The inquiry detailed the cause, reaction, internal reporting and risk mitigation of 13 high risk methane exceedances across three mines, Oaky North, Moranbah North, and Grasstree.
The inquiry detailed the cause, reaction, internal reporting and risk mitigation of 13 high risk methane exceedances across three mines, Oaky North, Moranbah North, and Grasstree.

IN DEPTH: 13 mining incidents failed to reach management

Multiple reports of dangerous gas exceedances deep underground were not passed up to senior mining executives, the Queensland Coal Mining Board of Inquiry has found.

The board's first part of the inquiry report, which was released on Thursday, focused on the initial tranche of public hearings held in August.

The inquiry detailed the cause, reaction, internal reporting and risk mitigation of 13 high risk methane exceedances across three mines, Oaky North, Moranbah North, and Grasstree.

"The combined controls of ventilation and gas drainage did not deliver the desired outcome in terms of keeping methane concentration below prescribed levels," the inquiry said.

The inquiry found that none of the high potential incidents were classified by the mine operator or relevant parent company as a high potential incident for internal investigation and reporting.

"(And) none of the high potential incidents … were viewed by the mines' investigation teams as involving a failure of a critical control," it said.

Anglo American metallurgical coal CEO Tyler Mitchelson arrives at the Brisbane Magistrates Court to give evidence to Queensland's coal mining board of inquiry, investigating dangerous methane levels at Anglo's coal mines on August 17 2020. Picture: Glenn Hunt
Anglo American metallurgical coal CEO Tyler Mitchelson arrives at the Brisbane Magistrates Court to give evidence to Queensland's coal mining board of inquiry, investigating dangerous methane levels at Anglo's coal mines on August 17 2020. Picture: Glenn Hunt

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However Anglo American incidents were classified as Department of Natural Resources and Mines high potential incidents.

"In Anglo's case, there was no formal, documented process by which methane exceedances

under the legislation were notified as soon as possible to the most senior executives of the

parent companies," it said.

A methane exceedence at Moranbah North in July 2019 was not reported as an internal high potential incident despite "gas concentration as 'tailgail off scale'".

"This methane exceedence may have risen to a point within the explosive range in the tailgate area," the inquiry said.

A cluster of eight methane exceedances at Grasstree mine was blamed on a poorly placed sensor and localised layering of the gas.

However the inquiry said there was an "unacceptable delay" in addressing the incident.

"There was unacceptable delay in mine management successfully communicating to workers the proper sequence of shield advance," it said.

"This in turn contributed to the delay in addressing the exceedances."

Workers protested near Anglo American's Moranbah North Mine over safety concerns on Friday June 5 2020.
Workers protested near Anglo American's Moranbah North Mine over safety concerns on Friday June 5 2020.

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The inquiry has recommended the mine operators and parent companies classify all methane exceedances at or above 2.5 per cent as a high potential incident for reporting purposes.

It said the companies should treat the methane exceedances as indicating a critical control may have failed, and undertake an investigation into the incident.

 

"Of course, the implementation of recommendations takes time," it said.

"It is hoped that, in the interests of safety, accepted recommendations will be acted upon without delay."

How each high profile incident occurred:

Provided by the Queensland Coal Mining Board of Inquiry

Oaky North

Oaky North underground mine is in Queensland's Bowen Basin about 90 km northwest of Emerald.
Oaky North underground mine is in Queensland's Bowen Basin about 90 km northwest of Emerald.

Glencore Oaky North is part of the Oaky Creek Coal complex. It is located in the Bowen Basin, about 90km northwest of Emerald.

As at December 2019, it had a labour force of 450 workers, comprised of 290 employees and 160 contractors.

December 6 2019: The high potential incident was caused by the shearer cutting into a blockside stub, which affected ventilation flow at that point, allowing the goaf stream to move forward onto the face.

This incident was unexpected.

While the location of the stub was known in advance, there had been two prior instances of mining through a blockside stub on the same longwall block without causing an exceedence.

The event resulted from the failure to install a brattice curtain, a temporary ventilation device consisting of a woven antistatic and fire-resistant propylene cloth that is hung from the roof to redirect airflow.

The event was not indicative of a failure of the overall ventilation system.

Once the incident occurred, it was appropriately managed by a number of measures.

The explosion risk zone controller attended promptly and commenced appropriate rectification to reduce the methane level within a short time.

The ventilation officer circulated relevant data to the site senior executive, underground mine manager and others by email.

The underground mine manager, who was absent at the time, returned to the mine to assess the situation and implement further controls.

Moranbah North Mine

Anglo American’s Moranbah North is located 16 km north of the Moranbah township, and approximately 220 kilometres southwest of Mackay.
Anglo American’s Moranbah North is located 16 km north of the Moranbah township, and approximately 220 kilometres southwest of Mackay.

Anglo American's Moranbah North is located 16km north of the Moranbah township, and approximately 220km southwest of Mackay.

It adjoins Grosvenor mine.

As at May 2020, it had a labour force of 1193 workers, made up of 435 employees and 758 contractors.

July 20 2019: Five operators were at the face at the time.

The cause of the high potential incident was floor heave and floor breaks, allowing methane to be released from the Goonyella Middle Lower seam, which was only 20-30cm below the mined area.

Contributing factors were insufficient pre-drainage of the Goonyella Middle Lower seam, and that the most proximate gas drainage borehole was in standby mode at the time.

The issue was immediately managed by redirection of ventilation using brattice sails to

dilute the methane.

On the evidence of the Control Room Operator's email, which noted gas concentration as 'tailgate off scale', this methane exceedence may have risen to a point within the explosive range in the tailgate area.

Moranbah North management did not classify the methane exceedence as an Anglo high potential incident for internal reporting purposes.

The gas drainage critical control failed as a result of the inadequate drainage of the Goonyella Middle Lower seam.

This incident was not indicated on the learning from incidents report as a failure of a critical control.

With a view to minimising risk of recurrence, engineering controls were adopted to ensure adequate drainage of the Goonyella Middle Lower seam.

The investigation and subsequent corrective actions are a good example of learning from the experience of a high potential incident and putting in place engineering controls to prevent recurrence.

Grasstree Mine

Grasstree mine is located approximately 37 kilometres southwest of Middlemount and 120 kilometres northwest of Emerald in the Bowen Basin.
Grasstree mine is located approximately 37 kilometres southwest of Middlemount and 120 kilometres northwest of Emerald in the Bowen Basin.

Grasstree is located approximately 37km southwest of Middlemount and 120km northwest of Emerald in the Bowen Basin.

Together with Capcoal Open Cut Mine, it forms the Capcoal complex.

As at May 2020, it had a labour force of 782 workers, made up of 431 employees and 351 contractors.

July 28 2019:

The first incident involved a peak methane reading of 2.98 per cent. The Learning from Incidents report said there was steadily rising gas levels at the tailgate through the day, culminating in an exceedence from 1.15pm.

The cause of the exceedence was goaf drainage plant failure, due to a burst radiator hose on a compressor, at a time when the goaf drainage system was operating at full capacity.

Although the immediate issue of a failed radiator hose was able to be rectified after some hours of lost production, the bigger issue was inadequate goaf drainage.

It was plainly unacceptable from a safety and production perspective for the goaf drainage system, fundamental to safe mining, to fail for want of a radiator hose.

The corrective measures to increase goaf drainage capacity were effective in preventing

further recurrences.

Grasstree management did not classify the methane exceedence as an Anglo high potential incident for internal reporting purposes.

The gas drainage critical control failed as a result of the plant failure when the goaf drainage system was operating at full capacity.

This incident was not indicated on the Learning from Incidents report as a failure of a critical control.

The investigation and subsequent corrective actions are a good example of learning from

the experience of an high potential incident and putting in place engineering controls to prevent recurrence.

October 25 2019:

The high potential incident occurred at longwall 808 a few days after production commenced on that longwall.

At 6.05pm the shearer stopped and latched due to methane concentration being greater than 1.9 per cent at the tailgate roadway sensor.

The cause of this high potential incident was a ventilation stopping was left in place in an inbye cut-through that connected the C heading to the goaf.

The stopping prevented methane from being drawn from the goaf into the C heading.

Instead, the methane reported to the tailgate area of the longwall face and was drawn down the A heading.

This resulted in a methane exceedence in the tailgate area adjacent to the longwall face.

The immediate remedy was to run a brattice wing to enable additional air to be pushed up

the tailgate roadway.

Subsequent to this incident, the permanent stoppings in the inbye cut-through were

replaced with brattices on retreat, so that the intended ventilation circuit was achieved.

Grasstree management did not classify the methane exceedence as an Anglo high potential incident for internal reporting purposes.

The ventilation critical control failed because the designed ventilation arrangement for clearing gas from the tailgate was not implemented.

This incident was not indicated on the Learning from Incidents report as a failure of a critical control.

January 11 2020:

Involved an exceedence of four minutes' duration, peaking at 3.6 per cent.

The high potential incident was caused by the shearer cutting into a blockside stub which affected ventilation flow in that area.

This event, coupled with a goaf fall, allowed the goaf gases to be pushed over the tailgate drive sensor.

The immediate action taken was to run a brattice wing into the drill stub to direct the air up

the tailgate roadway.

The standardised ventilation arrangement should have been in place before commencing

cutting into the stub.

However, once cutting into the stub commenced, it was a legitimate choice to continue advancing the face to control ground conditions.

The event resulted from the failure to install a brattice curtain.

The event was not indicative of a failure of the overall ventilation system.

Grasstree management did not classify the methane exceedence as an Anglo high potential incident for internal reporting purposes.

February 22 2020 - April 11 2020:

A cluster of eight high potential incidents occurred between February 22 and April 11, 2020. Each of them concerned methane readings of greater than 2.5 per cent recorded on only one

sensor.

Given that location, and the elevated position of the sensor under the canopy, it was soon discovered that there was a high likelihood of its picking up localised layering of methane. This was apparently not foreseen in the choice of location for the sensor.

Although there was a variety of contributing causes, this sensor recorded the cluster of eight exceedances occurring between February 22 and April 11, 2020.

Five occurred between March 20 and 25, with three on March 20 alone.

No other sensor recorded any of those exceedances.

Irrespective of whether it was general body concentration or layering, the regulation requires that the ventilation system must provide for minimising, within acceptable limits, layering of flammable gas.

No doubt this requirement exists because ignition of a methane layer may provide a pathway for a flame to propagate to a larger adjacent explosive concentration of methane, in this case, the goaf.

A uniform system of shield advance was in fact developed, however, it took some substantial time for it to be implemented.

There was unacceptable delay in mine management successfully communicating to workers the proper sequence of shield advance.

This in turn contributed to the delay in addressing the exceedances.

Grasstree management did not classify any of these eight methane exceedances as an

Anglo high potential incident for internal reporting purposes.

In accordance with the system at the time, the cluster of high potential incidents that occurred at Grasstree, involving the sensor, was distributed among several inspectors rather than managed as a group.

The proposed central assessment unit can be expected to ensure a systematic response to such a scenario in future.