13.06.2007

The full facts

Earlier this week we reported on a near miss with a tower crane in Lurgan,Co Armagh. The accident occurred on a Saturday and one of our readers kindly sent us some very clear photographs with a few details.

With the photos seeming to present a clear picture of what happened and some basic publicly reported information we published details of what we knew and observations from the photographs.

Some of the points we made could have given a misleading impression and we are sorry if this is the case. We can now bring you a full report of this incident which could easily have caused several fatalities.

McNallys Crane hire was asked to provide a 250 tonne crane to help dismantle a Terex/Comedil CT331 tower crane at the Castor Bay Water Treatment Works, near Lurgan Co Armagh.

McNallys dispatched one of its 500 tonne Liebherr LTM 1500’s which was working in the area.

The crane began by removing the tower cranes counterweights, having completed this task it prepared to remove the bulk of the cranes jib.

Tower crane specialists employed by Irish Crane & Lifting who were responsible for taking the crane down, attached the slings to the tower cranes jib and allowed the mobile crane to take its weight.

The pins connecting the jib to the tower were then removed. As soon as the jib was freed from the tower it rotated rapidly from the horizontal to the vertical, with the jib tip pointing up and the base down.
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Saturdays 'incident' in Lurgan

Subsequent investigation of the jib section revealed a major error had been made in the calculation of the jibs centre of gravity for slinging purposes.

McNally says that it has a policy when working with tower crane dismantling to oversize all of the components it uses, including the use of slings that have twice the safe load capacity of that required.

Thus if, as in this case, one of the legs in a two leg sling set, ends up taking all of the load it still has the full safety margin.


McNally’s says that within four hours of the accident being reported it had mobilised a 300 tonner, a 250 tonner and a 100 tonne crane to the site.
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Untangling the tower crane jib at height was no easy matter

A detailed lift plan and method statement were drawn up and the jib was removed safely from the 500 tonner late on Saturday night.

Vertikal Comment

There are some important lessons to be learnt from this near miss regarding the dismantling of tower cranes.

Knowing the sequence for removing a tower cranes components is of course a given, (although still a cause of accidents) but this accident highlights another less obvious point which relates to the confidence in sub contract staff acting as riggers/slingers.

This particular incident could have been disastrous and easily resulted in several fatalities. One thought might be for the mobile crane operator to have the relevant de-rigging pages and diagrams from the cranes manual to hand in his cab.

He could at least then watch out for glaring errors as the tower crane erectors go about their work.

In this case the sling attachment points used on the jib were hopelessly off, so far so that a rigging diagram might have highlighted this to the man in the mobile crane cab if he had a copy of the relevant diagram?