12.05.2010

Overturning during relocation

Earlier this week we received photographs of an accident that occurred on a wind farm in Dunbar, Scotland. Having no facts nor indication of when it happened we contacted the crane’s owner Irish based wind turbine specialist McNallys.

It seems that the accident had occurred around eight weeks ago and thankfully no one was hurt. McNally’s was understandably not keen initially to have photographs of one of its cranes published while sitting on its backside.

However the company, which has a solid reputation for doing things right and a correspondingly good safety record, also appreciated the benefits to the industry as a whole to publish the details so that others might learn from the errors that caused the accident as well as ensuring that the facts are understood and tht they accompany the pictures, which were clearly being circulated without the relevant information.
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The crane came to rest on its boom and counterweight

The response from the company was so comprehensive and open that we felt it best to simply publish the information exactly as we have received.

“This incident occurred when the Terex-Demag AC100 was being moved, partially rigged, across a crane hard-stand. The boom was telescoped in, the lifting gear removed and the superstructure was slewed over the rear of the carrier as is normal practice for moving a crane when partially rigged.

Normal practice would dictate that the operator should further proceed as follows:

a) Slew pin engagement, the Terex pin is manually engaged and requires the superstructure to be slewed slowly in each direction to ensure that it is fully inserted.

b) Activation of the slewing brake, this device acts on the slew motor.

c) Superstructure engine switched off, this constitutes good practice.

The operator deployed the slew-pin mechanism but did not slew the superstructure to ensure the pin had dropped fully into place, neither did he check (when dismounting from the cab) that the pin was fully engaged. (this can be seen from the access ladder!) The slewing brake was not activated!

A heavy elastic band had been placed on the control levers to de-activate the “dead-man” switches – these are designed to activate the slewing brake when released.

The superstructure engine was left running – were this switched off the slewing brake would have automatically engaged.
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The crane almost flipped once it gained some momentum

The crane was being shunted on the hardstand (under the control of our crane supervisor) when the superstructure began to slew beyond the carrier centre-line; as the crane slewed out the momentum increased until the crane fell onto its’ own counterweight.

All our lifting operations are carried out with a crane supervisor in attendance, we sign off lift plans and pre-lift check-lists, the operator had more than 20 years experience. With all these measures in place a potentially fatal incident occurred because humans, not robots, drive cranes. Most accidents can be categorised as lack of experience or making too many assumptions - the latter would prove that negligence is a more serious issue than inexperience.

Following the incident we banned all partially rigged crane movements for machines of 130 tonnes capacity or less, we issued a safety alert to all staff and have agreed to share the investigation results with Renewables UK (BWEA) “Lessons Learned Database”.

We treat all incidents in the same manner, the investigation results are used to strengthen our procedures and, more importantly, the information is conveyed to our front line staff; we do not and have not, scoffed at the misfortune of other crane owners – this scenario awaits us all and we will gladly share this information if it prevents a reoccurrence elsewhere.”

Vertikal Comment

There is very little one can add to this as you can see from the photograph the operator had partially extended the rear outriggers, one assumes to serve as stabilisers should the crane have tilted, but it was clearly not sufficient to prevent the crane from tipping.

As always why such an experienced operator should have overridden safety switches and not double checked that the slew pin was engaged is a mystery. In this case he is lucky on that he and everyone else in the vicinity went home to their families that night, it could so easily have been a different story.