Underground mining, by its nature, presents a range of health and safety hazards that are different from those in other sectors. Some hazards, such as ground instability, are inherent in the underground environment. Others are introduced through complex mining activities and processes, which bring potential hazards into the underground environment including hazards from mobile equipment such as large vehicles that may limit visibility for the driver. Risks can increase as mines in Ontario get deeper and more expansive. If these hazards are not managed properly using appropriate controls, they can result in serious traumatic injuries, death or occupational illness.

To significantly improve health and safety in underground mining, the Ontario Occupational Health and Safety System partners and mining sector stakeholders need to identify and rank the hazards that pose the greatest risk and warrant the highest level of attention.

What We Heard

The risk assessment process organized by the Ministry of Labour, Training and Skills Development in early 2014 engaged both labour and employers in evaluating and ranking the predominant health and safety hazards in underground mining in Ontario. This process was developed and led by Richard Prial and Dr. Sujoy Dey of the Ministry of Labour, Training and Skills Development specifically to leverage the expertise within workplaces. Using the risk assessment outcomes along with information from the public consultations, written submissions, statistical analyses and Coroner’s inquests, the Review identified five priority hazards, each of which can create a range of health and safety issues:

  • ground control hazards
  • occupational disease hazards
  • hazards associated with water management
  • hazards associated with mobile equipment
  • worker fatigue.

For each hazard, the Review analyzed one specific aspect in detail. The analysis involved exploring different ways to control it, using what is known as the hierarchy of controls, which includes: eliminating the hazard, substituting a less hazardous process, engineering controls that could reduce risk, and administrative and procedural controls. For example, within the ground control hazard, many different aspects could be explored, such as various types of ground failure mechanisms, development heading face instability, ground support issues (i.e. ground support selection, installation and quality control), the monitoring of ground movement, and the rehabilitation of damaged excavation. For the timing being, however, the Review focused exclusively on one particular type of ground failure mechanism - seismicity and rockbursting – because it is becoming a more prominent issue as Ontario mines become deeper.

Malcolm Sparrow in his book The Regulatory Craft footnote 9 highlights the effectiveness of focusing resources on a limited set of issues. As he says, “pick important problems and fix them." The systemic risk assessment process provides the sector and the workplace parties with a list of important problems that need to be addressed. The use of a risk ranking exercise to generate the priority hazards for the system gives the workplace parties the ability to determine priorities. In turn, the priorities allow the health and safety system to focus its efforts on the most important issues for the workplace, which may change over time. Workplace parties can also use the results to determine firm-specific responses to high priority hazards and even compare their internal risk ranking to that of the overall mining sector.


Ground Control Hazards

Over the last 80 years, unmitigated ground control hazards have resulted in the greatest number of traumatic injuries in underground mining workplaces.

In terms of ground control hazards, the Review focused on seismicity and rockbursting and identified opportunities to improve:

  • the ability to identify any predisposition for seismicity and rockbursting at the mine design stage, including better reliance on risk assessment methods and better quality geotechnical data
  • the way microseismic monitoring results are managed, analyzed and interpreted
  • operational controls, including de-stress blasting practices and the use of re-entry protocols following rockbursts
  • research into ways to minimize the occurrence of seismicity and rockbursting in underground mines

To reduce hazards associated with seismicity and rockbursting, an assessment of the risk of seismicity and rockbursting over the expected life of an underground mine must be a critical part of the mine design process. To be able to assess risk, mine design engineers need proper geotechnical data, including accurate information about mine geology and mine-specific stress levels. One effective way to reduce rockbursting hazards would be for the sector to share best practices.

Most seismically active underground mines in Ontario operate microseismic monitoring systems that measure seismic activity and identify potential risks. However, in general, the results from these monitoring systems are in databases that are not always well maintained, which limits the ability of ground control engineers to analyze and interpret this information – or use it to reduce hazards. The mining sector needs dedicated resources to properly manage microseismic monitoring databases so the information can be organized, analyzed and interpreted accurately.

In addition to the information currently required, mine sites should maintain a record of strong seismic events and incidents of ground instability that have occurred, as well as an explanation of the response to each occurrence. This information would enhance efforts to control ground control hazards.

During the Review, subject matter experts indicated that de-stress blasting techniques can be effective in controlling certain types of rockbursting risks in underground mines. However, the theory behind these techniques is unclear. The re-entry protocols currently in place in burst-prone underground mines vary considerably across the province. If the mining sector is going to make optimal use of these techniques, it needs more research into their scientific basis.

Currently, no organization exists in Ontario to oversee and coordinate research into methods for minimizing seismicity and rockbursting or to work with mining companies to adopt new technology to mitigate the risks associated with rockbursting. The Review heard that Ontario needs to leverage the expertise of organizations like the Australian Centre for Geomechanics, which effectively provides that kind of oversight for its mining sector.

Occupational Disease Hazards

While traumatic fatality incidents in the mining sector have declined substantially over the past several decades, deaths related to occupational illness have not.

In terms of occupational disease hazards, the Review focused on airborne hazards such as diesel particulate matter and silica in underground mines and identified opportunities to:

  • raise awareness – among workers and employers - of the importance of controlling risks to health in underground mines
  • increase understanding of the health effects of exposure to diesel emissions in underground mines and improve controls
  • review and update occupational exposure limits (OELs) for airborne hazards in underground mines
  • identify and publicize available options for monitoring ventilation in underground mines in order to reduce concentrations of airborne hazards.

The subject matter experts consulted by the Review share a strongly held belief that the underground mining sector generally puts more emphasis on preventing traumatic injuries than occupational illness. The tendency to focus on traumatic injuries may be due to the fact that workers may not develop symptoms of occupational illness for many years. However, occupational diseases, such as silicosis or various forms of cancer, have serious implications for health and well-being. It is important to limit exposure to hazards that can cause occupational illness including but not limited to airborne hazards, which require effective ventilation systems.

Working in a closed underground environment, miners can be exposed to airborne hazards, such as diesel emissions and silica, putting them at higher risk of developing occupational illness. The Review heard that both supervisors and workers need better education and training so they are more aware of the seriousness of airborne health hazards in underground mines.

Subject matter experts indicated that the sector needs more research to be able to reduce occupational disease hazards. For example, recent research revealed that some components of emissions from diesel powered equipment are carcinogenic. Over the past 20 years, a significant amount of research has been and continues to be done to develop filters to eliminate the harmful effects of diesel exhaust and to identify the optimum diesel fuel type that would result in the least harmful emissions.

In 2004, the Ministry of Labour, Training and Skills Development introduced a review process for establishing occupational exposure levels (OELs) to ensure that these limits are regularly reviewed and updated. Under this process, the Ministry of Labour, Training and Skills Development releases proposals for new or revised OELs (based on the annual recommendations of the American Conference of Governmental Industrial Hygienists) for public consultation. During consultations, stakeholders are invited to submit comments on any or all of the proposed changes. Recent proposals to reduce the OELs for some airborne hazards (e.g. nitrogen dioxide) have prompted serious debate among some stakeholders over the feasibility of implementing the proposed levels. The Review heard that a systematic, scientific health-based review of OELs for a number of key airborne hazards in underground mines would help address the limits and improve health outcomes.

A wide variety of methods are available for monitoring most aspects of ventilation in underground mines. However, the sector currently lacks guidance materials that would identify suitable options for monitoring situations expected to occur in an underground mine. The Review heard that these kinds of guidance materials would be extremely useful for mine ventilation specialists.

Water Management Hazards

Over the last 25 years, fatal injuries related to water management hazards in underground mining workplaces have not declined.

In terms of water management hazards, the Review focused on undesired and problematic water in ore and waste passes and chutes in underground mines and identified opportunities to improve methods currently used to:

  • prevent and minimize the amount of water - both naturally occurring and introduced as part of the mining process - entering underground mines
  • remove water that has entered underground mines
  • safely manage water once it has inadvertently entered ore and waste passes and chutes.

A water management plan is key to reducing water-related hazards. Strategies to minimize the amount of water entering an underground mine include: sealing exploration diamond drill holes that emanate from the surface; and grouting fragmented rock masses that could become a conduit for water transmission. Strategies to enhance capacity to remove water once it has entered an underground mine include: ensuring proper sump and drain hole designs; and having sufficient pumping systems and pump maintenance programs in place.

At the design stage, steps must be taken to ensure that mine water drains away from ore and waste passes and chutes, and that programs are in place to seal holes that intersect these passes. Mining operations must also: institute inspection programs, including camera systems where possible, to detect water that inadvertently enters ore and waste passes and chutes; and put the controls for pass control gates in positions that are safely accessible.

Other elements that would be part of an effective water management plan would include: effectively managing water that has entered ore and waste passes and chutes through operational procedures, and if necessary, procedures for non-routine hazardous tasks; training programs to ensure workers and supervisors are able to recognize dangerous conditions in ore and waste passes and chutes that could result in uncontrolled runs of material; ensuring that inputs into ore and waste passes do not result in uncontrolled runs of material; ensuring that workers operating ore and waste pass chutes or control gates are not endangered by potential runs of material; measuring and recording ore and waste pass content levels; effective communications between mine departments whose activities could influence ore and waste pass and chute contents, performance and conditions; and safe blasting practices for resolving hang-ups in ore and waste passes and chutes involving wet material.

Mobile Equipment Hazards

Over the past 14 years, mobile equipment has displaced ground control issues as the major source of fatal injuries in underground mining.

In terms of mobile equipment hazards, the Review focused on the risks of collision and identified opportunities to:

  • coordinate research into developing line-of-sight (LOS) proximity detection devices and collision avoidance systems
  • enhance understanding of the cognitive impact of LOS proximity detection devices and collision avoidance systems on mobile equipment operators.

Ontario’s underground mines make extensive use of large mobile equipment that can pose a hazard, particularly when the operator’s ability to see other vehicles or pedestrians is obscured. Much work has been done in recent years to develop LOS proximity detection devices and collision avoidance systems. If used properly, these technologies can play an important role in preventing mobile equipment collisions in underground mines. However, the Review heard that, to date, the inventors and developers of these systems have not collaborated effectively to make the kinds of improvements to these technologies that would make them more relevant to mine operators. The Ministry of Labour, Training and Skills Development has begun to address this issue by working with researchers and providing research grants to projects that promote collaboration.

The Review also heard that, regardless of the technology in place to minimize the risk of mobile equipment collisions in underground mines, mobile equipment operators need to have a keen sense of situational awareness. In general, as the level of technology to prevent vehicle collisions increases, the level of operator situational awareness must also increase. Operators must be able to effectively process all of the information provided by the technology and need appropriate training.

Several other practices would also reduce hazards associated with mobile equipment including: using high visibility clothing – a recommendation that has already been implemented; establishing right-of-way protocols; optimizing the use of reflective striping on mobile equipment; optimizing the use and style of strobe lights; establishing communication protocols for accessing production or haulage areas; and developing signage and cap lamp signalling protocols.

Worker Fatigue

Worker fatigue was identified as one of the top concerns in the mining sector risk ranking exercise. Worker fatigue has not previously been a focus of the health and safety system. However, given the current level of concern about this hazard, the Review believes further investigation is warranted.

In terms of worker fatigue, the Review looked specifically at the effect of irregular shift schedules and identified opportunities to:

  • improve understanding of the extent to which worker fatigue has played a part in serious injuries and fatalities in underground mining in Ontario
  • learn from progress other sectors have made in addressing worker fatigue issues.

The Review heard that other sectors, like transportation, have made significant progress in addressing worker fatigue. Studies of how other sectors have developed and implemented successful methods to address fatigue might identify strategies that could be explored and considered in the mining sector.


To mitigate key health and safety hazards in Ontario’s underground mines, the Review developed a series of recommendations that will: strengthen existing legislation; help to focus the efforts of the Mining Legislative Review Committee on the highest risk health and safety hazards in the mining sector; and encourage the development/adoption of best practices and new technology to improve health and safety.

  • 1.1. The Ministry of Labour, Training and Skills Development, supported by all relevant health and safety system partners and subject matter experts, to undertake a Mining Sector Risk Assessment with employers and labour every 3 years.
  • 1.2. The Ministry of Labour, Training and Skills Development to require employers in the mining sector to conduct risk assessments, which would include measures and procedures to control the risks identified in the assessment as likely to expose a worker to injury and illness. The joint health and safety committee, health and safety representative, union, if any, or workers, be consulted on the risk assessment. Employer risk reassessments to be done as often as necessary to ensure programs that result from the assessment continues to protect workers.
  • 1.3. The Ministry of Labour, Training and Skills Development to work with its Research Advisory Council to focus its grants and research on topics that address the priority hazards identified in the Mining Sector Risk Assessment, and disseminate and act upon the findings where appropriate.
    In particular, the Review identified several research opportunities:
    • Defining the scientific basis for de-stressing practices. and developing guidance materials that define best practices for de-stressing
    • Exploring options for collaborating with technology developers to mitigate risks associated with seismicity and rockbursting (i.e. similar to the Australian Centre for Geomechanics model)
    • Defining and quantifying the harmful health and safety effects of worker fatigue in the Ontario Mining Sector, and sectors researching other sectors (e.g. transportation, health care and the military) to see how the mining sector compares, and how the problem has been managed.
  • 1.4. The Mining Legislative Review Committee to align the majority of its work with the major hazards identified in the sector level risk assessment exercise.
  • 1.5. The Ministry of Labour, Training and Skills Development to require that mining employers to address the priority hazards identified in the risk ranking exercise:
    • Enhance ground control protection by identifying key elements in the control of hazards, and requiring employers to maintain a record of significant seismic events in addition to incidents of ground instability
    • Require employers to prepare a formal plan to manage hazards that cause occupational illness, including requirements for worker and supervisor training and communication
    • Require all underground mines employers to have in place a formal water management program
    • Specify that precautions be taken by employers to guard against the accumulation of water in bins, ore and waste passes and chutes
    • Require all underground mines to have in place a formal traffic management plan.
  • 1.6. The Ministry of Labour, Training and Skills Development to review existing occupational exposure limits for a number of key airborne and chemical hazardous substances in underground mines with a view for giving further consideration to the limits for those substances and, if appropriate and advisable, amend Regulation 833. Priority to be given to a review of the occupational exposure limits for silica, nitrogen dioxide and diesel particulate matter (DPM). Other hazards to be considered include sulfur dioxide, and radon.


  • footnote[9] Back to paragraph  The Regulatory Craft: Controlling Risks, Solving Problems, and Managing Compliance. Malcolm Sparrow. 2000.