Originally Posted by
ratagonia
Back up with a meat anchor and only last man at risk = potentially dangerous.
Before delving into the why, let me introduce a concept - the Progressive Failure. A PF is like tearing a sheet of paper a bit at a time. It only actually parts (fails) with the last tug, but each little tug gets it closer to failing.
Most of the systems we encounter are not Progressive Fails, they are Limit Fails. Put too much force on it, and it fails. Put less than that force on it, and it does not fail. So we don't think about Progressive fails a lot, but they do happen.
Buried Deadman Anchors CAN be Progressive Fails, working its way toward failure. I've seen a couple of these in the field, mostly due to non-careful deadman construction. Progressive Failures can occur because: A. the webbing is gradually slipping off the rock; B. the webbing has a cut in it that is slowly tearing; or C. the rocks are rearranging themselves with every tug, eventually leading to failure.
Malia was teaching a class in North Wash. They went to some canyon and built a deadman anchor, and all rappelled off it. All good. Next day, she had the other section of the class for the same canyon. They were running a bit late, so she thought "maybe we should just rappel off this deadman we built yesterday and get on to other tasks..."
But, it was a class, therefore, really should do all the stuff. They broke down the deadman and, to Malia's horror, on the bottom of the pile, the 1" tubular webbing was cut halfway through. Apparently an over-enthusiastic placement of the sharp-edged limestone rock had caused damage. Would the deadman of failed? Maybe not right away, maybe not in a long time - but my life needs more than a maybe.
So.
Your hiking down a canyon, and come to a strand of webbing coming out of the sand? Dig it up, check everything, re-build?
Your choice, kinda. But for me, the answer is yes, every time.
Tom :moses: