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

The purpose of this guideline is to assist employers, workers and other workplace parties with understanding the requirements in Regulation 854 - Mines and Mining Plants under the Occupational Health and Safety Act (OHSA) for a seismic risk management program.

Objective

The objectives of this guideline are to:

  • provide information to assist underground mines to identify seismicity and rockbursting hazards and controls to mitigate those hazards
  • provide guidance on what to consider when developing a seismic risk management program
  • assist in controlling and reducing the severity of ground control incidents caused by seismicity and rockbursts, thereby reducing the risk of injury to workers

Legal requirements

Section 71.1 of Regulation 854 under the OHSA sets out seismic risk management program requirements for underground mines.

There are other sections of Regulation 854 that are relevant to the development of a seismic risk management program. These include:

  • Sections 5.1, 5.2 and 5.3 (risk assessment)
  • Section 6 (mine design)
  • Section 65 (communication program)

More information about these sections can be found in the Ground Control Guideline and Risk assessment and management for mines and mining plants guideline.

Background

Numerous fatalities have occurred because of ground instability in Ontario mines. Since 1991, 16 workers in Ontario have been killed in incidents related to ground instability. Of these 16 fatalities, 4 were as a result of rockbursts.

Many of the active underground mines currently operating in Ontario are being developed and operating at greater depths and are at a mine life stage where pillars are becoming more prevalent. Normally, inherent ground stresses increase with depth. The presence of pillars and adverse geological structures often elevates the level of mining induced ground stresses. Therefore, many deeper and older mines are becoming more vulnerable to, and are routinely experiencing more, seismicity and the occurrence of rockbursts.

Ground instability can result from various types of ground failure mechanisms, the two most common being kinematic, or gravity type, failures and rockbursts. Rockbursts involve the sudden failure of a rock mass in which openings or excavations occur and can result in the release of stored energy, often causing the displacement and violent ejection of detached rock. For more detailed information about categories of rockbursts, see the ministry’s Ground Control Guideline.

Throughout 2014 and the early part of 2015, the ministry led the Mining Health, Safety and Prevention Review (the Mining Review) to develop a better understanding of the occupational health and safety needs of the mining sector. A formal risk assessment was conducted as part of the Mining Review which involved the risk-ranking of 263 health and safety hazards which were common in underground mines in Ontario. The top ranked hazard identified through this risk assessment was “rockbursts underground”.

Contents of the seismic risk management program

Threshold for enacting a seismic risk management program

The level of complexity and sophistication of a seismic risk management program will depend on the level of seismicity and rockbursting expected at an underground mine. The level of expected seismicity and rockbursting is determined primarily through the mine design and risk assessment processes.

Stability analyses required by the mine design process (which could include numerical modeling) will reveal those mine locations and stages in the mine extraction sequence where and when high stresses are expected to be induced.

The mine design process will identify the locations of geologic structures, lithological units or changes in lithology that could contribute to seismicity and rockbursting when subjected to induced stresses that are sufficiently high relative to the strength of the rockmass.

Once the regions of an underground mine and the stages in the mine extraction sequence that are prone to seismic hazards have been identified, then risks associated with these hazards need to be determined through the mine risk assessment process. Additionally, the controls that will be required to mitigate these risks need to be enacted.

If, through its risk assessment, a mine employer concludes that there is the potential to generate seismicity and rockbursting that may expose a worker to a hazard, then it must develop and maintain measures to eliminate (where practicable) or to control the hazard. These measures should also be specified in the mine’s seismic risk management program and the communications program required under section 65 of Regulation 854.

If the risk of seismicity and rockbursting at a mine is determined low as to not represent a hazard to workers and controls are not required to reduce it further, then the mine’s seismic risk management program should explain that such controls are currently not required.

The roles of workplace parties

Regarding the development and implementation of a seismic risk management program, several workplace parties at underground mines have important responsibilities, including:

  • owners
  • employers
  • the joint health and safety committee (JHSC) or health and safety representative (HSR)

It is the mine owner’s responsibility, in consultation with the JHSC or HSR, if any, to develop and maintain a written seismic risk management program.

It is also the mine owner’s responsibility to provide a copy of the mine seismic risk management program to the JHSC or HSR, if any, and to review and update the program at least annually. However, a more frequent review and updating may be required in the interim if:

  • through the mine risk assessment, new risks related to seismicity and rockbursting are identified
  • existing controls adopted to mitigate risks associated with seismicity and rockbursting have failed
  • through the mine design process, a new zone or area of the mine is identified which is expected to be seismically active

Controls for mitigating seismicity and rockbursting hazards

As indicated above, the mitigation of seismicity and rockbursting risks should include various controls. Some controls that could be included in the design and production stages include the following:

  • The optimization of mine excavation dimensions and orientations, by determining, through pre-mining stress analyses (numerical modeling), the excavation geometries, extraction sequences and mining methods which are expected to minimize the levels of mining induced stress and the rate of seismic energy release.
  • Selecting, at the design stage, the location, geometry and sequencing of mine excavations that will minimize the adverse stress effects on burst prone geologic structures (faults and dykes) and zones having stiff rock masses.
  • The identification of high seismic risk zones or areas.
  • The selection and utilization of ground support systems that are designed to deform, yield and absorb energy imparted during a seismic event, which are to be installed in regions of a mine that are expected to be prone to seismicity and rockbursting.
  • Application of both micro and macro de-stressing methods.
  • Employment of microseismic monitoring systems.
  • The reduction of workers’ exposure to highly seismic active regions through the use of remotely operated or mechanized equipment.
  • Adoption of re-entry protocols (which specify the criteria and process for allowing workers to re-enter a mine or a portion of a mine to which access has been prohibited due to the increased potential of future seismic events, or following a strong seismic event or rockburst, which is likely to result in damage to the excavation or to the support systems).

A seismic risk management program should identify the controls that are deemed necessary at a mine and should explain how the adoption of such controls will reduce the level of risk associated with seismicity and rockbursting to acceptable levels.

Persons responsible for a seismic risk management program

People in the workplace who are normally responsible for implementing the seismic risk management program at a mine should know about the common causes of seismicity and rockbursting in an underground mine, the typical rockbursting mechanisms and have the skills and abilities to:

  • perform conventional stress analyses to estimate the stress changes that are expected to be induced as a result of the implementation of a mining plan
  • identify hazards related to seismicity and rockbursting and to determine their level of risk
  • identify the microseismic monitoring needs for a mine and to interpret and effectively respond to monitoring results (if microseismic monitoring has been adopted as a control at a mine)
  • design a destress blast (if destress blasting has been adopted as a control at a mine)
  • establish a meaningful re-entry protocol
  • modify or refine an extraction sequence or mining plan to alter the deformation and rock stress change in the affected area
  • modify a ground support design to ensure that it is capable of withstanding the anticipated seismic loading

The workplace parties possessing such skills and abilities would normally consist of:

  • ground control engineers/specialists (typically geotechnical or mining engineers) who:
    • perform pre-mining stability analyses to understand the effects that mining induced stresses and geologic structure could have on the excavations and extraction sequences designed by planners
    • design ground support systems for mine excavations and recommend and oversee ground monitoring programs
  • ground control technicians or technologists who:
    • work with the ground control engineers/specialists
    • install and collect data from ground monitoring instrumentation
    • perform quality control tests on ground support systems

Documenting seismic events and rockbursts

As required by Section 72 of Regulation 854, records must be kept of certain seismic events and rockbursts that occur at a mine. Other documentation and records that should be maintained at a mine would include:

  • microseismic monitoring system results, as well documentation summarizing the analysis of such results (if microseismic monitoring has been adopted as a control at a mine)
  • drawings and diagrams showing the locations of microseismic monitoring sensors (if microseismic monitoring has been adopted as a control at a mine)
  • drawings and diagrams showing the specifications of destress blasting designs (if destress blasting has been adopted as a control at a mine)
  • documentation outlining the details of re-entry protocols
  • drawings and diagrams showing the planned excavations including ground support designs (and any modifications to previous versions)
  • records of the condition of an excavation affected by a seismic event including damage

When the ownership of a mine changes, it is of paramount importance that all of the aforementioned documentation be transferred to the new owner.

Re-entry protocols

Re-entry protocols normally specify the conditions which must be satisfied for allowing workers to re-enter a mine, or portion of a mine, following the occurrence of a strong seismic event or rockburst.

Clause 71.1(2)(g) requires that the seismic risk management program must establish a re-entry protocol following seismic events or rockbursts and set out how and when the re-entry protocol applies. Re-entry criteria should be based on the time it would normally take for the residual effects of a rockburst to return to background levels. Such residual effects can normally be expressed in terms of parameters, such as:

  • the number of seismic events per hour
  • seismic work or rate of energy release
  • cumulative seismic moment, or dynamic and static stress change

While these parameters can be effectively relied upon to estimate a period after which safe re-entry can occur, they must be used in combination with engineering judgement and any other tools such as the records from deformation monitoring instruments, or physical inspections.

Underground mines employing re-entry protocols need to be able to clearly rationalize and explain the basis for allowing workers to re-enter affected workplaces.

Microseismic monitoring systems

Microseismic monitoring systems are an important type of instrumentation relied upon by underground mines that are seismically active to understand where seismicity is occurring and how it is evolving. While microseismic monitoring systems are unable to predict the occurrence of seismicity, they can identify regions of a mine that are seismically active and can be used to calibrate and confirm the findings from stress and other pre-mining stability analyses about where seismicity is likely to occur.

For those areas of underground mines that have been identified as having high levels of seismic risk and activity, the seismic risk management program must set out: how micro seismic activity will be monitored in those areas and how frequently that data will be monitored; and, the measures and procedures that will be used to assess the performance of the system and to maintain the system and its components. Micro seismic monitoring systems should have:

  • a sensor array configuration that covers all active regions of the mine
  • the capability to calculate both the source location and magnitude of microseismic events over the range and frequency of wave forms anticipated
  • the capability to characterize the wave forms generated by microseismic events
  • dedicated technical resources capable of analyzing and interpreting the monitoring results which could be either in house, or obtained from a consulting service provider

Training

Workers and supervisors need to be aware of seismicity and rockburst hazards, the controls that are in place to prevent harm and their responsibilities implementing the controls and participation in the seismic risk management programs.

In general, everyone in an underground mine that may be exposed to seismicity and rockburst hazards must have specific information and training about the nature of the hazards in their workplaces.

For example, workers must also understand their roles in the program and how their work helps to control seismicity and rockburst hazards. Additionally, workers must be informed about where to seek solutions to concerns or answers to questions related to those hazards.

General information and training for workers should include:

  • general information related to seismicity and rockburst hazards
  • education and information on the controls that are in place to minimize the risks of seismicity and rockburst hazards
  • how to raise concerns and utilize the mine ground control communication processes

The program should recognize that different training may be needed depending on a worker’s role in the workplace. Those workers who have more direct responsibilities for implementing the program, such as ground control engineers, technicians, technologists and similar specialists may need additional information. This may include:

  • the requirement for a seismic risk management program and the purpose of the program
  • the identification of the mine locations and stages in the mine extraction sequence where and when high stress changes, likely to trigger seismic activity, are expected to be induced
  • how seismicity will be monitored in the mine
  • the controls that are in place to minimize the risks of seismicity and rockburst hazards and the processes to determine and communicate these requirements

Where an employer at an underground mine is not the owner, the owner and the employer should work together to ensure that workers have information and are adequately trained on the mine’s seismic risk management program. The owner and the employer (if not the same) should consider:

  • how workers are to be made aware of the details of the program
  • how information relevant to the program (pertaining to the mine risk assessment and the mine deign) is to be disseminated
  • issues related to the delivery of training for workers on the program requirements
  • how to ensure that the necessary controls are implemented and remain effective

As changes to the program are made through the annual review, or as otherwise required, workers may require additional training, information and instruction. Documentation and records of all training must be readily available for review at the mine site. Training facilities such as Workplace Safety North (WSN) or the Workers Health and Safety Centre can help workplaces with these training requirements.

Consultation with the committee or representative

Owners must develop and maintain a written seismic risk management program in consultation with the JHSC or HSR, if any (subsection 71.1 (1) of Regulation 854).

Where the OHSA or its regulations require that an action be taken in consultation with another party, including but not limited to the JHSC or HSR, the Ministry of Labour, Immigration, Training and Skills Development expects that the employer will engage in a meaningful interaction (including dialogue, discussion and providing all relevant information) with the JHSC or HSR.

There should be a genuine opportunity for the JHSC or HSR to provide input, and that input should be received and considered in good faith. This includes taking into account any feedback and responses from the JHSC or HSR before taking action (implementing a plan, program, etc.) and responding to any recommendation arising out of the consultation.

Consultation is not simply informing the JHSC or the HSR that the employer intends to take action.

Review of the program

As per subsections 71.1(4) and (5) of Regulation 854, underground mines are required to review the seismic risk management program at least annually, and as soon as possible following either:

  • the identification of any new seismic risks by the risk assessment required under section 5.1
  • the failure of any measure or control for seismic risks required under section 5.2
  • a mine design prepared under subsection 6(1) identifies a new zone or area of the mine that is expected to be seismically active.

The review should consider any changes that have occurred that may affect the program in the intervening period, including any incidents, to ensure that the measures and procedures adequately protect worker health and safety.

As part of this review, mines should create a document for each mine site that outlines a mutually agreeable process between the mine employer and the JHSC or the HSR, and that can be used for record keeping purposes. The employer should ensure that the seismic risk management program is available for review by the JHSC or HSR