Zip line and tree safety conundrum.

[Tom at Heartwood]

Hello,

 

I was recently asked to inspect the two trees at either end of a zip line and to comment on continued use of the zip line in a private garden. The zip line had been installed some years ago between a sycamore on the uphill end and an ash at the downhill end.

 

The rope is, I think, galvanised steel. It is chokered around the sycamore with with an old tyre to provide some padding at the top side. The wire is now embedded within the stem and the tyre has been partly included. Whilst it is difficult or impractical to non-destructively test the robustness of this set-up my concern is that there will be some inherent weakness and that a potential failure point has been created. Otherwise the tree appears vigorous.

 

The ash tree at the other end has had a hole bored through and the wire passed directly through the stem with a ratchet capstan type tensioning device fitted. The wounds have fully occluded although I guess with use of the zipe line the movement will cause abrasion. As with the sycamore the tree will have been weakened although I don't think that it is practical to judge.

 

The owner is keen to continue to have a zip line in the garden and is interested in suggestions as to how to best go about this. Whilst I am qualified (and insured) to advise on tree safety, the request to advise on the use of the zip line is outside of my experience. My thoughts are to advise that due to early wounding of the tree that the zip line should not be used in its current condition although I am aware that this is a risk averse response. I assume that LOLER testing or similar is required with zip lines and similar installations although I can see that this could be made more complex with living trees as part of the system rather than designed structures.

 

I would be interested to hear of any thoughts or experiences in this area. I guess that there must be many similar installations in gardens as well as tree houses with similar concerns.

 

Cheers,

 

Tom.

 

Tom Dutson, Heartwood Enterprises, Cumbria.

[Goaty]

I hate to see infrastructure affect trees. I would suggest reinstalling it in such a way it can be slackened off annually and moved up and down.

The trees could be eating the metal in a weakening way.

If it's reinstalled with good practice and components. You will be safer as well.

[Loler UK]

Some of the rigging practices by the 'pros' of zip line installation are questionable to say the least, i've known one snap when there wasn't even anyone on it! (the wind loaded the anchor trees they/ one of them and it put so much tension on the line it broke)

 

The 'outdoor education' / high ropes guys have their own training (of sorts) and inspection regimes (of sorts) which seems a tad alien to us in arb let alone Irata. A favoured method of attachment is to use timber running parallel to the trunk with the cable wrapped around that, guy wires can then run from there down to the ground/ lower down on another tree to redirect the forces to run axially through the grain and to minimise any wind loading on the track/ traverse line, another way to reduce the wind loading is to place a second slightly tighter line above the track line as a sacrificial/ indicator wire, too many variables to say much definitive based on your description tbh

 

what method are you using to quantify the loads? the old L x P / 4xRD, or proof loading it measuring the resulting angle and going at it from that end??