There have been a number of recent instability issues with telescopic boom-type crawler cranes, with the principle cause of each of the incidents being that the tracks were in the retracted/transport position whilst a slewing activity took place. The failure mode of each incident being that the crane became unstable as there was either insufficient extension or that the boom was elevated, failing to counteract the overturning moment of the counterweights when slewed out of line with the chassis.
Although the HSE has advised that these incidents are not classed as a dangerous occurrence, nevertheless they warrant attention and action to avoid future occurrence. Therefore a safety alert from a manufacturer has been issued to raise awareness and how it can be avoided. Good practice would be that, once in the transport configuration, the crane should not be slewed away from the in-line-with-the-track position. Ideally it should be slew locked ready for manoeuvring or loading onto transport.
Although the cranes affected were from a number of manufacturers, the principle applies to any boom-type crawlers where the counterweights are not removed for transport and the electronic control systems do not recognise the unsafe actions of the operator and the consequent unsafe configuration of the crane. The manufacturing standards have been met as there is no requirement for identification / automatic prevention of this condition being reached. The safety alert should therefore be generalised as a potential issue with any crane of this type and the recommendations in the Sennebogen document should be applicable to all manufacturers of telescopic crawler cranes.
The Sennebogen-issued safety alert can be downloaded here.
