Single Point of Failure

מתוך Climbing_Encyclopedia
קפיצה אל: ניווט, חיפוש

נקודה קריטית

A Single Point of Failure or SPOF is a point in a system (in our case, a rope system), that if it fails, the whole system fails. The idea of Single Points of Failure is the basic concept in understanding the application of backup in rope work.

"Even though it contains the word "single", a system may have multiple SPOPF.

In rope rescue situations it is recommended not to have any single points of failure. We eliminate SPOFs by doubling the systems, coupling them or simply backing them up. In climbing, rappelling and canyoning there usually are SPOFs that cannot be eliminated for reasons of practicality and ease of use. Some SPOFs are intentional, like when rapping of a trad route.

A useful exercise for understanding SPOFs is:

List all the SPOFs in a top rope system (solution can be found here).

When the system is build, SPOFs should be analyzed, evaluated and, if needed, eliminated. We know that most failures are due to human errors, either by misjudgment, by wrong application of parts of the system, or by using an altogether unsuitable technique or pieces of gear. A negligible fraction of accidents are due to gear failure.

different approaches to backing up

There are two basic approaches to back up in a rope system:

backup only where it's needed

The first approach is to backing up only where backup is needed. This decision is in the hands of the person who sets up the rig. According to that perception, whether to backup and the mode of backing up are subjective and are highly dependent upon the rigger, his skills and experience, and on the way he sees the dangers.

the points that need backup are of two types: 1. Points that have a higher chance for gear failure. For example:

  • A Biner's gate that is located on a rock edge is pushed against it and can accidentally open. In this case a second, reversed biner would be a proper backup.
  • A webbing or rope that are loaded and pass over a sharp edge or corner with serious risk of cutting. In that case, a second, unloaded (a little longer) rope or webbing will do the trick.

2. Points that are prone to failure due to human error. For example:

  • A locking biner on the harness, that can get unlocked and potentially open. This is backed up wit another connection to the rope (prussik, for example).
  • When setting a belay on a trad route, we use more than one piece of pro.

This approach, in general, requires a high level of skill and knowledge, and is more commonly found in personal activity as rock climbing, alpinism, caving and canyoning. These activities put a lot of emphasize on being lightweight and avoiding bulky systems. For example, it is not considered necessary to backup a a webbing or a biner that are hanging freely and do not touch rock or ice. The assumption is that the gear will not fail by itself.

always backup everything!

The second approach is to have a back up for each and every element in your system. This is looked upon as a rule and is done without using any judgement. Backing up everything minimizes the risk and especially the chances of human error.

This is an extreme statement, of course, and is ridiculous in a way. Backing up everything cannot be taken seriously because:

  1. In most cases you simply cannot backup everything, and even if you could, it's not practical. That means you need to decide what does and what does not need backup, which contradicts the basic demand.
  2. If you back up not all, but too many elements
  • your system becomes bulkier and confusing. This in itself makes you less safe, which again, works against the demand to backup to be safer.
  • you have too much stuff, which makes you slower on the route (in climbing and canyoning). If the weight is not a good enough argument, you also have to spend more time on setting belays and operating them, which also consumes time. Remember, fast is safe.

So what do we do? we backup everything that is not excessively strong. So, all pieces of gear we backup, ropes, biners etc. We would not backup a large tree or a huge building as an anchor even if it is an SPOF.

The principle with this approach is to minimize the effect of the rigger's judgement and so avoid errors. This is common in courses and guided activities, as well as when working with a large number of people: large groups, rescue teams etc.

Contributions to this page were made by Mica Yaniv and others...