The NSW Resources Regulator recently issued a safety bulletin following three incidents which have occurred recently at longwall mines in which rapid face bolters have disengaged from the armoured face conveyor (AFC) rack bars.
All three incidents involved rapid face bolters that had been hired by the mine operator. In the first incident, a rapid face bolter was tramming across a face. When it stopped, a spotter noticed that the trapping shoe was sitting 100 millimetres forward of the AFC rack bars. The rigs were not retracted while tramming.
In the second incident, towards the end of a shift, a worker had completed installing a roof bolt and trammed the rapid face bolter about 300 millimetres. A monitoring hole was then drilled.
The worker was leaving the bolter when he “noticed that the tailgate side trapping shoe was not engaged with the AFC rack bar.
In the third incident, a rapid face bolter was positioned on an AFC near the tailgate drive. The operator extended the platforms and positioned the rigs, then identified the bolter was in the wrong location. The bolter was then trammed towards the main gate when it unexpectedly stopped.
The worker assumed it was jammed and reversed towards the tailgate, freeing the bolter. The worker then started tramming the bolter towards the main gate. The bolter then disengaged from the AFC rack bar and tipped 45 degrees towards the face.
The worker was ejected off the bolter, landing in front of the bolter between the two drill rigs. The worker suffered minor injuries requiring first aid treatment on site.
An investigation identified that when the rigs and platforms were extended, the centre of gravity shifted close to the skid shoe. As the rack bar position moved on the ramp pans, this shifted the bolter forward, tipping the bolter.
The safety bulletin subsequently made a number of recommendations:
1. Conduct an engineering review of the compatibility with the panline, rack bar and rapid face bolter. Ensure the trapping shoe engagement is sufficient to retain the bolter in all foreseeable operating configurations.
2. Verify that rack bar engagement with the trapping shoe is sufficient to retain the bolter as part of commissioning checks. 3. Repeat the above checks for any non-standard sections of the panline such as transitions and ramp pans.
4. Update operating procedures and training material to require that rigs are parked and platforms are retracted as specified in the original equipment manufacturer (OEM) requirements when rapid face bolters are trammed.