This resource does not replace the Occupational Health and Safety Act (OHSA) and its regulations, and should not be used as or considered legal advice. Health and safety inspectors apply the law based on the facts in the workplace.

Purpose

To assist employers, workers, and other workplace parties with understanding the legal requirements in Regulation 854 — Mines and Mining Plants under the Occupational Health and Safety Act (OHSA) regarding the use of ventilation systems in mines and mining plants.

Objectives

  • To provide guidance and information on the requirements for ventilation systems in mines and mining plants.
  • To provide information on the role ventilation systems play in controlling airborne hazards in mines and mining plants.
  • To inform workplace parties about record keeping requirements related to ventilation systems.
  • To provide information on non-ventilated areas in underground mines and the required protections for workers.

Legal requirements

Regulation 854 — Mines and Mining Plants sets out the requirements related to ventilation systems and airborne hazards in mines and mining plants in the following key sections:

  • 182 — requirements for written airborne hazard management program
  • 183.1 -183.4 — requirements where diesel-powered equipment is used in underground mines
  • 184 — requirements for the exhaust systems from internal combustion engines in buildings
  • 252 — requirements for an adequate ventilation system
  • 254 — requirements for heat and cold stress procedures
  • 255 — requirements for areas that are not part of a ventilation system
  • 261— requirements for ventilation for battery charging stations
  • 266 — requirements for dust management
  • 269 — requirements for equipment to detect chemical and physical agents in mining plants

In addition to the obligation to comply with the specific measure and procedures concerning ventilation, mines and mining plants must develop and maintain a written Airborne Hazard Management Program (AHMP) to identify, eliminate and control airborne hazards, or potential hazards, associated with the use of underground diesel-powered equipment, dust, blasting fumes, and other airborne contaminants.

In addition to section 182 which sets out the requirements for an AHMP, sections 5.1, 5.2, and 5.3 of Regulation 854 require employers to conduct risk assessments of the workplace for the purpose of identifying, assessing, and managing hazards, and potential hazards, that may expose a worker to injury or illness.

Under these provisions, an employer must develop and maintain measures to eliminate, where practicable, or control, where the elimination is impracticable, the hazards, and potential hazards, identified in the risk assessment. The employer must develop and maintain these measures in consultation with the joint health and safety committee or health and safety representative, if any.

Background Information

Airborne hazards continue to be a leading cause of occupational disease and illness for workers in the Ontario mining sector.

Ventilation systems are critical in ensuring there is sufficient airflow and air quality to supply fresh air to workers and to dilute and remove airborne contaminants. Ventilation systems need to be properly designed, engineered, installed, and maintained to effectively support the health and safety of workers.

Overview of ventilation systems

To manage airborne hazards in the workplace, mines and mining plants must operate and maintain adequate ventilation systems.

For a ventilation system to be considered adequate, subsection 252(1) of Regulation 854 requires that ventilation systems in both underground mines and mining plant buildings:

  • provide an oxygen content in the atmosphere of at least 19.5 per cent by volume to all workplaces
  • are initiated prior to workers entering the workplace
  • are installed and operated in a manner that does not expose workers to the recirculation of contaminated air
  • are independent of air supplied to operate any drill or machine used; and
  • remove contaminants resulting from the detonation of a blast prior to workers entering the workplace

Ventilation systems can be natural, mechanical or a combination of the two. Regulation 854 does require that certain types of mining workplaces must use specific ventilation systems.

Mechanical ventilation systems

Mechanical ventilation systems are designed to use powered fans to circulate air through ducts, ramps, raises, etc.

Subsection 252(2) of Regulation 854 requires that ventilation systems used in underground mines be mechanical.

Natural ventilation systems

Natural ventilation systems are when air moves from areas of high pressure to areas of low pressure by natural means, such as:

  • temperature
  • barometric pressure
  • moisture content
  • density

Natural ventilation can be used to support ventilation systems in mining plants and other surface buildings by using louvres or vents to increase or redirect natural convection cycles. Controlled openings can make use of natural air flows and create circulation systems.

Effect of external conditions on ventilation systems

Natural ventilation systems are usually difficult to control, fluctuate based on external conditions, are often subject to reversal, and can vary seasonally.

Seasonal changes can significantly impact an underground mine's mechanical ventilation system due to variations in temperature, barometric pressure and humidity. Generally, underground mines are relatively stable in temperature compared to surface conditions. However, seasonal changes can still affect the mine's microclimate.

During winter, when surface temperatures drop, the air entering the mine tends to be colder. Cold air is denser and heavier which can affect the distribution and flow of air within the mine and might lead to a change in airflow patterns.

Seasonal variations can also alter barometric pressure which can affect airflow direction and speed within the mine. High-pressure systems in colder months may increase the airflow into the mine, while low-pressure systems in warmer months may decrease airflow. These pressure changes can impact the efficiency of the ventilation system, potentially causing imbalances and affecting air quality.

In an underground mine, changes in humidity levels can impact the stability of the mine's walls and surfaces, including creating slick conditions. Higher humidity can lead to moisture accumulation, which in turn, might affect the ventilation system's components, such as fans, ducts and airways. Moisture can cause corrosion and degradation which can lead to decreased system efficiency or even mechanical failures.

Local exhaust systems

Local exhaust ventilation systems extract airborne contaminants from the workplace, such as:

  • dusts
  • mists
  • gases
  • vapours
  • fumes

Local exhaust systems are used to control airborne contaminants by capturing them at or near the source. Examples of local exhaust ventilation systems include:

  • smoke eaters
  • fume hoods
  • scrubbers
  • bag houses

Ventilation on demand

Many modern ventilation systems utilize ventilation on demand (VOD). These systems dynamically control the ventilation system on an as-needed basis, using sensors located throughout the mine or mining plant to transmit real-time data on key parameters, such as:

  • equipment use
  • personnel location
  • readings from gas detectors
  • air flow monitors
  • temperature sensors

Design of ventilation systems

All ventilation systems must be designed and engineered for the hazards they are controlling.

Ventilation systems in mining plants, including those that use natural ventilation, may include:

  • air exchangers
  • extraction systems
  • heating ventilation and air conditioning (HVAC) systems
  • roof fans
  • fume hoods
  • doors
  • windows
  • louvres

Ventilation systems in underground mines may include:

  • fans
  • ventilation doors
  • methods of redirecting airflow
  • ventilation raises
  • brattices
  • air movers

Subsection 252(3) of Regulation 854 requires that employers keep and maintain accurate plans of the design of the ventilation system showing:

  • the location of all ventilation fans or openings
  • the location of all ventilation doors, including regulating doors
  • the location and position of all fire doors
  • the location and position of all louvres, brattices, stoppings, regulators controlling airflows and similar devices

Subsection 252(3) of Regulation 854 also requires that employers keep and maintain records showing:

  • the volumes of air in cubic metres per second produced by the ventilation fans
  • the operating gauge pressure of the primary fans
  • at a mining plant building, the volumes of air in cubic metres per second withdrawn by processing equipment
  • at an underground mine, the main direction of airflow

Recirculation

Recirculation is the movement of ventilation air through the same workplace more than once or air that is diverted from the exhaust route and delivered to provide ventilation to another workplace. Recirculation is either controlled, where ventilation air is intentionally passed from the exhaust airway to the intake airway, or uncontrolled, where air unintentionally leaks from the exhaust airway to the intake airway.

In some cases, recirculated ventilation air may form part of a mine or mining plant’s ventilation system. However, controlling recirculated ventilation air is critical as recirculation can concentrate airborne contaminants, such as blasting fumes, dust, methane, diesel emissions, and other hazards such as heat.

Air is considered contaminated when it can no longer adequately dilute and remove airborne contaminants from the workplace. Employers need to ensure that there are procedures in place for monitoring, sampling, and mitigating hazards caused by recirculating ventilation air.

Where diesel-powered equipment is operating in an underground mine, section 183.1 of Regulation 854 requires employers to ensure that a mechanical ventilation system produces a flow of air in accordance with certain specified rules, including where multiple pieces of equipment are operating in a single continuous course of air. The ministry has published a ventilation requirements for diesel-powered equipment in underground mines guideline to help workplace parties understand the requirements for ventilation where diesel-powered equipment is operating.

Underground mechanical ventilation systems

Subsection 252(2) of Regulation 854 requires that mechanical ventilation systems are used in underground mines. These systems generally consist of fans which move air from the surface to underground workings using ventilation raises and ducting.

Underground ventilation fans include three kinds of fans.

1. Main fans

Large primary fans that take surface air and direct it underground. Main fans are responsible for generating the total air flow requirements of the underground mine.

2. Auxiliary fans

Secondary fans that are installed in underground mines to move air to areas off the main ventilation circuit, such as cross cuts, sub drifts, raises, headings, faces, shops, storages, etc. Isolation of the auxiliary fans will not affect the main ventilation circuit.

3. Booster fans

Booster fans are also primary fans and may be installed in both the intake and exhaust airstreams. Booster fans are installed to operate in series with the main fan and boost the air pressure of ventilation air passing through it. Booster fans are typically installed as the mine develops deeper and when the main fan no longer has the pressure or flow capability to service increased resistance.

Areas removed from ventilation systems

Subsection 255(1) of Regulation 854 requires that areas of an underground mine that are not part of a ventilation system be adequately barricaded to prevent entry and have signs posted to warn persons that entry into the area is prohibited. Areas that may be removed from the ventilation system could include:

  • permanently abandoned headings
  • inactive old workings or raises
  • obsolete shops or storages

If workers are required to enter an area that is removed from the ventilation system, subsections 255(2) to (4) of Regulation 854 require that the area must be inspected by a competent person to determine if there is:

  • an oxygen deficiency due to an oxygen content in the atmosphere that is less than 19.5 per cent by volume.
  • the presence of a hazardous gas, vapour, dust, mist or fume
  • any other dangerous conditions

Prior to the inspection, the competent person shall be provided written instructions that set out:

  • the hazards or potential hazards involved.
  • the use of testing equipment required.
  • the personal protective devices that are required to be used or worn.
  • any other precautions and procedures to be taken for their protection.

For additional information, the Ministry has also developed a guideline for working in confined spaces to help workplaces learn about employer and worker requirements when preparing to work in confined spaces safely.

Maintaining ventilation system performance

Ventilation systems in mines and in mining plants need to be maintained to ensure the system is operating as designed. Ventilation systems should be inspected and maintained at a frequency necessary to ensure its proper function. It is important to maintain ventilation systems by:

  • repairing damaged ventilation equipment
  • evaluating the ventilation system’s performance over time
  • inspecting, replacing or maintaining filtration systems
  • inspecting and repairing leaks in ducting, and tears in ventilation tubing
  • ensuring that automated ventilation control systems are operating as designed
  • verifying and calibrating sensors
  • ensuring dampers, louvres, brattices, or vent doors are functioning and in the proper position

Employers must provide workers with information and instruction about the ventilation systems in their workplace. Although the format (written, electronic, etc.) can vary depending on the circumstances, the content of what workers need to know includes:

  • what ventilation systems are in their workplace
  • how and when the ventilation systems need to operate
  • how to identify and report deficiencies within the ventilation systems
  • how to make repairs to the ventilation systems, as may be required
  • what actions need to be taken in the event the ventilation systems are not working