were then worried about this biner hitting a rock when the rope is pulled, you could also use an old rapide instead.

i wouldn't worry about a 'biner hitting rock - it has never happened to me in 5 years of frequent 'biner block use. Even if it did hit the rock, I wouldn't worry too much as there's no evidence that such small impacts are a concern. Using a knot block AND incorporating a 'biner or maillon sounds like needless bother to me...

[ratagonia]

Other than maybe being a little more bulky, does the knot block have other downsides to it?

The figure 8 knot ever been known to untie itself with a high load?

Yeah, in addition to being hard to untie, the knot has a tendency to get squeezed into the Rapide or ring and get stuck. Depends on the geometry, of course, but it just seems easier to do a biner block than carefully analyze the geometry for potential problems.

Tom

[ratagonia]

Does "micro fracture" have a specific technical meaning?

Probably does. I remember discussion of it in Materials class back in Engineering School, but that was a looooooooong time ago. Google "microfracture ceramic" and you seem to get discussion about abrading coatings. so...

What people talk about is fractures in the material that are so small they are not visible (thus micro) resulting from a hard impact. Part of the fallacy is realizing that compared to the stress of falling at terminal velocity and hitting a hard object, an aluminum carabiner is very strong. The other part of the fallacy is that aluminum does not break this way.


Aluminum alloys will fail by crack propagation and there is a specific phenomenom call Stress Corrosion Cracking. What this means about the integrity of a biner that falls a thousand meters I don't know.

here is a link about SCC in aluminum alloys:
http://www.key-to-metals.com/Article17.htm


Yuppers.

To get SCC, you must have a continuous stress plus a corrosive material.

There has been one incident of SCC that I know of in carabiners. In early 90's, Black Diamond picked up that there were cracks in some Chouinard carabiners. At that time, the pins in the gates were a force-fit (they are now riveted on both sides). The "force" of the force-fit provided the stress. Turns out, the lubricant used for pushing the pins in was contaminated with some sodium, thus providing the corrosive.

Most of the carabiners had a clear crack from the gate pin (the top one, not the hinge one) along the length of the tang. Black Diamond replaced these carabiners to the public (and was paid by the Chouinard Eq trustfund for doing so). Funny thing was, even with a big crack on one side, the strength of the carabiner was not compromised by more than 5%. But, folks don't like climbing with cracked carabiners, so...

So, SCC is unlikely to be a problem on carabiners, unless you find some mid-late 80's Chouinard carabiners (mostly Quicksilvers, as I remember). You can SEE the cracks, worth inspecting for on old carabiners.

Tom

[skianddive]

i wouldn't worry about a 'biner hitting rock - it has never happened to me in 5 years of frequent 'biner block use. Even if it did hit the rock, I wouldn't worry too much as there's no evidence that such small impacts are a concern. Using a knot block AND incorporating a 'biner or maillon sounds like needless bother to me...
I wasn't worried - 'bigtoeski', who started this thread, was worried, and you will note this if you look at the first message. This is the reason that I acknowledged the issue in my post.

Incorporating a 'biner or maillon (or rapide or quick link) into a Knot Block may seem like a "needless bother" to you, but I was merely addressing your issue of how to "untie a wet Knot Block after loading". The addition of one of these pieces of hardware into the Knot Block will "open up" the Figure 8 knot and make it easier to untie after being loaded.

[meuon]

CMI and Petzl have both done extensive testing and studies, and that I have in my hands right now, that show that any 'biner fall that does not disfigure the biner beyond a surface scratch has no effect on the rated strength on the 'biner. I'm going to see of I can get permission to scan these and post them on the web.

That does not mean you should not inspect it carefully, especially the gate functioning and locking as they will sometimes not survive a fall. (Yes, I've dropped a bit of gear.. )

The whole if you "drop a biner replace it story" was created by unscrupulous gear sales-driods to get you to buy more gear.

As for a good figure-8 failing under load: I was attending a rigging course a few months ago where it was officially announced "a figure 8 knot does not require a 'backup' knot".
That does not mean that you can't, and I often do it to dress up a loose end and keep it out of the way. But used properly, I trust figure 8's.

[rudy118]

It seems that if one dedicates a particular biner for the sole purpose of blocking, the question of fractures becomes mute. In the event of a biner cracking all the way and dislodging from the knot block, one would still have a perfectly good knot block pressed against the rap ring.

[rcwild]

I have enough confidence in biner blocks that I see no reason to use a dedicated carabiner. I grab any biner from my gear loop for the block. I will use that same biner for a munter-mule, then part of my ascending system, etc.

Set a carabiner next to a rappel ring or rapide (5/16" is the recommended size for a rapide). Ask yourself if it is physically possible for that carabiner to pass through that ring or rapide. The answer is "no way".

Measure the space (width) inside of a rappel ring or rapide. It's around 1.5 inches for a rappel ring and around 3/4 of an inch for a rapide. The spine of the carabiner is used as a cross-bar against the ring. There is very little leverage because the space inside the ring/rapide is so small.

Should be obvious that you should not rig a block with biner on biner. Two reasons – (1) carabiner can easily pass through carabiner (duh) and (2) the space inside the carabiner used in place of rap ring is much greater than the space inside a ring/rapide so leverage will be much greater.

A couple notes:

1. Tie the clove hitch on the center of the SPINE (aka backbone) of the carabiner, not at the end of the carabiner.

2. Cinch that sucka down before anyone rappels on it. Yes, the weight of the person on rappel will probably cinch it down. Probably?

[rcwild]

In the event of a biner cracking all the way and dislodging from the knot block, one would still have a perfectly good knot block pressed against the rap ring.

I assume you are referring to a previous post about using a figure eight on a bight as the actual block. The description included a carabiner placed inside the knot simply to make it easier to untie. The carabiner will not be loaded.

Not true with a carabiner block. If that's not obvious ... clove hitch is a HITCH. Remove the thing that the hitch is connected to and the hitch ceases to exist.

When I teach blocks, I show students several different ways (knots and biners) and explain the pros and cons of each, then recommend they choose a favorite and master it. The majority of students lean toward the biner block. Hardware good. There seems to be a concern that that figure eight knot could somehow compress enough to squeeze through that small rapide. It's irrational.

If, for some reason, a person is concerned about a biner block failing, you can back it up. Tie a figure eight or butterfly knot a foot below the ring/rapide on the block side of the rope and clip the loop to the rappel side of the rope with a carabiner. That creates a closed loop through the ring/rapide. My confidence is high enough in my CORRECTLY RIGGED blocks that I don't feel the back-up is necessary. But if you need it to achieve that warm fuzzy feeling, go for it. Just don't use your backup as an excuse for getting sloppy rigging your block.

The back-up doesn't need to be de-rigged before the last person comes down. The rope is still retrievable (theoretically), BUT ...

1. You've added more bulk, so be careful not to get your rope stuck.

2. If the rope is in current, it may become twisted, making rope retrieval difficult (impossible).