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.