A floor heave event occurred releasing CH4 gas into working face in MG104. The gas release event caused the Continuous Miner to trip power on the GB gas sensor. A hand held gas detector at the continuous miner recorded peak readings of 1.1% CH4 while the second unit presented an off-scale reading.
A Methane Inrush is a Methane Inrush no matter whether it is referred to as floor-blow incidents or methane floor blowers, or floor blowers in the goaf or floor heave events causing uncontrolled releases of methane or floor lift/gas emission incidents
How any sane person, let alone any Mines Inspector, Underground Mine Manager, SSE or Ventilation Officer can believe that a coal mine that keeps having methane Inrushes in Development and will not struggle in Longwall operations and have multiple methane HPI’s is beyond me.
Especially when the Ventilation at Development working face with both aux fans running was 29m3/sec and off scale (>5% methane) was detected.
The gas release event caused the Continuous Miner to trip power on the GB gas sensor.
A hand held gas detector at the continuous miner recorded peak readings of 1.1% CH4 while the second unit presented an off-scale reading.
It is believed that methane from the seam below has migrated into the stone above but is held in there by minor pockets created by geological disturbances.
HPI’s from Methane Inrushes from the Floor continue to occur in Development in MG 104 after the 9th of May 2018.
There are 5 in Development in MG 104 between the 29/10/18 and 01/12/18
There are also at least 2 documented to have occurred in the LW 102 Goaf prior to the Inspectors MRE of the 9th of May. MRE – Grosvenor Coal Mine – 9.5.2018
Inspector Gouldstone made this comment about MG 104 methane floor blowers and how they appear to have been mitigated in his MRE 6th August 2019 MRE – Grosvenor Coal Mine RG – 06.08.2018.pdf
We also discussed the problems associated with methane floor blowers which, more consistent floor horizon control, appears to have mitigated. The area currently being mined is not in the higher risk zone for floor emissions.
Inspector Gouldstone has also noted the Tonstein band is acting as a cap rock.
There are 5 in Development between the 29/10/18 and 01/12/18
There are also at least 2 documented to have occurred in the LW 102 Goaf prior to the Inspectors MRE of the 9th of May. MRE – Grosvenor Coal Mine – 9.5.2018
These coincided with high loading on LW shields and it is believed that this loading may be as a result of the thickening of overlying sandstone in the roof strata
This is when the Inspectors stated
It was also acknowledged that continued HPl’s with Methane greater than 2.5% was not satisfactory and the mine must ensure that such HPl’s are minimised, and preferably eliminated going forward.
Inspector Gouldstone’s confidence seems ill- placed given his comments in December.
Gouldstone’s concluding statement about methane inrushes is
The matter will continue to receive particular attention and I later talked to officials in the development.
HOW MUCH ATTENTION ARE THE INSPECTORS GOING TO GIVE METHANE INRUSH HPI’s FROM THE FLOOR?
AFTER ALL IN MAY THE INSPECTORS SAY
continued HPl’s with Methane greater than 2.5% was not satisfactory and the mine must ensure that such HPl’s are minimised, and preferably eliminated going forward.
WHICH ONE OF THEIR POWERS WILL THEY USE
MRE – Grosvenor Coal Mine RG Floor blowers – 11.12.2018.pdf
The gas release event caused the Continuous Miner to trip power on the GB gas sensor.
A hand held gas detector at the continuous miner recorded peak readings of 1.1% CH4 while the second unit presented an off-scale reading.
It is believed that methane from the seam below has migrated into the stone above but is held in there by minor pockets created by geological disturbances.
All of the incidents have been involved in the Mine investigation in an attempt to fully understand the circumstances and put controls in place to prevent or diminish the impact.
It is understood that this may take some time and when similar impacts were experienced in MG 102 the drivage was through the problem area before a real solution was effected.
The current area looks at this stage to be associated with the ‘Domains‘. It is believed that methane from the seam below has migrated into the stone above but is held in there by minor pockets created by geological disturbances.
The Mine has now taken the action of drilling proving holes in advance of the drivage to pre-drain the gas and dropped the cutting horizon to remove all coal bottoms. There has been consequential floor control problems following that decision.
Also, even though the cutting horizon effectively removed all floor coal two further incidents were encountered but less gas was emitted, the deduction being that removing all floor coal releases the gas more gradually.
The matter will continue to receive particular attention and I later talked to officials in the development.
I also asked that a copy of the draft investigation report be forwarded as soon as possible so that I could share the detail with fellow inspectors who may have advice on the matter.
LW 104 MG
We were met by two ERZ Controllers at the crib room in MG104 and undertook a long conversation into the succession of floor lift/gas emission incidents that had occurred in the district.
A particular concern was that the decision was taken to not leave any coal bottoms, but still to have two further incidents – albeit of lesser gas volume. The outcome was to introduce other hazards due to the floor breaking up during shuttle car and tramming activity. I understood the concerns but at this stage the priority must be to provide a solution to prevent such events.
We visited the drillers who were commencing a second attempt at drilling a proving/relieving hole. I asked for a copy of the drill plan – the exact direction and inclination detail was still to be received. The underfoot conditions were as had been described and both headings were looking untidy as a result of the change of cutting horizon.
The MRE of the 9th of May
We explained that the mine had reported 32 HPl’s since LW 102 had commenced production in January 2018.
This represented 60% of all HPl’s in Queensland associated with Methane greater than 2.5% in Longwall TG.
I asked what progress the Mine had made since the site meeting that was held with Inspectors and mine management on 16 March 2018.
It was explained that the last two HPl’s appeared to be a result of floor blowers in the goaf. These coincided with high loading on LW shields and it is believed that this loading may be as a result of the thickening of overlying sandstone in the roof strata. Analysis is being undertaken to verify this, The Longwall has approximately 300m to retreat to clear this zone.
We explained that Central Colliery had significant issues with floor blowers and had success by drilling UIS holes into the seam below. These holes did not produce a lot of gas but acted to relieve the pressure so that at times of cyclic loading the floor blowers were effectively eliminated
It was also acknowledged that continued HPl’s with Methane greater than 2.5% was not satisfactory and the mine must ensure that such HPl’s are minimised, and preferably eliminated going forward.
Development MG 104 24 C/T
Mr Niehaus has previously reported the following incident –
An incident occurred in MG104 Development Panel on the 1st of December at approximately 2:28pm. The Continuous Miner was producing in B Hdg 23-24ct and was approximately 66m from the last open cut through.
A floor heave event occurred releasing CH4 gas into working face in MG104. The gas release event caused the Continuous Miner to trip power on the GB gas sensor.
A hand held gas detector at the continuous miner recorded peak readings of 1.1% CH4 while the second unit presented an off-scale reading.
This was one of 5 similar incidents since 29/10/18 shown below*.
01/12/18 Floor gas release 104MG B heading, 23/1 1/18 Floor gas release 104MG 24CT, 09/1 1/18 Floor gas release 104MG B Heading 23CT, 03/1 1/18 Floor gas release 104MG B Heading, 29/10/18 Floor gas release 104MG B Heading 22/23CT*
Gouldstone 6th August 2019 MRE – Grosvenor Coal Mine RG – 06.08.2018.pdf
MRE – Grosvenor Coal Mine RG Floor blowers – 11.12.2018.pdf
2.3 Longwall 104MG 17 CT
We also discussed the problems associated with methane floor blowers which, more consistent floor horizon control, appears to have mitigated. The area currently being mined is not in the higher risk zone for floor emissions.
MRE – Grosvenor Coal Mine RG Floor blowers – 11.12.2018.pdf
Development MG 104 24 C/T
Mr Niehaus has previously reported the following incident –
An incident occurred in MG104 Development Panel on the 1st of December at approximately 2:28pm. The Continuous Miner was producing in B Hdg 23-24ct and was approximately 66m from the last open cut through.
A floor heave event occurred releasing CH4 gas into working face in MG104. The gas release event caused the Continuous Miner to trip power on the GB gas sensor.
A hand held gas detector at the continuous miner recorded peak readings of 1.1% CH4 while the second unit presented an off-scale reading.
The outbye general body gas sensor at the dogleg read a peak of 0.34% CH4. Ventilation at working face with both auxiliary fans running was 29m3sec.
This was one of 5 similar incidents since 29/10/18 shown below*.
All of the incidents have been involved in the Mine investigation in an attempt to fully understand the circumstances and put controls in place to prevent or diminish the impact.
It is understood that this may take some time and when similar impacts were experienced in MG 102 the drivage was through the problem area before a real solution was effected.
The current area looks at this stage to be associated with the ‘Domains‘. It is believed that methane from the seam below has migrated into the stone above but is held in there by minor pockets created by geological disturbances.
The Mine has now taken the action of drilling proving holes in advance of the drivage to pre-drain the gas and dropped the cutting horizon to remove all coal bottoms. There has been consequential floor control problems following that decision.
Also, even though the cutting horizon effectively removed all floor coal two further incidents were encountered but less gas was emitted, the deduction being that removing all floor coal releases the gas more gradually.
The matter will continue to receive particular attention and I later talked to officials in the development.
I also asked that a copy of the draft investigation report be forwarded as soon as possible so that I could share the detail with fellow inspectors who may have advice on the matter.
LW 104 MG
We were met by two ERZ Controllers at the crib room in MG104 and undertook a long conversation into the succession of floor lift/gas emission incidents that had occurred in the district.
A particular concern was that the decision was taken to not leave any coal bottoms, but still to have two further incidents – albeit of lesser gas volume. The outcome was to introduce other hazards due to the floor breaking up during shuttle car and tramming activity. I understood the concerns but at this stage the priority must be to provide a solution to prevent such events.
We visited the drillers who were commencing a second attempt at drilling a proving/relieving hole. I asked for a copy of the drill plan – the exact direction and inclination detail was still to be received. The underfoot conditions were as had been described and both headings were looking untidy as a result of the change of cutting horizon.
