Summary of incident
On 26 July 2016, a boilermaker working inside a thickener tank during a shutdown died when the gantry above him failed and collapsed, crushing and pinning him against the concrete floor.
The worker had been tasked with removing the thickener’s rake shaft in the centre of the tank. The rake shaft was no longer in use and the rake arms had previously been removed. The rake shaft passed through the feedwell above, and was attached to the motor on the self-supporting gantry bridge that spanned the tank. The feedwell was attached to the underside of the gantry.
As he stood on the tank floor, cutting into the rake shaft, the gantry failed and collapsed, pinning him to the floor. Another worker in the tank who was assisting the boilermaker raised the alarm. Despite the efforts of the emergency services, the boilermaker died from his injuries.
Direct causes
- The gantry bridge had deteriorated substantially due to corrosion and was no longer self-supporting.
- The rake shaft, which was now providing primary support, failed while being cut.
Contributory causes
- The structural integrity of the tank had not been assessed by a competent person prior to work being carried out.
- The boilermaker was instructed to remove the rake shaft, which was not designed to provide primary support.