Coal Inspectorate | Bulletin | No.204 V 1 | 05 August 2022

Spontaneous combustion monitoring and response systems

What happened?

Recent analysis into technical reports and audit results has highlighted concerns about how underground coal mines are interpreting guidance to develop their spontaneous combustion Triggered Action Response Plans (TARPs).

Spontaneous combustion events have previously occurred in bord, pillar and longwall mines – some with devastating consequences. The most recent events in 2020 resulted in serious injury to coal mine workers, two gas explosions, and previous events have also resulted in sealing mine workings.

How did it happen?

Investigations into past events have shown that TARPS have been found to be inadequate or applied incorrectly.

Key issues

• Analysis of historical data and technical reports from previous events provides opportunities for review and improvement of TARPs.
• Understanding of hazard scenarios and their controls is continually evolving as monitoring and understanding of hazard scenarios improve and this new information should be applied to TARPs on a regular basis.

Recommendations

Site Senior Executives (SSEs) should direct that the site TARPs are reviewed and endorsed by a suitably qualified expert on a regular basis - ideally annually.

Underground Mine Managers (UMMs) should review and update their spontaneous combustion TARPs against the monitoring and response system metrics below and have the TARP endorsed by a suitably qualified expert.

Reviewing the effectiveness of monitoring and response systems

The metrics in your spontaneous combustion TARP need to be representative of the environmental conditions being monitored to ensure they detect changes in this hazard, and trigger an early response to indicators of a spontaneous combustion event.

Escalation of any of these key gas metrics should be thoroughly tested to ensure that they accurately interpret the atmospheric changes being monitored and measured.

A list of criteria to be considered when developing your spontaneous combustion Principal Hazard Management Plan (PHMP) and TARPs has been developed following analysis of historical events. These key matters should be considered and documented.

1. Review development of your TARPs
• TARPs should follow a technical and risk-based process that includes a relevant cross section of your affected coal mine workers and a third-party expert in spontaneous combustion.
• The process should be documented, and the development process should be part of your Safety and Health Management System (SHMS).
2. Assess the spontaneous combustion propensity of your coal seam
• Consider the assessed propensity from laboratory testing against actual inseam incidents.
• Look at the factor of safety applied when considering this relativity.
• Testing should be undertaken with representative samples for the current and planned workings.
3. Considered the relativity of gas evolution data when developing trigger metrics
• Laboratory derived gas concentrations should be considered with actual seam gas concentrations measured from inseam incident data.
• Consider the factor of safety for reliability of these triggers for gas concentrations and ratios.
4. Review historical data from any incidents at operations conducted in the same seam
• Historical data should be considered in the development of TARP metrics at each trigger level.
5. Assess plans in relation to historical incidents which have not effectively provided appropriate responses to manage the events
• Considered the effectiveness of your response capabilities at each trigger level in your TARP.
6. Consider the effective application of your trigger metrics where more than one spontaneous combustion indicator may be present
• Your Spontaneous Combustion PHMP should effectively consider all circumstances where a spontaneous combustion event could occur at your operation.
• There should be TARPs for all potential spontaneous combustion hazards.
• The TARP should require obligation holders to consider these differences and the changes in other concentrations and trends relevant to trigger metrics.
7. Appraise the relevance of gas monitoring data in your assessment of the potential escalating spontaneous combustion event and consider:
• the recency and frequency of gas data being used from non-continuous monitoring points
• the correlation between the real time and tube bundle monitoring points in the ventilation split - especially at the same locations
• the reliability and accuracy of your gas monitoring systems
• the recency and frequency of calibrating real time monitoring locations
• oxygen deficiency issues on your key real time monitoring locations
• how recently your tube bundle monitoring locations were integrity tested
• the flow and suction pressure parameters on your key tube bundle monitoring locations
• the quality and accuracy of bag sample data obtained from the goaf stream and seal locations.
8. Consider gas data obtained from goaf wells and the correlation of these indicators with the underground gas monitoring data
• Review the appropriateness of your goaf well triggers for increasing oxygen concentrations and decreasing methane concentrations.
• Ensure the trigger metrics correlate where these can be triggered.
• Determine if the risk of either of these metrics being met has been considered with actions that may lead to unintended consequences.
• Considered how to implement the Board of Inquiry recommendation for adding the goaf well carbon monoxide make to the longwall return carbon monoxide make in your longwall return Spontaneous Combustion TARP.
9. Consider the application of Grahams Ratio to gas monitoring locations that have the potential for oxygen deficiency where there is an absence of ventilation currents
• Determine that the technical evaluation has been provided in the application of Grahams Ratio to monitoring locations.
10. Consider the impacts of nitrogen inertisation to your gas monitoring locations and the potential for the 'masking' of key indicators
• Any ‘adjustments’ to Grahams Ratio for nitrogen should be evaluated to determine their validity.
11. Consider the validity of CO/CO2 ratio triggers in your TARPs to consider:
• the influence of CO2 inertisation in your TARP metrics
• the validity of your TARP trigger metrics if they have been developed from laboratory derived gas concentrations
• actual seam gas concentrations measured from inseam historical data for this ratio.
12. Considered the presence of Ethylene in your TARP trigger metrics to determine:
• validity of the trigger levels for evacuation when considering the equivalent temperature required to produce this concentration of ethylene
• recent technical reports that indicate the presence of very low concentrations of Ethylene (0.1ppm) at 40⁰C and 1ppm at 120⁰C
• the correlation with the thermal runaway temperature for your coal seam.