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Unstable rocks

Unstable rocks on the roofs or walls of underground mining excavations are one of the main hazards for mining workers. Drilling, excavation, bolting, under winning, mucking and driving in a mine are particularly hazardous.

An unstable rock that falls from a wall can trap workers if an exit is blocked or cause fractures, internal bleeding or even death. To ensure the stability of an underground excavation and prevent accidents, a good knowledge of the rock must be obtained by carrying out studies and field measurements and by observing the behaviour of the rock during operations. The employer and the worker also have a shared responsibility to implement preventive measures and ensure they are rigorously applied.

Safety rules

 Zero tolerance

If this rules is not followed, the CNESST will stop the work and those at fault will be liable to criminal prosecution.

Zero tolerance sheet: Unstable rocks

The roof, walls and working face of an underground excavation must be sounded and scaled to keep them free of any rocks that may come loose.

Except in a mine containing soluble minerals, the roof, walls and working face of an underground excavation must be washed before sounding and scaling to eliminate any dust.

Plans and specifications drawn up by an engineer are required before undertaking an underground excavation. The plans and specifications must be updated by an engineer as the work progresses.

Other mandatory safety measures

Depending on the tasks to be performed, one or more of the following measures must be taken by the employer to ensure the safety of the worker:

  • while sounding work is being carried out, noisy machines or tools that prevent the worker from hearing the sound of their scaling bar may not be used
  • all entrances to an underground excavation that is non compliant and no longer in operation must be closed. “No entry” signs must be posted at each closed entrance
  • any person who works underground must undergo training in occupational health and safety and hold a certificate to that effect

Before moving into a newly excavated area, the worker must take the time to check if the area is safe. They must:

  • make sure they use scaling bars of appropriate lengths and in good condition. The bars must be able to be used at a maximum angle of 45 degrees
  • make sure the work area is quiet so they can hear the sound of the scaling bar
  • remain on sounded and scaled ground, adopt a stable position and make sure there is a clear space so they can move back suddenly
  • make sure the loose rock falls so as not to bounce back on them, their co-workers or the equipment
  • be aware that a rock may fall upon first contact with the bar
  • make sure safe ground conditions are maintained at all times
  • inspect and sound the ground from the secure area to the newly excavated area