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Coal Inspectorate | Alert | No.402 V 1 | 18 November 2021

Introduction, inspection and maintenance of gas detecting and monitoring equipment

What happened?

Incidents have occurred whilst undertaking maintenance tasks associated with the gas monitoring systems.

  1. An incident occurred at an underground coal mine where a Longwall CH4 sensor was being relocated from a powered roof support to another location along the faceline. When the sensor was disconnected, the tripping circuit failed to operate.
  2. An incident occurred at another underground coal mine where an ERZ/NERZ boundary sensor went into a fault condition due to the failure of the uninterruptible power supply and the tripping circuit failed to operate.

How did it happen?

Investigation on the first incident found that the designated relay in the gas monitoring controller had not been configured to activate for a failsafe condition. The parameter sheets for the gas monitoring installation stated that the relay should have been configured to activate for a failsafe condition.

The second incident investigation found that another digital address module was still active on the signal line from a redundant gas monitoring station and was transmitting the same address. This prevented the boundary sensor from be able to trip on a fault condition.

Key issues

  • Commissioning and testing plans provided insufficient detail and were not fully completed.
  • Periodic maintenance schedules did not identify the requirement for testing for a failsafe condition.
  • Periodic maintenance schedules did not identify the requirement to verify parameter settings.
  • Verification methods utilised to test all operational tripping functions were not adequate.
  • Decommissioning of redundant gas monitoring installations / stations was not adequate.

Recommendations

Mines should review their safety and health management system to ensure:

  • where gas detectors are used to initiate alarms and/or tripping functions remote to the detector itself. A requirement to test alarms should include verification of the actuation of the remote alarms and tripping functions.
  • periodic maintenance schedules associated with gas monitoring verify parameter settings. 
  • that if a fixed methane detector malfunctions or fails, the fixed methane detector will automatically cause the equipment, or part of the equipment, the detector is monitoring to shut down and give a visible alarm.
  • authorised personnel are deemed competent and have the knowledge, skills and experience to effectively and safely carry out activities associated with gas monitoring systems.
  • that decommissioning of redundant gas monitoring installations / stations is effective.

Investigations are ongoing and further information may be published as it becomes available. The information in this publication is what is known at the time of writing.

We issue Safety Notices to draw attention to the occurrence of a serious incident, raise awareness of risks, and prompt assessment of your existing controls.

References and further information

Authorised by Shaun Dobson - Chief Inspector – Coal

Contact: Mark Lydon, Inspector of Mines (Electrical) , 0436 950 514

Issued by Resources Safety & Health Queensland

Safety: This information is issued to promote safety through experience. It is not to be taken as a statement of law and must not be construed to waive or modify any legal obligation.
Placement: Place this announcement on noticeboards and ensure all relevant people in your organisation receive a copy.