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Safe Main Line Loads on a Single Karabiner Load Sharing Connection

by Alan Sheehan B.E.

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This information is provided for experienced Vertical Rescuers, abseilers, cavers and climbers to help them understand the behaviour of loads applied to a karabiner used in a load sharing anchor (or similar). As technical rope work requires skill (and experience) the author can accept no responsibility for the use or abuse of this information or the consequences of such use. If you use more conservative rigging methods, by all means continue to do so.

The following data assumes a karabiner with axial strength of 2000kgf, a strength across the krab of 600kgf, and the main axis (spine) of the karabiner aligned with the main line (rope).

The following diagram (from Vector Analysis for Vertical Rescuers) illustrates the rig this paper is concerned with.

WARNING! These safe loads do not apply if the karabiner is not oriented correctly to the rope! (ie karabiner spine approximately parallel to the mainline.)

The angles along the top and left of the table are measured in degrees from the line of the rope projected between the slings. The angles along the right and bottom of the table are measured from the rope itself.

Angle |  Loads in Kilograms Force      Safety Factor = 7                      Angle
of    |                                                                       from
this  | Angle of the Other Sling ----->                                       Rope to
Sling V   0   10   20   30   40   45   50   60   70   80   90  100  110  120  Sling
   0    286  286  286  286  286  286  286  286  286  286  286  286  286  286  180
  10    286  286  286  286  286  286  286  286  286  286  286  286  286       170
  20    286  286  286  286  286  286  286  285  267  251  235  220            160
  30    286  286  286  286  251  234  220  198  180  164  148                 150
  40    286  286  286  251  204  188  174  152  133  117                      140
  45    286  286  286  234  188  171  158  135  117  101                      135
  50    286  286  286  220  174  158  144  121  103                           130
  60    286  286  285  198  152  135  121  99                                 120
  70    286  286  267  180  133  117  103                                     110
  80    286  286  251  164  117  101   DO NOT USE SLING                       100
  90    286  286  235  148             ANGLE COMBINATIONS                      90
 100    286  286  220                  IN THIS AREA OF CHART                   80
 110    286  286                                                               70
 120    286                                                                    60
        Angle from Rope to Other Sling ----->
        180  170  160  150  140  135  130  120  110  100   90   80   70   60

Where circumstances and equipment dictate that a karabiner must be used in a load share situation, the following simple rule may be useful. Where the angle between the two slings (ie opposite the mainline) is less than 60 degrees, the karabiner will not fail due to cross loading, and so is safe to the full SWL due to axial loading (eg 286 kgf). If the angle is between 60 degrees and 90 degrees, the krab is safe for up to 200 kgf, and for an angle between 90 and 120 degrees it is safe for only 100 kilograms maximum!

It is recommended that Maillon Rapides of 2000kgf minimum strength be used where possible in these situation. Alternatively, the karabiner can be backed up with another one the same size. This MUST happen if the main load is greater than the safe load listed in the table above. Alternatively the anchor could be re-rigged using an Alpine Butterfly knot to eliminate the need to cross load the karabiner.

SWL's for Cross Loaded Krabs / Alan Sheehan / mailto:als@mail.ix.net.com.au / revised July 29, 1998