Mineral Mines & Quarries Inspectorate | Bulletin | No.202 V 1 | 10 June 2022

Integrity of Structures at Mineral Mines and Quarries

What happened?

Since 2011 there have been 129 reported incidents involving the failure of structures in the mineral mines and quarries sector, with 19 of those occurring in the last 12 months. These structural failures have resulted in uncontrolled movements, and falls of objects, persons and, in some circumstances, whole structures. All of these incidents had the potential to cause serious harm to persons.

Five of the recent incidents included:

• Corrosion of steelwork: A 1.5m long section of steel, weighing 10-12kg, detached from a beam and fell 10m from an overhead structure to the floor.
• Failure of a cement silo structure: The support structure for a cement silo failed, causing the silo to collapse, striking the control room and causing damage to the surrounding equipment.
• Failure of conveyor structure: Failure of the truss section of a stacker conveyor caused the head end of the conveyor to droop approximately 2m before coming to rest on the top of the stockpile.
• Handrail failed: A worker was exposed to a 12m fall to the ground when the stanchions of a handrail they were leaning on cracked, allowing the handrail to move.
• Failure of raw water tank: A structural failure of a large capacity water tank caused a significant release of water and collapse of the tank structure, resulting in injuries to a worker and damage to surrounding equipment.

The Mineral Mines and Quarries Inspectorate has issued 17 compliance actions to control hazards associated with failure of structures across Queensland in the last 12 months.

How did it happen?

Though there were a number of contributing factors to the incidents identified above, a common issue has been the failure to identify 'loss of structural integrity' as a hazard and to implement effective controls.

Key issues

Sites with structures must ensure they have identified the failure of those structures as a hazard. Controls should be based on the likelihood and potential consequences of damage to mechanisms and failure modes of the structures on site.

Damage mechanisms can include:

• Corrosion (from environmental or chemical sources, particularly in underground mines)
• Vibration (from environmental or operational sources)
• Fire and heat
• Fatigue
• Interaction with mobile and other plant
• Adverse weather effects
• Rot and pest damage (e.g. termites, rodents)
• Wear and loss of section from operational sources (such as flow of material/fluids)
• Subsidence or erosion
• Damage and overload from operational sources (such as spillage, 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)
• Improper design, construction, installation, modification and repair of structures.

Recommendations

• Site Senior Executives must ensure the failure of structures is identified as a hazard on site and implement effective controls to protect persons.
• Site Senior Executives should develop a Structural Integrity Management Plan in consultation with a suitably qualified person (such as a Structural Engineer) that includes requirements for periodic inspections, audits, testing and reporting on the condition and risk of structures on site.

Additional Guidance

Structures at mines and quarries can include the following:

• Buildings
• Walkways, platforms, fixed ladders and stairs
• Retaining walls
• Processing plant support structures for conveyors, mills, solvent extraction and electrowinning plants, grinding, gravity and floatation cells
• Storage bins, tanks, hoppers and silos
• Bridges and culverts
• Cooling towers and ventilation fan structures
• Winding equipment infrastructure such as headframes, sky-shafts and towers
• Support structures for mine services (surface and underground)
• Shade structures (igloos and similar)
• Dredges, pontoons and ship-loading facilities.