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On Friday we dismantled the tower and loaded it onto a truck to ship it back to Wales. Perfect fit… great relief all around that this worked so smoothly. Pretty sure though that this first time was probably the one requiring most improvisation and flexibility as we are still unfamiliar with the whole running of the tower — I would expect this to get easier as we acquire greater routine.

Apart from that, what a fantastic piece of kit! Just moving around on it gives you ideas of things you’ve always wanted to find out more about, but never had the means… until now!

On day two we found ourselves skirting round torrential cloudbursts… luckily it cleared just in time for the first outdoor session, in which we introduced the tower.

The thought behind the Drop Tower is to give something back to the industry, to create a platform which offers possibilities to improve our understanding of the ways in which we work and to provide the means to do replicable testing. The concept is for the tower to go to a number of events in Europe, probably  three or four, and that at these, asides from the official program, people will be able to do their own testing. The way this would work is that if you have something you think would be worthwhile testing, you get in touch with us, we define a test set up and run the tests at the event. This would be free of charge, the only condition being that the results shall be published and made available to the public.

At the Climbers’ Forum this time we did some background tests, linking back to testing we had referred to in years past, but for obvious reasons were unable to show on site.

We looked at the effect that the angle at the anchor point has on anchor point loading in a single, stationary line configuration. The we compared the peak forces generated when dropping the 100kg test mass into a doubled running line vs. a single, stationary line set up. Next we compared energy absorption of systems by varying a stitched semi-static and a knotted dynamic lanyard between the test mass and the load cell and finally compared the performance  of a couple of mechanical devices.

It was great to have Andreas Detter from Brudi Partner supporting us during the talk, as some of this stuff is not entirely intuitive and he’s just an good person to run a presentation with. Some of the results we were still discussing the following day, trying to make sense of the one or the other figure. Over all a very interesting session, interesting results and the tower was great! So easy and fast to reset the mass, offering loads of attachment options…

What were the results? Well, you should have been there if you want to know 😉

We will be writing these topics up in due course and some of the test need to be re-run to clarify what the variables are… topics for years to come!

Thanks to Knut Foppe for the photographs.

 

This demo that Florim and I prepared together discussed how we attach into the hooks of mobile cranes, i.e. cranes with multi-sheave hook blocks with running cables – as opposed to a single, standing cable  – when positioning slings or chains on trees during dismantling operations. To do so we mocked up two hooks out of wood and rigged them onto the drop tower. The motivation for this talk was really reflecting myself… you know how it goes, crane turns up on site in the morning, everything is hectic anyway, you’re trying to organize the ground crew, the traffic management, placement of the grapple truck and chipper, a site briefing – and when it comes to installing onto the hook, you just attach in in any old way. Well, maybe not quite, but the criteria and the legal situation are were not quite clear to me.

That ambiguity remains: In Europe cranes conform to the machinery directive, so are not PPE. However, with suitable means, a lifting operation can mean lifting people, e.g. with a basket. The Gardeners’ health and safety organisation in Germany, the Gartenbau BG, for instance argue that a harness can also be viewed as a suitable means and by doing so managed to legalize attaching to the hook. In Switzerland you apply for a exceptional permit from SUVA, the Swiss health and safety body, to ride the hook, this will be granted on a case to case basis. In this way, the exact interpretation of the legality of tying into the hook varies from country to country.

Next, Florim and I went to speak to a number of crane companies, which was very interesting. For instance I was unclear about how hooks get specced to cranes. Does this depend upon model or size of the crane? What arguments are there for single vs. double hook, who makes the hooks, how much variability is there in the different models of hooks? Again, this is one of these topics that superficially seems really straight-forward, in truth thug, you can spend a while talking about it. The hooks are specced by the customer based on their needs, the manufacturer of the crane buys them from a hook manufacturers, of which there are three or four world wide and then certifies the crane and hook according to the machinery directive.

Next we started discussing attachment options: What scenarios could we envisage attaching to cranes in? We decided there were two generic situations. First, attachment to crane, placement of chains or slings from hook, transfer and anchor climber to tree, cut limb. The other option is in the case of the felling of a tree that is structurally compromised and a transfer of the climber to the tree is no option. In this case the use of two cranes may be a viable alternative, with one crane being used to lift the load and the second to secure the climber.

We discussed various attachment options, directly into the hook, on the neck of the hook above the gate, to the hook block, backed up options, attached to the neck of the hook as well as to the hook block. There are any number of permutations conceivable, however, I strongly feel it to be advisable to keep you PPE and the load separate, i.e. have the attachment outside of the hook, on the neck of the hook and to establish a back up to the block. If the climber is remaining on the crane, as in option two described above, a permanent back up may be worth considering, running a back up device on a secondary line.

Primarily the aim of the workshop was to clarify that there is plenty to discuss in this matter, to ask questions and to establish some generic red threads that people may want to consider when configuring their systems onto the hook.

Thanks to Knut Foppe for the event photographs.