The biggest danger comes from "unplanned movement", when a piece of machinery such as a continuous miner moves unexpectedly.
Since 1995, in the New South Wales underground coal industry there have been 71 incidents of unplanned movements of remote controlled machines that the NSW Department of Mineral Resources (DMR) is aware of. These have involved breaker line supports (two incidents), longwall shearers (seven), and mobile roof bolters (four). Continuous miners, roadheaders and bolter miners have been involved in the remaining 58 incidents.
According to DMR statistics, 36% of these types of incidents are caused by equipment hardware and 13% by transmitter operator switches. Unknown causes make up 29% of incidents.
In June last year, for instance, a remote controlled roof bolter moved forward unexpectedly when the operator restarted the machine. He had not realised that a switch was stuck in the forward position.
After the June incident, the DMR issued a Safety Alert, recommending various actions, including checking that radio transmitters complied with one of two standards: AS4240: 1994 "Remote controls for mining equipment" or MDG5001: 1998 "Guidelines for the Design of Remote Controlled Mining Equipment".
The DMR has been monitoring the use of radio remote equipment in the industry since 1994. Industry surveys have been conducted and mines have been audited in an effort to reduce the risks associated with the use of remote controlled mining machinery.
Yet, despite DMR recommendations to bring such equipment into compliance with standards, recent DMR surveys found “industry self-assessment indicates that none of the systems are fully compliant with MDG5001 or AS4240,” the DMR said.
The issue came to a head for the industry a few months ago when an unplanned movement took place at a NSW colliery.
The underground mine was operating its remote equipment out of compliance (as is the vast majority of the rest of the industry) but had in place a system whereby transmitters were serviced every 12 months as a way of ensuring safe operation. The transmitter’s failure came only three months after such a service.
Many coal mines had conducted similar risk assessments on their remotely controlled systems to ensure they were being operated safely, albeit in non-compliance.
DMR investigations found that selection of one function only by the operator has resulted in the activation of multiple functions - electric motors and hydraulic circuits initiated continuous miner movement without the operator selecting the particular function.
“The incidents represented a particular recurring fault that should not be so frequent,” the DMR said.
The department issued an alert in early May, recommending as a matter of urgency, the assessment of all radio remote systems.
“Where an assessment identifies that a single electrical fault on the transmitter can cause unintended hazardous motion of the machine, the transmitter should be modified as a matter of urgency…”
The single fault had been identified in tests in radio transmitters that are fitted to many Australian continuous miners, and occurred due to deterioration over an extended period of time.
Under the legislative empowerment entrenched in the legislation (in Clause 51 Coal Mines (General) Regulation 1999), the DMR’s alert was essentially an ultimatum to the industry to get its equipment into compliance.
Those mines that conducted earlier risk assessments and which believed they were operating radio remotes safely had now been informed in no uncertain terms that operating outside the standards, regardless of what safety procedures were in place, was no longer acceptable.
Amazingly, virtually all current radio remote equipment in use in coal mines is out of compliance with the standards. For example, of the 100 odd continuous miners currently operating in underground coal mines in Australia, only two appear to be fully compliant with the standards.