20.06.2007

Crane topples on Tasman Bridge

The operator of a mobile city crane belonging to HighRig crane hire was fortunate to escape unhurt after the crane he was driving tipped forward and dangled precariously over the edge of the Tasman Bridge in Hobart, the state capital of Tasmania.

Please register to see all images

The crane driver had a lucky escape when his crane toppled on the Tasman Bridge

The incident which happened at 10 am this morning (Australian time) closed the five lane, 1,395 metre long bridge over the River Derwent for several hours.

One lane of the bridge was blocked as well as the pedestrian footpath and as part of the crane was hanging over the edge of the bridge, river traffic was also stopped. Only the bridge's guard rail stopped the crane from plunging into the river, more than 30 metres below.

Please register to see all images

The crane was working at the highest point on the bridge - 30 metres above the River Derwent

Larger cranes were brought in to lift the toppled crane, the extended boom of which dangled over the water at the bridge's highest point, pointing almost directly downwards with its load still swinging form the hook.

Police diverted all river traffic away from the area as a safety precaution and closed the bridge completely for four hours as three other cranes righted the stricken rig.

Tasmania's Department of Infrastructure Energy and Resources (DIER) said the crane had been moving underbridge maintenance gantries, when the accident happened. The same crane had carried out this task before.

The DIER and police said the cause of the accident, currently being investigated by Workplace Standards Tasmania, was unknown at this stage. A representative from HighRig said that wind might have been a factor.

Please register to see all images

Tasman Bridge was closed for several hours while rescue cranes righted the unit

The bridge was reopened after being given the all-clear by engineers who checked for structural damage.

“While it was fortunate there was no serious injury, it was obviously a dramatic event which is currently being investigated,'' DIER spokesperson Suzie Jacobson said.

Vertikal Comment

Given that HighRig, a sister company to National Crane Hire, has an excellent record for safety and planning, having won several awards in the past. And given that this specific job had been carried before out using the same crane..... And given that there appears to have been no mechanical failure....

It would seem that the unofficial comment from the crane owner, concerning the wind factor may have some merit.

The gantry could easily have been subject to a gust of wind that increased the radius of the load by a metre or so, this with the dynamic effect could certainly pull such a crane over.

Two things then spring to mind, the possibility of wind gusts under a 30 metre high bridge are high. Thus when planning such a lift a higher factor of safety, in other words a bigger crane, might have been sensible.

Alternatively perhaps the operator had way too much boom outgiven that the working radius does not appear to have been too great and height was of no consequence.

While the cranes load chart may not have indicated a significant drop off in capacity for lifting the load with a long boom at a high angle compared to a short boom at a lower angle, in the case of a swinging load the boom deflection and dynamic effect on the crane would have been substantially greater.

no matter which way you look at it, the evidence would suggest that lift planning/method statement and risk assessement could have been better?