Get out of here… it's a complete waste of time asking for the break strength of EN 892 dynamic rope! But… if you insist, it turns out to be about 18kN.
Treetools knows this because we stretched a length of dynamic EN 892 climbing line until it finally broke at the base of the knot.
The test involved tying a 1100mm length of Edelwiess Flashlight 10mm dynamic climbing line between two shackles and pulling it to destruction using a 150kN hydraulic ram.The Fisherman knots to the shackle pin used up about 600mm of Flashlight, leaving slightly less than 500mm of free rope between the two attachment points - see inset below.
During the test, the 500mm of rope between the shackles stretched to well over three times this length (approximately 1800mm). The Edelwiess finally broke at the exit point of the Fishermans knot.
In reality, a falling climber would never load the rope to this degree. Simply put, the 'dynamic' properties of the rope would dissipate the energy generated in the fall well before its 18kN breaking point (as it is designed to do).
Having witnessed countless rope breaks, this dynamic rope break-test did present some interesting characteristics.
Firstly, the amount of stretch in the dynamic rope was phenomenal. You can definitely see why it is not used as a tree climbing line.
Possibly of more interest was the behavior of the knot itself. Instead of sucking in the tail, as is normal with EN 1891A ropes, the knot 'absorbed' most of the energy by slowly creeping on the shackle. The relatively short knot-tail barely moved.
When the Flashlight finally broke and contracted on the test bed, the bights, where they touched, fused together completely. The heat generated in the release was at the melting point for the rope - see pic below.
As Treetools has stated previously, the EN892 standard is not common in tree work and a 'break-test' is hardly relevant given the dynamic nature of the rope but it was worthwhile to see exactly how the rope behaved under extreme conditions.
The final breaking point of the EN892 rated Edelwiess Flashlight was not the magical, 'Best Practice ' 22kN figure …but, in our opinion, you could definitely rest you life on it when used as a lanyard!
PLEASE NOTE: EN892 dynamic rope (rock wall climbing/mountaineering rope) should NOT be used as a general climbing line in tree work. This 'break-test' is part of an ongoing discussion regarding the use of EN892 lines as 'energy absorbers' in tree climbing systems. EN892 rope can be used as a lanyard when combined with appropriate mechanical adjusters.
