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Underground Mining: Ventilation

Safe At Work Ontario
  • Issued: September 2011
  • Content last reviewed: September 2011

Disclaimer: This resource has been prepared to help the workplace parties understand some of their obligations under the Occupational Health and Safety Act (OHSA) and regulations. It is not legal advice. It is not intended to replace the OHSA or the regulations. For further information please see full disclaimer.


During a blitz in October and November, 2011, the Ministry of Labour (MOL) will be increasing enforcement activity related to the Occupational Health and Safety Act (OHSA), and Reg. 854 (Mines and Mining Plants) applicable to mechanical ventilation systems in underground mining operations, and focusing on the supply and maintenance of these systems.

Ministry of Labour mining inspectors will focus on hazards associated with low ventilation volumes resulting from the inadequate supply and maintenance of mechanical ventilation systems. In addition, inspectors will ensure that diesel powered equipment used in underground mines is being maintained according to requirements. They will also check to ensure employers are regularly testing the air quality in the underground mine.

There are approximately 35 underground mines that will be the focus of the month-long, province-wide blitz to commence October 1, 2011. Mines with diesel equipment used for production, development and support of underground mining will be visited by inspectors. Ventilation systems and practices will be inspected to ensure that adequate flows of clean air are being provided and that prescribed substances are below the requirements set out in the regulation. Inspectors will also check that diesel equipment used for underground transportation of workers, materials and blasting of rock is being maintained as prescribed.

Inspectors may take enforcement action if they find violations of the Occupational Health and Safety Act and its regulations.

Priority Areas

Inspectors and will pay particular attention to the following priority areas at each workplace:

  • Mechanical Ventilation Systems
    Employers must provide and maintain a mechanical ventilation system that will provide a partial pressure of oxygen of more than 18 kilopascals to dilute and remove contaminants from underground workplaces. (Subsection 253(1) of Reg. 854).
  • Ventilation Systems Plans
    Accurate plans and records of maintenance for the mechanical ventilation systems must be available at the mine site. (Subsection 253 (2) of Reg. 854).
  • Diesel equipment
    Equipment used for underground transportation of workers and materials and blasting of rock must be maintained as prescribed. (Subsection183.2(1)2 of Reg. 854)
  • Diesel Operating Procedures
    Employers must maintain a chart of procedures for the use and operation of diesel-powered equipment that sets out the actual air volumes and total volume requirements for the equipment in the areas of operations within the mine (Section183 of Reg. 854).
  • Air Testing Requirements
    Employers must conduct weekly air volume tests of haulageways and workings where diesel powered equipment is operating. (Subsection183.2(1)1 of Reg. 854).
  • Air Volume Requirements
    Employers must ensure that a flow of air provided by a mechanical ventilation system:
    • Be at least 0.06 cubic meters per second for each kilowatt of power of diesel-powered equipment operating underground in the workplace. (Subsection 183.1(3) of Reg. 854).
    • Reduce the concentration of toxic substances in diesel exhaust emissions to prevent exposure of a worker to a level of no more than the concentration limits prescribed under section 4 of Regulation 833 ("Control of exposure to Biological or Chemical Agents"). (Subsection183.1(4)(a) of Reg. 854).
    • Reduce the time–weighted average exposure of a worker to airborne respirable combustible dust to not more than 1.5 milligrams per cubic meter of air. (Subsection 183.1(5) of Reg. 854).
  • Dust Control
    Mechanical ventilation systems must be provided and used to dilute and remove contaminants from the underground environment to prevent exposure of a worker as prescribed. (Subsection 253(1) (b) of Reg. 854)

More Information

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