NSW Department of Industry’s mine safety resources regulator recently issued a safety alert following a mine site incident in which a feed hopper suddenly failed.
A plant operator heard an unusual noise coming from the run of mine (ROM) feed hopper.
On inspection, the plant operator found the feed hopper had collapsed onto the plant feed conveyor.
The feed hopper was filled with blended material that was being fed onto the mine processing plant at the time of the failure.
A change in the process of loading material into the hopper from a dump truck to a frontend loader tipping had recently occurred.
The feed hopper collapsed unexpectedly onto the feed conveyor, causing substantial damage to plant and structures.
No workers were in the immediate vicinity at the time of the collapse.
A subsequent investigation found:
some bolts had pulled through the hopper flange
structural bolt holes that were elongated by a hot torch
missing structural washers on bolts
stripped threads on bolts.
A check of the mine’s structural inspection program identified fixed structures at the mine were not being periodically inspected by a suitable competent person.
The alert made a number of recommendations:
Mines should have periodic inspections by a competent structural engineer of any structure that may affect the health and safety of people at intervals recommended by the structural engineer. If there is no period specified by a structural engineer, inspections should be carried out at two-year intervals.
Steel structures should be designed, fabricated and erected in accordance with AS 4100 – Steel structures or AS 3990 – Mechanical equipment – Steelwork and other relevant Australian Standards where applicable.
Fixed bulk material belt conveyors (including their structures) should be designed, installed and maintained in accordance with:
AS/NZS 4024.3610 Safety of machinery – Conveyors – General requirements
AS/NZS 4024.3611 Safety of machinery – Conveyors – Belt conveyors for bulk materials handling
Holes in fabrications for structural connections should not be elongated with a hot torch. Structural washers should always be used along with correct pre-tensioning.