There have been 19 serious incidents involving the failure of structures in the mineral mine and quarry sector reported to the inspector in the past year, with a common issue found to be a failure to spot loss of structural integrity as a hazard, and to implement effective controls.

The inspectorate issued 17 compliance actions to control hazards associated with failure of structures across the state in this time.

The issue is not new, with 129 incidents recorded since 2011.

Structural failure is often caused by damage to mechanisms, which can include:

• Corrosion from environmental or chemical sources;
• Vibration from environmental or operational sources;
• Fire and heat;
• Fatigue;
• Interaction with mobile and other plant;
• Adverse weather effects;
• Rot and pest damage;
• Wear and loss of section from operational sources such as the flow of material or fluids;
• Subsidence or erosion;
• Damage and overload from operational sources such as spillage, or from being used in a way other than originally intended;
• Damage and overload from maintenance sources such as landing of heavy items for shutdown maintenance, placing mobile equipment on structures, removal of sections and members; and
• Improper design, construction, installation, modification and repair of structures.

Failure can involve:

• Collapse and sudden failure;
• Partial collapse and instability;
• Failure of individual sections or members;
• Permanent deformation such as buckling and bending of sections or members;
• Cracking in members and weldments;
• Failure of connections and fasteners; and
• Spalling and cracking failures on concrete.

Five of the recent incidents included corrosion of steelwork, failure of a cement silo structure, failure of a conveyor structure, a handrail failure and failure of a raw water tank.

In the first incident, a 1.5m long section of steel weighing 10-12kg detached from a beam and fell 10m from an overhead structure to the floor.

With the failure of the cement silo structure, the support structure for the silo failed, which caused the silo to collapse and strike the control room.

The incident also caused damage to surrounding equipment.

In the third case, the failure of a truss section of the stacker conveyor caused the head end of the conveyor to droop about 2m before coming to rest on the top of the stockpile.

In the handrail failure, a worker was exposed to a 12m fall to the ground when the stanchions of the handrail he was leaning on cracked and the handrail moved.

Lastly, the structural failure of the large capacity water tank caused water to leak out and the tank collapse, which left a worker seriously injured and surrounding equipment damaged.

The inspectorate recommends site senior executives identify all failure of structures as hazards and implement effective controls to protect workers.

A structural integrity management plan should also be developed and include requirements for periodic inspections, audits, testing and reporting on the condition and risk of structures on site.