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Updated NSW Technical Reference Guide: Development Of A Spontaneous Combustion Principal Hazard Management Plan For Underground Coal Mining Operations. North Goonyella Case Study

Updated NSW Technical Reference Guide: Development of a spontaneous combustion principal hazard management plan for underground coal mining operations. North Goonyella Case Study

I discovered that in NSW a new Technical Reference Guide (TRG) was issued in March 2021.

The document is the link directly below (100 pages in all)

TRG-Development-of-a-spontaneous-combustion-principal-hazard-management-plan-for-underground-coal-mining-operations-FINAL-for-PUBLICATION (1)

Development of a spontaneous combustion principal hazard management plan for underground coal mining operations 

This new TRG supersedes MDG 1006 Spontaneous Combustion Management Guideline and MDG 1006TR Technical Reference for Spontaneous Combustion Management Guideline.

Over the next week I will go through different new elements to the TRG.

One of the new sections is about the North Goonyella Heating, Fire, Methane Explosion and Sealing at the Surface in 2018.

One of the statements is very interesting

“During the longwall move sequence, a change in gas management focus to reduce elevated methane levels in the 9 North panel, including changes to the mine’s ventilation system to increase airflow, inadvertently intensified the oxidation of coal that was likely causing elevated carbon monoxide levels.”

The Key Learnings and a Description of the Incident are also included further on in this post

The problem in Queensland is that the new TRG and superseded MDG are it is a New South Wales Guide.

It is not referenced under the Queensland Coal Mining Act 1999.

Discussion of key initial learnings

As a result of Peabody’s comprehensive review, the company developed initial lessons and steps to improve the longwall move process and other mining activities.

a) Peabody reviewed ventilation controls and design used during the longwall ‘take-off’ process to minimise the amount of air that entered the longwall panel goaf and interacted with exposed coal remaining within the goaf. Ventilation controls that were put into place in advance of the longwall take-off process may have permitted higher-than-expected volumes of ventilation air to enter the goaf during the longwall take-off process, resulting in oxidation. Gas management and ventilation changes were made in and around the 9 North panel tailgate area in response to elevated levels of methane, which inadvertently intensified the oxidation.

 

b) Evaluate decision-making processes to address the challenges of remotely managing an underground incident solely from the surface. For instance, as the incident approached late September and treatment of the oxidation event escalated, including injection of nitrogen from the mine surface into the 9 North panel goaf, fluctuating gas readings led North Goonyella mine workers and expert third-parties to believe that the treatment plan was likely working due to purging gases from the goaf.

c) Peabody also believed that the system used to monitor and analyse available mine gas data could be improved and better coordinated to identify early stages of oxidation events. Additional training to the appropriate mine workers was implemented to recognise fire gas indicators, gas management and spontaneous combustion, and provide an understanding of a mine’s ventilation history, with a focus on identifying ventilation trends and key indicators of oxidation and developing heating for longwall mines.

d) Peabody modified the longwall removal planning process to reduce the number of days to complete the longwall take-off process to allow for earlier commencement of final sealing, incorporating additional contingency planning in the event the target cannot be achieved. The amount of time the North Goonyella mine’s 9 North panel was idle increased the propensity for oxidation to occur in the longwall panel goaf. Peabody considered additional contingency measures, including installation of pre-drilled holes at the appropriate locations immediately behind the longwall chock line to allow oxygen inhibitors to be injected when longwall advance stops to mitigate against oxidation.

e) Peabody improved the Sealing Management Plan to provide greater clarity around the required steps for sealing the longwall panel (particularly in relation to how these steps interact and relate to the longwall move and re-installation plan). The improved plan provided for the allocation of resources to ensure the sealing management plan is followed as described. Peabody will also provide additional training for underground personnel prior to sealing operations commencing.

f) Peabody honed its system for the management of TARPs to provide clearly defined trigger points, clear explanations of actions to be taken if trigger levels are reached, and improved methods, training and communications involving changing TARPs. Application and progression of TARPs during the longwall take-off process varied from that set out in the Sealing

Management Plan, and communication of TARPs was found to be inconsistent. TARPs describe actions that must be taken by mine personnel in response to observation of certain conditions or triggers (e.g. gas levels) that deviate from normal. TARPs should clearly define their applicability and the required action items when trigger points are reached. 

g) Peabody reviewed the principal hazard management plan (PHMP) for spontaneous combustion and emergency response around the provision of clear and concise guidance in relation to gas readings. The company will also implement a regime for reviewing the PHMP at established intervals and updating as required.

h) Within the Site Incident Management Team (SIMT), Peabody appointed an independent facilitator whose role will be to assist the SIMT in the decision-making process (rather than the technical aspects of SIMT decisions). The SIMT was comprised primarily of North Goonyella mine management personnel, though various other parties also provided input into the SIMT’s decision making process. At times, it was challenging for the SIMT to coordinate and address differing viewpoints from multiple stakeholders. Although these outside parties each play critical roles in responding to a mine emergency, the varied viewpoints need to be effectively managed and facilitated during an incident.

i) Peabody installed quickly closable remote ventilation control devices at each mine drift as they progressed through the reventilation process. In addition, Peabody evaluated options to remotely isolate portions of the longwall panel to provide an option to quickly close these devices after all personnel have been evacuated from the panel.

Peabody’s ability to quickly seal the panel to extinguish the oxidation event before it developed into a fire was impaired once the mine was evacuated and exclusion zones were put in place. Once an oxidation event develops into a spontaneous combustion event, it is difficult to extinguish from the mine surface.

The smaller the area of the mine that is sealed from the source of combustion, the less oxygen is available to support it and the quicker it begins to cool, which should facilitate expeditious recovery. These types of devices could be closed by personnel as part of an evacuation sequence, or through remote means. Emergency seals, which can be installed at chute and gate roads at longwall panels, will also be considered as part of an emergency sealing process (27/03/2019).

Source: May 24, 2019 /PRNewswire/ — Peabody (NYSE: BTU) today announced it is proceeding with the ventilation of the first segment of the North Goonyella Mine in consultation with the Queensland Mine Inspectorate as part of a comprehensive phased reventilation and re-entry plan and expected longwall production in 2020.

 

Case study: North Goonyella 2018

The description of this event is based on the press releases from Peabody Energy. We gratefully acknowledge their permission to republish the details.

On 1 September 2018, during a scheduled longwall move from the 9 North panel to the 10 North panel, an area of the North Goonyella Mine, in a remote area of the Bowen Basin in Australia, began registering elevated gas levels caused by oxidation of some coal. Mine management quickly assessed the facts, took appropriate steps, removed workers from underground, contacted the Queensland Mines Inspectorate and independent industry and scientific experts, and began mobilising resources to correct the situation.

Over a number of weeks, the company worked with industry experts, and in consultation with the inspectorate, to take extensive steps to treat the oxidation from the mine surface. Subsequently, elevated carbon monoxide detected from within the mine indicated oxidation of coal, which can occur when coal is exposed to oxygen for an extended time period. In subsequent days, services such as power, ventilation and water management activities continued. By 16 September, gas levels lowered at times to the point of allowing temporary re-entry by a limited number of workers for inspection and other activities. Surface activities continued, and mine personnel remained at the ready for resumption of the longwall move. (Major equipment and some shields had been moved to the new longwall panel, with about half of the shields and some ancillary equipment remaining to be moved from the completed panel area.)  Gas levels remained variable through this period, with subsequent signs of elevated temperatures and low-level oxidation of coal. The company advanced a progressive plan in an attempt to reduce levels and enable work to resume the longwall move, including drilling additional inertisation holes, pumping additional nitrogen and liquid nitrogen near the face from multiple units and sealing a portion of the mine near the completed longwall area – all from the surface.

On 27 September, mine workers saw dark smoke coming from the mine, indicating a fire in a portion of the underground area. Nobody was underground at the time, and all workers on mine property were safely removed to a perimeter exclusion zone.

In consultation with the inspectorate, Peabody initiated a plan to extinguish the fire and contain impacts at North Goonyella Mine. By 2 October, the mine reported that early indications showed this plan had yielded visible results, with only a slight amount of what appeared to be either steam or white smoke emanating from one mine shaft.

The mine’s review of the incident concluded that areas of the mine demonstrated both elevated methane levels and elevated carbon monoxide levels following completion of coal production in the 9 North panel.

During the longwall move sequence, a change in gas management focus to reduce elevated methane levels in the 9 North panel, including changes to the mine’s ventilation system to increase airflow, inadvertently intensified the oxidation of coal that was likely causing elevated carbon monoxide levels.

Despite sustained efforts to manage the oxidation from the mine surface, including use of nitrogen to create an inert environment within the 9 North panel goaf (the mined-out area in the panel), the oxidation accelerated into a spontaneous combustion event that eventually resulted in the fire.

As a result of the actions taken to evacuate workers in advance of the fire and other controls in place, the incident did not result in any injuries.

By 30 September, a comprehensive plan had been developed. Elements of the plan included:

  • implementing use of a mobile GAG unit – a specialist piece of equipment that generates high-moisture inert gases to displace oxygen supply at a fire zone
  • installing temporary seals into mine openings following completion of risk assessments and using remote-control equipment to pump a fire-resistant expandable material called Rocsil
  • ensuring the area was further isolated by additional drilling and sealing of the old longwall panel
  • working with air quality monitoring experts on a voluntary program of environmental monitoring at North Goonyella, including regular site visits and boundary inspections to assess and analyse air quality data from key points
  • ensuring all aspects of the exclusion zone and other safety protocols were in place and observed and using strict risk assessments for all anticipated plan components.

The company implemented its multi-part plan from the surface. The company permanently sealed the area where high methane levels were concentrated. Three of the mine’s five openings remain temporarily sealed to reduce air flow into the mine.

Extensive monitoring was undertaken and was expected to be helpful in later stages of the incident management. The company used existing bore holes to expand gas level monitoring of the mine. A grid of 35 specialised inground monitors was put into place to identify heated activity within the mine workings. Seismic monitors were in place since 3 October. They did not detect abnormal activity. Specialised cameras provided limited visibility into certain sections of the mine.

Due to the risk of storm activity over the spring and summer days, and as per Peabody’s standard procedure, the mine operated under severe weather trigger action response plan (TARP) protocol to ensure worker safety. Activities on site continue under approved, specific risk assessments.

Peabody President – Australian Operations George Schuller said, “While this was a highly unusual combination of events, Peabody is making changes in systems, processes and training, where warranted, to put into place the improvements needed to successfully move forward from this incident. For example, we have already begun installing remote control ventilation systems at mine entrances.”

Throughout the incident Peabody’s incident management team worked alongside the inspectorate and industry experts to ensure it used the best people and resources.

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