Another "the more you know": opposed locking carabiners? consider side loading

[Ben Low]

An accepted method for backing up a rope anchor attachment when using non-locking carabiners (i.e. when climbing) is to use two carabiners with gates opposed, as shown:

Some people take the same approach when using locking screw-gate carabiners. I'm not aware of a rationale for using opposed locking carabiners other than "two is better than one", and there are some who consider it a myth [1].

However, it turns out there is a surprising outcome of using opposed screw-gate carabiners - at least one destructive test of two steel 50 kN carabiners with gates opposed resulted in a breaking load of 24 kN - far less than the rating of even one carabiner alone [Rob Stringer, 5 June 2013, Rope Test Lab forum [2]]. Presumed failure due to side-loading of gate by each carabiner.

Aside: the old (pre 2007) ANSI standard for carabiners only required a side load rating of 1.5kN (the new standard is 16kN, still far lower than the axial rating) [3].

[1] http://www.onrope1.com/Myth11.htm

[2] https://www.facebook.com/groups/RopeTestLab/permalink/573443522678647/

[3] http://www.ultrasafeusa.com/gates.htm

Yours in Scouting,

Ben Low

Venturer Leader
1st Balgownie Scout Group
0407 17 25 21
ben...@balgowniescouts.org.au