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BACKGROUNDER

Preventing Rock Falls and Bursts in Underground Mines

  • Issued: September 29, 2014
  • Content last reviewed: September 2014
  • See also: Bulletin | Mining

Ministry of Labour inspectors will target hazards affecting the stability of excavations in underground and surface mines during a blitz in October and November 2014.

Inspectors will ensure employers are complying with Ontario’s Occupational Health and Safety Act (OHSA) and its Regulations for Mines and Mining Plants.

Falls of ground or rockbursts occur when rocks become dislodged from the roof or walls of an excavated mining site. Measures known as “ground control” must be taken to stabilize the structure of excavations and prevent falls of ground. There are two types of measures:

  • Design measures that evaluate and adjust how new excavations in a mine will be dug out and supported.
  • Operational measures that ensure new excavations are carried out according to the requirements of the mine design.

Falls of ground and rockbursts are among the biggest causes of serious injuries and deaths in Ontario mines.

A recent risk ranking assessment conducted as part of a provincial Mining Health Safety and Prevention Review found that four of the top five highest-ranked risks related to ground control issues.

Ground control hazards mainly involve workers being struck by falling or toppling rock or by rock that is violently ejected from an excavation’s roof or walls.

Ontario has about 40 underground mines, with about 25,000 workers. Most of these mines are located in Northern Ontario. Several of these underground mines operate at depths approaching 10,000 feet. A wide variety of minerals are extracted from Ontario’s underground mines, including copper, nickel, gold and other precious metals, diamonds, salt and gypsum.

There are also several thousand surface mines in Ontario, with about 20,000 workers. Minerals such as gold, palladium, platinum, nickel, copper, as well as material such as limestone, sand and gravel, are extracted from these mines.

Blitz Focus

During the blitz, inspectors and engineers will visit underground and surface mines across Ontario, including ones:

  • recently reopened or new
  • where previous ground control hazards were observed
  • with a poor compliance history

Inspectors will take enforcement action, as appropriate, in response to any violations of the OHSA and its regulations.

Priorities

In both underground and surface mines, inspectors and engineers will focus on:

Mine design: Inspectors and engineers will check that a proper engineering analysis has been conducted to predict issues that could lead to falls of ground and rockbursts in new or existing excavations in mines. This includes how excavations will be dug out and supported. The analysis must be conducted prior to the start of the excavation. Inspectors and engineers will check that adjustments have been made to the excavation design if the analysis identifies any potential problems.

Engineering report: Inspectors and engineers will check that a professional engineer has analyzed and prepared a report indicating an excavation will not endanger workers’ safety in cases where there is no ground support. The report’s findings would be included in the mine design for work being performed in or around the unsupported ground.

In surface mines, inspectors and engineers will also focus on:

Slope stability: Inspectors and engineers will check that stockpiles of loose material are being maintained at a safe angle of “repose” (natural slope). They will also check that the vertical height of the “face” is not too high and the face is not “undercut” (the floor is not formed of loose unpacked material that is less solid than the walls and ceiling). Inspectors and engineers will also look for hazards involving loose material created by blasting at the working face. Inspectors will also confirm that there is a mine design using sound geotechnical pratices for metallic open pit mines.

Face hazards: Inspectors will check that supervisors have examined the face for any potential or actual hazard to the health and safety of a worker.

Craig MacBride, Minister’s Office, 416-326-7709
Bruce Skeaff, Communications Branch, 416-326-7405

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