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Metropolitan Mine gas inundation causal investigation
This presentation focuses on the investigation to identify the circumstances that required the unplanned withdrawal of workers from the Metropolitan Mine and the reasons for the prolonged period required to establish safe mine re-entry conditions.
Metropolitan Mine gas inundation causal investigation
- 1. David Gordon –Inspector of Mines Coal 29th Electrical Engineering Safety Seminar November 2019 Workers Evacuated After Gas Levels Rise Metropolitan Colliery – 21st March 2019
- 3. • 6:00pm theissue began with the longwall face being stopped on high CO2 in the LW return. • 7:15pm withdrawal of all underground persons begins. Withdrawal TARP activated due to rising CH4 levels. • 8:45pm all persons underground withdrawn to the surface and accounted for. • LW return recorded CH4 to 16.1%, CO2 to 15.9% and O2 to 13.5% in 43m3/s. • Main upcast shaft recorded CH4 to 3.01%, CO2 to 4.16% in 280m3/s. • Workforce out of the mine for seven days. • 2.9 million cubic metres of gas released in 6 days. 38% CH4 and 62% CO2. Facts
- 4. Gas trends –LW return tube bundle
- 5. Gas trends –LW return real time
- 6. Gas trends –Upcast shaft tube bundle
- 7. Gas trends –Ellicott diagram LW return
- 8. Gas trends –Ellicott diagram upcast shaft
- 9. Where did thegas come from?
- 10. Where did thegas come from?
- 11. Withdrawal due toprevious gas issues
- 12. • Most likelysource appears to be from surrounding strata below the working seam. • Limited data available for the mining area. • Gas assumed to be released by a combination of factors • Fracture profile around the LW • Change in depth of cover • Mining through a syncline • Loading event on the supports • No identified geological structure in the immediate area • No cross measure drainage holes due to lack of identified geological structure • Tube bundle gas monitoring continued to function • Real time gas monitoring very limited Findings
- 13. • 1. Managingthe gas reservoirs around extraction panels: • a. Ensure there is enough reliable exploration data available to determine the geotechnical risks and gas reservoir affected by the proposed mining method. • b. Include a means to determine which reservoir the gas is released from to confirm design and modelling assumptions. • c. Include lithology above as well as below the intended working seam. • d. Consider significant gas capture with the gas drainage process and have minimal contamination of accessible mine airways. Recommendations – focusing on
- 14. • 2. Withdrawaltrigger action response plans (TARPs): • a. Design TARPs to reflect realistic triggers and actions that are simple to follow. • b. Develop a process to ensure the workforce are aware and understand the TARPs in use at the mine. • 3. Use of self-contained self-rescuers: • a. Consider expanding the training on self-rescuers to include use during times where low oxygen environments are encountered and excessive levels of carbon-dioxide gas. • b. Develop TARPs in relation to the circumstances when self-rescuers are expected to be used. Recommendations – focusing on
- 15. 4. Post incidentmonitoring: • a. Mines should conduct a risk assessment to determine atmospheric monitoring requirements post incident (explosion, fire, gas event, etc.). This should include both real time and tube bundle. • b. The selection of post incident monitoring arrangements should consider the post incident survivability of the system and system elements. • c. Post incident monitoring arrangements should operate effectively when power is removed from all or parts of the mine. • d. Post incident monitoring points should be installed in optimal locations such as intake airways, return airways and escape routes. • e. Monitoring for gases relevant to the incident should form part of the post incident monitoring arrangements. This should ensure the concentration range of the gases being monitored are appropriate. • f. Implement a program of testing the effectiveness of the post incident monitoring arrangements. Recommendations – focusing on
- 16. 5. Re-entry procedures: •a. Mines should conduct a risk assessment to determine re-entry conditions appropriate for the various risks identified. • b. Develop TARPs to reflect acceptable and unacceptable conditions. 6. Workers’ access to return airways during extraction activities: • a. Mines should conduct a risk assessment to determine the controls necessary for workers to safely access return airways. • b. Develop a procedure to reflect those controls identified. • c. Consider the timing of access, barometric change effects, production activities, whether working alone is appropriate, remote workings, communications and gas detection. • d. Review requirements for appropriate gas monitoring, communications and emergency escape for those workers accessing return airways in the event a withdrawal is required. Recommendations – focusing on
- 17. 7. The determinationof acceptable methane levels passing through the ventilation fans: • a. Mines should conduct a risk assessment to determine the maximum levels of methane that will be allowed to pass through the main ventilation fans. • b. Develop TARPs to guide workers at the mine in the decision-making process when excessive quantities of various gases are being exhausted from the mine. • c. Explore options to be able to conduct simple ventilation changes remotely from the surface to manage unexpected gas issues underground. • d. Explore options to be able to remotely limit the volumes of methane gas levels that pass through the fan infrastructure. Recommendations – focusing on
- 18. 8. Management ofventilation fan exhaust gases around surface infrastructure: • a. Mines should conduct plume modelling in relation to the main surface ventilation fans. • b. Conduct hazardous area assessments to include relevant infrastructure that may be affected by these exhaust gases. 9. Review site emergency management and withdrawal procedures: • a. Include accurate monitoring of the locations of workers and man transport vehicles to facilitate timely and efficient withdrawal. • b. Include the availability of man transports in work areas. Recommendations – focusing on
- 19.
Editor's Notes
- #2 Ladies and gentlemen. I am here to present a brief outline of the results of the Resource Regulator Causal Investigation into the evacuation of persons from the underground workings at Metropolitan Colliery as a result of significant increased gas levels in the return airways from LW303 on evening of 21st March 2019. I will start by showing the animation of the event completed by Coal Services Virtual Reality department. These people are a very talented group and did a very good job as you will see. How many have seen this animation?
- #4 These are the facts. Read them off.
- #5 LW303 return tube bundle monitoring results are shown here on a trend graph of the gas levels prior to the event and during the event. Green is the Oxygen, Light blue is the Carbon dioxide, and Red is the methane. Describe gas levels before, during and after. Following a risk assessment and ventilation modelling, limited site resources made some ventilation adjustments underground on the evening of the 27th March. These changes increased the ventilation quantity into the LW303 circuit reducing the methane to less than 2% and stabilised at 1.7%. Another risk assessment process was conducted prior to re-entry of persons underground on 28th March. Note dilution at end after 6 days following UG ventilation adjustments.
- #6 Note the real time gas reading limitations and the short duration of the UPS. Real Time monitoring limited to the 5% for methane (red) and carbon dioxide (blue).
- #7 Tube bundle gas trends for CH4 (blue) and CO2 (red) here. CH4 to 3% CO2 to 4.16%
- #8 The Ellicott diagram is an indication of the combustibility of the environment sampled. Here the LW303 return quickly moves from a Fuel lean inert environment, through the Combustible zone into a Fuel rich inert zone. As the gases are slowly diluted the trend gradually reverses back through the Combustible zone returning to the Fuel lean inert zone.
- #9 This is the trend for the upcast shaft. As you can see this was trending towards the Combustible zone but did not make it there. However a large section of the return airways between here and the LW303 would have bee in the Combustible zone.
- #10 This diagram represents the theoretical fracture profile around LW303 face area. The working Bulli seam is at the top with the fracture profile affecting around 50 m below through other coal seams and their interburden.
- #11 This is a diagram representing the estimated quantity of gases and where they may have came from. 16% from coal seams, and 84% from interburden.
- #12 The event of 21 March 2019 had a peak gas flow almost eight times greater than any previous event recorded at Metropolitan Colliery. It is concerning the event occurred unexpectedly and with no recognised associated geological structure.
- #13 Read findings.
- #14 Knowing details of the resource gives the information on the risks and therefore an idea of the controls needed. Read recommendations
- #15 At item 3 discuss briefly the persons in the LW27 bleeder return. XAM download indicated 4.89% CO2, 3.92% CH4, 19% O2. When would you use a SCSR? Do you consider low oxygen environments in your decision?
- #16 What is the risk at the mine? How much gas could you have? Level 1 exercises in Queensland have already identified many times that Carbon monoxide Real Time monitors are limited at 50ppm maximum range.
- #17 Read
- #19 One of the issues you can take away from here is to ask your management what has been done as a result of a site review of these recommendations? Do they all or some apply to your mine?