hunter wrote:I would also keep in mind that a generally accepted rule is to always have two anchor points and there isn't really an exception for one being bomber.
I (and many other cavers, climbers, rescuers, professional rope users, and so forth) disagree. Provided, that is, that our meaning of "bomber" is sufficiently robust.
Suppose you come upon an enormous, well-seated rock that isn't going anywhere. I'm talking something the size of an SUV. (I could go considerably smaller in my example, but this way is the most illustrative.) Suppose you're considering rigging to it in one or the other of two ways:
(1) Tie the rope around the whole thing.
(2) Put two bolts in the front of it, and clip the rope to the bolts.
Unless the rock is sharp at the edges where you'd put the rope around, there's effectively no way that option (2) is safer--in terms of risk of anchor failure--than option (1). If you put bolts in, you could make a mistake judging the quality of the rock you're drilling, you could make a mistake drilling, you could make a mistake putting them in, you could make a mistake and overtighten the nuts attaching the hanger to the bolt...or undertighten them. (Unless you're using one-piece glue-ins...then you couldn't make that specific mistake.) You could make no mistake, but there could be a hidden fracture or weakness you were unable to detect by visual and auditory inspection (though that only very rarely happens). You could put the two bolts too close together (I see this mistake in a very large fraction of horizontally separated bolts placed in walls of northeastern caves). That's a bad thing because (according to
Alpine Caving Techniques), when you put a bolt in the rock fractures a little bit around it, rendering it unsuitable for a placement very close to it.
You could make a mistake tying the big knot around the rock...but then, you could make a mistake tying the more complicated double-loop knot (or if you prefer, pair of single-loop knots) to attach the rope to the bolts.
If the bolts were there in the first place, then they could be corroded where you cannot inspect, or they could have been subjected to an extreme situation (like hitting the hangers really hard with a hammer by accident), or the washers could have been manually overtightened by another party after they were placed.
So, in terms of likelihood of anchor failure, I think it's pretty clear that rigging around the whole boulder has a lower chance of failure than rigging to two bolts on the front of the boulder. And yet you will notice that, by the conventional meaning of the term "redundant" as used in discussions of anchors and rigging,
rigging to the whole boulder is non-redundant, and rigging to the two bolts is redundant. After all, rigging to the whole boulder gives you one anchor point, and rigging to the two bolts gives you two anchor points. As you can see, even the number of anchor points you have in any particular situation is not always so clear, when you think about it hard enough.
So what should you do? Well, it might be that you should rig to the bolts. If they're already there, it's more convenient. If they're not, but you have a bolting kit and bolting skills but want to save rope, then you might consider putting them in (though you should ask yourself if doing so is consistent with your conservation ethic and the wishes of other parties). It might even be safer to rig to them--they might make the rope run at a better angle, or keep it out of some water. But the likelihood of anchor failure is not a reason to use the bolts in this situation (except in the specific case where part of the boulder's surface is dangerously sharp).
You might say, Eliah, this is a contrived example. But is it, really? How many situations are you in where an event likely to lead to the failure of one anchor would not also likely lead to the failure of another anchor? Most bolts are in the same rock
feature, after all. And even if not, if rock turns out to be bad in one place, doesn't that suggest that the natural processes that made it that way might have acted the same way on the wall on the other side of your Y-hang? If you're having a bad day and making mistakes putting one bolt in, aren't you likely to have placed the other bolt on the same day, too? (The same thing goes for a rigger who is just chronically bad at placing bolts--they're the same person for each bolt they place.)
Even if you decide that you really have totally independent, redundant anchors, ask yourself this: How many combinations of any number of anchors are really less likely to fail than a large live tree, rigged around reasonably close to the base? I'd suggest that virtually no anchor is better than this, and that no combination of bolts--except maybe multiple glue-ins placed professionally in previously inspected industrial concrete in the light of day with experienced co-riggers observing followed by frequent formal engineers' inspections--is ever that reliable.
So I agree we should be very, very reluctant to trust a single bolt in a situation where someone could be hurt or killed if it (and no other part of the system) failed. But I think we shouldn't rush to decry nonredundant anchors. Some of the best anchors are nonredundant.