Post by dougsanders on Sept 22, 2013 8:29:23 GMT -8
Climbers apply the concept of redundancy without knowing why redundancy offers an incredible increase in safety. An understanding this concept would enable climbers to understand the 'why' and actively apply it when wanting to improve safety.
Redundancy increases system reliability (adds safety, reduces failure.) Importantly, redundancy mitigates human errors, including cognitive bias, which lie behind nearly all climbing accidents.
REDUNDANCY: Given redundancy, the probability of a system failing is the PRODUCT of the probability of EACH component failing. (For the purest we generally don't have true independence; however, we approach it.)
Example: With 2 independent pro legs the probability of the anchor failing is the product of the probability of each leg failing.
P (anchor failing) = P (leg 1 failing) X P (leg 2 failing)
= P (1/10) X P (1/5)
= 1/50
(Given the probability of leg 1 failing = 1/10 and the probability of leg 2 failing = 1/5, the overall probability of system failure is 1/50. The 1/10 and 1/5 are made-up. Not advocating only 2 pieces for an anchor. With a 3rd piece there would be a 3rd factor, etc.)
Common examples of use:
Trad anchors where 3-4 pieces are are placed (SRENE).
Checking each others harnesses.
Two bolts at bolted anchors.
Auto block used while rappelling
Rappel stopper knots.
Extra glove liners.
(Old timers remember when extra sun glasses was one of the 10 essentials; an inclusion that must have mystified most non-climbing recreationists.)
With an understanding of this concept, a party may choose to carry 2 water treatment options where water is contaminated; a team might make sure they have 2 descriptions of a complicated route; and a group might use multiple tools where navigation is an issue. These should be kept by different people.
A climber may place a 2nd piece for a crux near at, or near, their climbing skill level; use enough pieces to keep from decking if any one fails; or, add a temporary 'back-up' to a rappel anchor, making an un-SRENE anchor SRENE. A trip leader might plan a 2nd destination to address poor weather at the primary; make sure one rope lead is able take over in case of leader becoming incapacitated; or, review different sourced route descriptions to facilitate recognition, understanding and accuracy.
Redundancy is not a measure of strength. Redundancy is a measure of system reliability. The terms are are not synonymous. Strength can figure into redundancy. Redundancy is a more precise term than 'back-up.”
Not everything needs to have redundancy. Products of modern design, manufacturing and quality techniques, have failure rates so low redundancy doesn't add any appreciable safety. This would include harness belay loops, carabiners, ropes, 'devices' and the like.
This side of redundancy needs to be understood to assure there is no cognitive dissonance in the climber who, might otherwise, see both redundancy and non-redundancy in climbing, the dissonance keeping them from comprehension and more -than-rote application.
As an illustration, the probability of a bolt (material) failing at a bolted anchor is acceptably low; it's the failure of the bolt placement (human) that leads us to use 2 bolts.
One also sees dissonance when talking about trees and SRENE anchors. Most climbers see trees as 'bombproof' therefore redundancy is un-needed. As an extension, no bombproof anchor needs to be SRENE and SRENE can be selectively applied based on the climbers assessment (bias.) Like non-redundant rap anchors.
Trees are a partial exception to redundant anchors. Tree anchors are primarily found only in WA and B.C. which is probably why there is no 'T' in SRENE. Virtually all trees (except the spindly, sapling, decaying, etc.) can safely absorb fall forces. In this respect they are like manufactured items. It's the anchor leg to a tree that needs to be redundant to assure a single one is is not mis-tied, mis-rigged, gets cut or is defective. (When I finally got this concept we were not talking about trees but about bridge abutments as anchors. LOL)
Redundancy increases system reliability (adds safety, reduces failure.) Importantly, redundancy mitigates human errors, including cognitive bias, which lie behind nearly all climbing accidents.
REDUNDANCY: Given redundancy, the probability of a system failing is the PRODUCT of the probability of EACH component failing. (For the purest we generally don't have true independence; however, we approach it.)
Example: With 2 independent pro legs the probability of the anchor failing is the product of the probability of each leg failing.
P (anchor failing) = P (leg 1 failing) X P (leg 2 failing)
= P (1/10) X P (1/5)
= 1/50
(Given the probability of leg 1 failing = 1/10 and the probability of leg 2 failing = 1/5, the overall probability of system failure is 1/50. The 1/10 and 1/5 are made-up. Not advocating only 2 pieces for an anchor. With a 3rd piece there would be a 3rd factor, etc.)
Common examples of use:
Trad anchors where 3-4 pieces are are placed (SRENE).
Checking each others harnesses.
Two bolts at bolted anchors.
Auto block used while rappelling
Rappel stopper knots.
Extra glove liners.
(Old timers remember when extra sun glasses was one of the 10 essentials; an inclusion that must have mystified most non-climbing recreationists.)
With an understanding of this concept, a party may choose to carry 2 water treatment options where water is contaminated; a team might make sure they have 2 descriptions of a complicated route; and a group might use multiple tools where navigation is an issue. These should be kept by different people.
A climber may place a 2nd piece for a crux near at, or near, their climbing skill level; use enough pieces to keep from decking if any one fails; or, add a temporary 'back-up' to a rappel anchor, making an un-SRENE anchor SRENE. A trip leader might plan a 2nd destination to address poor weather at the primary; make sure one rope lead is able take over in case of leader becoming incapacitated; or, review different sourced route descriptions to facilitate recognition, understanding and accuracy.
Redundancy is not a measure of strength. Redundancy is a measure of system reliability. The terms are are not synonymous. Strength can figure into redundancy. Redundancy is a more precise term than 'back-up.”
Not everything needs to have redundancy. Products of modern design, manufacturing and quality techniques, have failure rates so low redundancy doesn't add any appreciable safety. This would include harness belay loops, carabiners, ropes, 'devices' and the like.
This side of redundancy needs to be understood to assure there is no cognitive dissonance in the climber who, might otherwise, see both redundancy and non-redundancy in climbing, the dissonance keeping them from comprehension and more -than-rote application.
As an illustration, the probability of a bolt (material) failing at a bolted anchor is acceptably low; it's the failure of the bolt placement (human) that leads us to use 2 bolts.
One also sees dissonance when talking about trees and SRENE anchors. Most climbers see trees as 'bombproof' therefore redundancy is un-needed. As an extension, no bombproof anchor needs to be SRENE and SRENE can be selectively applied based on the climbers assessment (bias.) Like non-redundant rap anchors.
Trees are a partial exception to redundant anchors. Tree anchors are primarily found only in WA and B.C. which is probably why there is no 'T' in SRENE. Virtually all trees (except the spindly, sapling, decaying, etc.) can safely absorb fall forces. In this respect they are like manufactured items. It's the anchor leg to a tree that needs to be redundant to assure a single one is is not mis-tied, mis-rigged, gets cut or is defective. (When I finally got this concept we were not talking about trees but about bridge abutments as anchors. LOL)