Whilst lifting a particularly long piece of masonry with the gantry crane, the lifting straps slipped. This caused the load to become unstable and slip out of the slings, it fell onto the floor causing it to break into several pieces. No injuries occurred.
Root cause analysis and findings.
Due to the abnormal length of the stone (2.7 metres long) the normal spreader bar used in lifting operations was not appropriate and therefore not used. The overhead gantry crane was being used to lift the stone and as the stone was being lifted the straps slipped along towards the centre of the stone. Consequently, the stone dropped at one end and hit the banker table and a large section broke off and fell to the floor. This then caused the remaining section of the stone to become unstable and fall from the lifting straps.
The angle that the two lifting straps were set at was too shallow (45 degrees or shallower) which meant that during the lifting motion of the crane, one of the straps slipped and moved towards the centre of the stone.
The packing used to protect the edges of the stone where the lifting straps were placed was made of foam and this can slip. Foam is usually preferred over normal cardboard packing as it offers greater protection to the edges of the stone than cardboard does.
The operation of lifting and moving lengths of masonry this size is not a normal occurrence and due to the height restrictions in the mason’s shop, can be problematic.
All personnel involved in the operation have received lifting and slinging training and carry out lifting operations daily and are considered experienced in lifting and slinging operations.