“Overpressure Event” in Goonyella Middle Seam, what does it mean? Why is it the new buzzword? Methane Explosion the Queensland Mining Voldemort. “Thou shall not even say his name”

Overpressure Event has now become a new term trotted out whenever there is a likely methane explosion in the Goonyella Middle Seam.

An overpressure event in an underground coal mine can only be from an Explosion or a massive roof fall.

To get a massive roof fall in a longwall or conventional secondary extraction board and pillar mines requires a “strong” or as it is often termed a “massive” roof structure.

These are usually either conglomerate or sandstone roofs in coal mines.

The Goonyella Middle seam does not contain such structure in the roof layers of the coal seam.

If anything the Goonyella Middle Seam Roof distinctly at the complete opposite end of the spectrum where the roof is not very strong at all.

Like most longwalls in such seams the Longwalls do go through a predictable cyclic loading cycle on average every 15 to 20 metres of retreat.

The only time I am aware of where a true roof fall overpressure event occurs in Goonyella Middle Seam is when the primary roof support installed in gate roads fail catastrophically as in North Goonyella 2Nth from memory in the very early 2000’s.

I have been fortunate that except for usual falls during pulling of pillars I have never experienced such an event in person.

I am however aware of what effect occurs when around 2 hectares of roof fails catastrophically.

Luckily no one was underground at the time but at BOCUM Colliery at Collinsville around the year 1990 approximately two hectares (five acres) of roof failed at once in a partial extraction panel over Xmas New Year.

Due to it being the Xmas holiday period the BOCUM mine was was operating on Dayshift only and the fall occurred in the early hours of the morning so no one was underground or even at the mine when the roof failed.