Methane Exceedances Mine Record Entry 15th May 2019

On 15 Jun 2019, at 7:53 am, one of the Mines Inspectors wrote to the Site Senior Executive Mr Trent Griffiths about Methane Exceedances in the Tailgate of the Longwall and actions to reduce the risk of greater than 2.5% CH4 occurring.

The Inspector notes that “a number of other exceedances that have recently occurred involved cavities spalling material causing significant ventilation restrictions and changes”

He asks a number of specific questions of Mr Griffths as the SSE

Mr Griffiths initial reply at 8:01 am the same day (8 minutes later)

“Some great questions, appreciate the feedback.

Will send through response next week.”

Reports indicate that on the 6th May 2020 similar issues with cavities in the Tailagte existed immediately prior to the Methane Explosion.

How often does this situation occur in the 12 months between the Mine Record Entry by the Inspector and the Methane Ignition?

What was in the reply to the Mine Record Entry?

Were any actions proposed to address continuing methane excedances?

If so were these Actions put in operation and were they effective?

The Correspondence from the Inspector and the initial Reply by Mr Griffiths are set out below

 

Thank you Trent, acknowledging receiving your form 1A.

Setting aside a number of other exceedances that have recently involved cavities spalling material causing significant ventilation restrictions and changes, taking a closer look at this exceedance are you satisfied your thresholds (trigger points) are set to the correct levels?

I understand they have worked as intended however you have still had an exceedance and the flow on effect being downtime (1.5hrs) waiting for it to reduce to below 2%.

I am not saying you should be slowing the shearer speed over the whole cut cycle (in this case would make no difference) but should you consider reducing the trigger points to avoid reaching the 2.5% and therefore reducing your exposure to this risk and potential downtime.

What if the shearer slow function activated below 2.0%, I’m not going to suggest a value but if it activated earlier would it prevent some of your exceedances?

Are your triggers linked to a falling barometer?

Have you adapted your cut rate to suit the Diurnal periods?

Is your reduced shearer speed with the current trigger points still too quick?

Extract from form 1A

The CH4 shearer slow function worked as intended and slowed the shearer from 2:37pm at

57 roof support when the inbye shearer CH4 sensor located at CH1900 (Face at CH1970 at

time of event) reached 2.0%.

The CH4 shearer halt function worked as intended and stopped the shearer at 2:52pm at 113

roof support when the inbye shearer CH4 sensor located at CH1900 (Face at CH1970 at

time of event) reached 2.2%.

Production recommenced after gaining permission at 4:30pm 12/6/19 and CH4 levels

stabilised below 2%.

 

If you don’t believe it would make any difference with any changes to your trigger points or reduced shearer speed and you would still have the same exceedance and downtime, what work is being done to increase your goaf drainage?

I understand Grasstree is pulling in excess of 14000lt/sec and still having to slow the shearer at times. I do understand there is also a balance to consider with increasing your risk of spon com by increasing your goaf drainage but on a falling barometer and shearer heading toward the TG goaf fringe is overtaking you.

Within the next couple of weeks, can you provide me with a response as to what is the strategy going forward to reduce your exposure to exceedances at Grosvenor please. Please CC in Regional Inspector Peter Herbert into this response.

Regards

Paul Brown

Inspector of Mines

Mines Inspectorate | Resources Safety and Health

Department of Natural Resources, Mines and Energy

 

Paul Brown

Inspector of Mines

Paul,

Some great questions, appreciate the feedback.

Will send through response next week.

Regards,

Trent Griffiths

Site Senior Executive

General Manager