Lowering off off a single non-locking carabiner

Title says it.
I’m genuinely curios. What is sketchy in that scenario?
No redundancy of course. But assuming my bolt is 100% (bomber glue in, maybe two, connected by chains) what could possibly happen? I see no way the rope could somehow snap out of the biner when being lowered. And as far as I know, carabiners don’t really break, even more so when only loaded statically. 

Redundancy isn't about stopping what will happen every time, it's about stopping what happens once in a million times. 've been attacked by birds while soloing. I've pulled a rope only to have it coil into a slipknot in midair and catch itself on a fixed head. I've had van sized chunks of solid-seeming boulders completely cleave off while my buddy was traversing on it and almost crush him. Climbing has taught me that you don't prepare for what will happen, you prepare for what won't happen.

The only question left becomes

"is preparing for this thing that's not going to happen going to take so much time or extra work that it will cause other more-likely safety issues?"

and

"Am I in a place in my life where 2 nonlocking biners or 1 locking biner would be such a significant loss compared to one nonlocking biner?"

and finally followed by,

"Oh, I'm just rapping, how about I just use 2" of climbing tape and tape the single non locking biner's gates closed?"

I agree. But I’m wondering what COULD actually happen. What’s the worst case scenario here?

People do this all the time when they find themselves over their head on a climb and have to use a bail biner.  Your scenario sounds like an anchor more than having to bail, so why not just re-thread the chains?

Well, the worst case is probably full failure and a resulting death.  Although unlikely, I think that many people want to reduce the risk, and I think that my life is worth far more than two non-lockers

Mike Shorts wrote: I agree. But I’m wondering what COULD actually happen. What’s the worst case scenario here?

Worst case is you get too hung up searching for ghosts that you forget to have fun. 

Maybe some context. In my home area it’s pretty common to lower off off single non locking carabiners. Just for convenience. Sometimes you leave an old biner at the anchor so noone
has to thread the bolt. I do this all the time and consider it to be safe. However, it seems to freak some people out (redundancy and so on),hence the question. In my opinion this is safe, I can see no scenario where you would actually need a locker or two carabiners when being lowered. But maybe someone here knows more than I do.

Safety in climbing is often taught as a series of commandments. "Thou shalt not" so on and so forth. Many of these commandments are adopted as articles of faith. Thus it becomes heresy in a way, to see someone violate one of those commandments and some of the faithful? They don't like having their own faith challenged by the public displays of others - it freaks them out. Many others take a more pragmatic approach to safety and can quickly adapt to different situations with different solutions, relying on their own judgement to cover the sketch.

Maybe if the rope has a stiff section or a severe twist, it could pop through the gate. Seems pretty unlikely. People bail off of single biners or draws all the time.

If I am bailing off of a sport route, I often throw a friction hitch on the belayer's side of the rope. See graphic:

Kevin said:

"Redundancy isn't about stopping what will happen every time, it's about stopping what happens once in a million times. 've been attacked by birds while soloing. I've pulled a rope only to have it coil into a slipknot in midair and catch itself on a fixed head. I've had van sized chunks of solid-seeming boulders completely cleave off while my buddy was traversing on it and almost crush him. Climbing has taught me that you don't prepare for what will happen, you prepare for what won't happen."

This should be in a "how to learn to climb" instructional book. As a stand alone paragraph.

^^^

One of my "impossible" scenarios arose from throwing a rock into a river (non-climbing). I'd thrown a stick into the river for my retriever and she wasn't seeing it. A rock thrown nearby makes a splash and shows the dog where the stick is.

The golf-ball size rock left my hand at speed. Twenty feet from me it hit a robin in mid-flight, knocking it into the river. Lay me the odds of doing that?

I still feel guilty about hitting her too. I doubt she lived.

Mike Shorts wrote:  
I’m genuinely curios. What is sketchy in that scenario?

As sketchy as the bolt you are lowering off. 

I've seen sport anchors in Europe - two bolts, chain, and a single lowering carabiner, had no qualms about lowering off. Of course, it is somewhat easier to judge quality of carabiner than bolt installation.

When bailing definitely worth following Petzl suggestions posted higher up the thread.

As far as I'm aware, the risks from lowering off a non-locker are unclipping risks.

1) Climber weights the rope from above the carabiner, doesn't notice there is a twist falling across the gate, rope unclips, climber dies.
2) Rope is coily or otherwise develops a twist from obstructions near the top, a twist falls across the gate, rope unclips, climber dies. This is especially possible if the climber temporarily unweights the rope on the way down, e.g. while cleaning draws or encountering a ledge.

Just tape the gate shut if you insist on using a single non-locker. Costs 5 cents and 5 seconds, could save a life. 

Mike Shorts wrote: Maybe some context. In my home area it’s pretty common to lower off off single non locking carabiners. Just for convenience. Sometimes you leave an old biner at the anchor so noone
has to thread the bolt. I do this all the time and consider it to be safe. However, it seems to freak some people out (redundancy and so on),hence the question. In my opinion this is safe, I can see no scenario where you would actually need a locker or two carabiners when being lowered. But maybe someone here knows more than I do.

I do this regularly too at local crags. I think most of the fear is overblown. All the failure scenarios are unlikely, although it's probably good to be aware of them.

People in Frankenjura also lower off and clean from single bolt anchors and there aren't more accidents compared to other areas and I haven't heard of any accidents specifically related to that.

When you learn to climb in a gym in a safe and ideal controlled environment, and are taught about redundancy in anchors etc., any deviations from that are perceived as dangerous even though that perception isn't necessarily based on experience or reliable data.

There's also older mountaineering guides who set up belays on a single good bolt when they encounter one, because they consider those to be bomber and the likelihood of failure small enough, and often much better than anything else they could rig on certain climbs.

Mike Shorts wrote: I agree. But I’m wondering what COULD actually happen. What’s the worst case scenario here?

I don't know about lowering, but I've had the rope free itself from single wiregate more than once. Off the top of my head it happened last year from my redirect piece above a belay (belaying my second up from below) and I ended up with the belay coming straight off my harness instead of running up above and back. Not 100% sure how that happened but my hunch is a loop of slack managed to push the wiregate in and slip out. 

Mike Shorts wrote: I agree. But I’m wondering what COULD actually happen. What’s the worst case scenario here?

Like has been said, a loop/cool of rope can get caught on the gate and pop it open. Even in weighted lowering situations (such as lowering a haul bag from one anchor to the next via a redirect) I've seen this almost happen when using just a quick draw as the lowering redirect.

Another would be a situation where you stop lowering and unweight the rope which could again allow a kink/coil to work its way against the biner. (but I would never do that! - think about it realistically, how many times have we stopped being lowered to work part a of a pitch again, or stopped on a ledge to "real quick" take care of something like a rock in your shoe or something, most of us have done this many times while being lowered and most of us never considered to think about the anchor and whether this change in procedure could cause an issue. We become complacent with our systems because "they've always worked" until now, which is why a lot of safety rules are "thou shalt nots" because yes we always intend to consider everything again when we change a practiced procedure but do we always always do that every single time?)

I hate birds. Birds can and will do anything and I don't need to think of a scenario where a large enough raptor messes with the single biner and causes an issue because when it comes to birds and ring tailed cats and marmot, there's nothing those demon spawn aren't able to make happen.

When trying to figure out "what could happen" the trick is not to think about what could go wrong if everything goes as planned. The trick is to think, what are situations that arise where the normal rapping procedure changes? That is where you find the things our thou shalt safety rules are trying to mitigate

Pino Pepino wrote:

I do this regularly too at local crags. I think most of the fear is overblown. All the failure scenarios are unlikely, although it's probably good to be aware of them.

People in Frankenjura also lower off and clean from single bolt anchors and there aren't more accidents compared to other areas and I haven't heard of any accidents specifically related to that.

When you learn to climb in a gym in a safe and ideal controlled environment, and are taught about redundancy in anchors etc., any deviations from that are perceived as dangerous even though that perception isn't necessarily based on experience or reliable data.

There's also older mountaineering guides who set up belays on a single good bolt when they encounter one, because they consider those to be bomber and the likelihood of failure small enough, and often much better than anything else they could rig on certain climbs.

I'm reckon the statistical incidence of single bolts failing is much lower than the incidence of ropes managing to slip out of a single non-locker. 

Andrew Rice wrote:

I'm reckon the statistical incidence of single bolts failing is much lower than the incidence of ropes managing to slip out of a single non-locker. 

That's true, I was just using this as an example of differing risk perceptions. Still, the chance of a rope slipping out of a single non locking carabiner while you're being lowered and the rope is constantly under load is very low and a negligible risk for everybody that willingly drives a car to the crag.

Hangdog Steve wrote: Maybe if the rope has a stiff section or a severe twist, it could pop through the gate. Seems pretty unlikely. People bail off of single biners or draws all the time.

If I am bailing off of a sport route, I often throw a friction hitch on the belayer's side of the rope. See graphic:

has anybody actually fallen onto a prusik?? i have always been so skeptical of this technique.

Pino Pepino wrote:

That's true, I was just using this as an example of differing risk perceptions. Still, the chance of a rope slipping out of a single non locking carabiner while you're being lowered and the rope is constantly under load is very low and a negligible risk for everybody that willingly drives a car to the crag.

I think what you said is true. However, there are plenty of people getting lowered when the rope is not guaranteed to be under constant load. 

L Kap wrote: Just tape the gate shut if you insist on using a single non-locker. Costs 5 cents and 5 seconds, could save a life. 

This. 

You'll find taped single biners on various odd ice routes all around the Wasatch.  You're welcome. 

Helge L wrote:There's also older mountaineering guides who set up belays on a single good bolt when they encounter one, because they consider those to be bomber and the likelihood of failure small enough, and often much better than anything else they could rig on certain climbs.

Even on the old 1/4" buttonheads!  Old doods are nails tough.