Case Study

On 24 July 1991, three mine workers were asphyxiated by carbon dioxide gas from an outburst at the coalface at South Bulli Colliery near Wollongong, NSW.

Following the routine installation of roof supports, the crew had restarted the cutting of coal. The outburst occurred shortly after, on a reverse thrust fault, previously undetected despite in-seam seismic exploration of the area. Poor roof conditions were observed in the area at the time.

The gas expelled was mostly comprised of carbon dioxide with some methane. The investigation report estimated 6000m3 of gas and 130 tonnes of material was expelled. The outburst was described by the underground workers as being similar to an explosion. They heard rumbling noises, a loud bang, followed by a small percussion wave, which blew open the return ventilation doors.

Workers close to the scene were exposed to dust and gas. They retreated as the asphyxiating effects of carbon dioxide were beginning to affect them. Efforts to access the area were hampered by the carbon dioxide gas. The bodies of two victims were retrieved by mine workers, without the use of rescue suits. A third worker was retrieved by a rescue team, after removing coal from an engulfed continuous miner.

Although Illawarra Bottom Gas (carbon dioxide and methane common in the Bulli coal seam) had been detected in the development of this panel, no gas had been detected during the shift in which the outburst occurred, nor during the previous six shifts.

When gas had been detected previously, it had been treated as a ventilation issue, not as a precursor to an outburst.

The investigation report indicated that there had been five previous low-intensity methane outbursts at the mine. The report also found that survey work completed by the company that owned the site had not been shared with mine management.

The investigation report identified that an outburst management plan had been developed, however, it had not been properly implemented and the quality of the mine’s outburst plan was poor. Training of workers in observing indicators forewarning of an outburst was not done. The preparedness of the mine to rescue workers after an outburst was poorly coordinated. There were repeated failed rescue attempts without proper equipment, putting people’s lives at risk.

In response to the incident, working groups developed MDG 1004 on outburst management, and legislation now requires an outburst principle hazard management plan to be in place at outburst-prone underground coal mines.

This incident claimed the lives of 3 people: Craig Broughton (28), Robert Coltman (43) and Leigh Pearce (24).