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Dynamic loading and (ultra) static access lines

Richard Tregoweth - Wednesday, December 01, 2010

Yesterday we blogged about the increase in demand for SRT access lines when used in conjunction with mechanical ascenders.

Overnight, Jords from Singapore commented the new Yale Blue Tongue Access Line, designed by John Canning and the late Scotty Sharpe, also made an excellent foot lock line… and this in turn reopened the debate regarding non-rated (EN1891A) foot lock ropes.

Most of you will recall a short lived 'Caution Notice' on the ISA website mid-year regarding ultra-static, Dyneema core foot lock lines and the mandatory use of a suitable shock absorber when foot locking. Nicky Ward-Allen's record breaking climb on (super static) Globe 5000 at the Asia-Pacific TCC in March probably reignited the issue worldwide and the Caution Notice was more-than-likely a direct result of that debate.

Since that time the ITCC Caution Notice has been withdrawn, but we are sure that is not the end of it!

Steven from Treehugs in the Netherlands has asked where the energy goes in the case of a fall on a rope like Yale Blue Tongue Access.

Anonymous sums up the obvious answer with "NEVER BE IN A FALL SITUATION" when ascending (SRT).

The very nature of SRT access with mechanical ascenders produces negligible dynamic force on the rope. However, foot locking presents a different situation - ultra static ropes like Yale Blue Tongue Access do need to be treated with respect.

The Omnitree team, Menno Kluiters and Jelte Buddingh demonstrated the force of a foot lock fall at their recent NZAA Workshop.

Menno foot locked up a short distance on Tree Access and created a small amount of slack in his line. A dynometer was attached at the top anchor to record peak force on the line.

Menno (with harness and equipment) weighed in at 105kg. He created about 100-200mm of slack in the foot lock lanyard and let go. The dynometer pinged at 540kg! That's five time his weight with a relatively small fall.

As an observer, the amount of slack Menno had in the system seemed insignificant. The audience wanted him to climb higher and make a more dramatic fall (and spectacle). In hindsight, it's now obvious Menno had done this before, so he knew not to push his luck!

The moral of the story is: if you are intending to use Yale Blue Tongue Access Line for foot locking, make sure you use a dynamic foot lock lanyard or build in some energy absorption as prescribed by the ITCC… or make sure you don't fall.

Omnitree director Menno Kluiters demonstrating the force generated with a small fall on a foot lock line (in this case Tree Access) at the recent NZAA Climbing Workshop.

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