Published in March 2008 Australian Longwall Magazine

Among the most vulnerable to electrical failure and increased danger are the workhorses of the underground mining process – continuous miners and shuttle cars.

John Waudby, senior inspector of electrical engineering for mine safety operations with the New South Wales Department of Primary Industries, told Australian Longwall most of the damage sustained to these machines was through either impacts or a build-up of debris.

While he said this sort of damage was not likely to cause an operator to be shocked, it did increase the possibility of exposed electrical arcing occurring, in turn raising the possibility of igniting any methane that might be present.

“Generally speaking, there is no electrical shock hazard associated with these machines – this is all about having equipment that is not going to ignite an explosive atmosphere of methane,” Waudby told AL. “That’s why we like to look at what’s happening with the failure of explosion-protective properties of electrical equipment.

“The other one is cable arcing in a hazardous zone,” he said. “There have been instances where people have received burns and electric shocks, but it’s more about arcing, and if there’s methane there’s a good chance it’ll explode.

“The well-known issues with shuttle cars are cable reels not functioning properly, incorrect anchoring, back spooling and things like that. Cable handling mechanisms are a significant causal factor, and then operator error is high on the list as well.”

Surprisingly, Waudby said the number of arcing incidents – in New South Wales at least – has actually increased substantially over the last 20 years.

“In 1985 to 1986, we had 1.3 arcing incidents on shuttle cars per million tonnes of coal moved by shuttle car, and in 2006 to 2007, we had 7.5 incidents per million tonnes of coal moved by shuttle car,” he said.

“All the techniques that were required for preventing shuttle car cable arcing were well known back in the 1980s – yet consistently, those things aren’t being applied by the mines. But in that time there’s been a move away from bord and pillar to longwall mining, and so we move proportionally less coal now with shuttle cars than we did then.”

Waudby said there has also been another significant change within the industry over that time which has probably affected those figures.

“Generally speaking, the responsibility for actually making sure that cable management systems are functioning properly is starting to be dispersed now, as they have management structures that are process oriented,” he said.

“So there’ll be someone responsible for the management of development and someone responsible for longwall production. Whereas before, all that responsibility for cable management was vested in the mine’s electrical engineer. So maybe there is not the same focus as there once was.

“Our strategy is that the people responsible are held to account. So while the manager of electrical engineering might set the standard, our questions will be to the production manager – the person who’s actually responsible for the day-to-day operations.”

While electrical arcing is the primary safety issue in underground coal mining, Waudby said electric shock risk is still one which requires careful management.

He said that from 1999 to 2007, 80% of electric shock incidents were due to electrical equipment not being fit for purpose, although he said this figure is also derived from incidents occurring at surface metalliferous mines and in processing plants.

But he said the issues – such as equipment selection and maintenance – were still applicable to underground coal mines.

“And the fact is that 75 percent of electric shocks are not to electrical workers. They’re to people touching a piece of equipment to do a normal job, expecting the piece of equipment to work properly,” Waudby said.

“The biggest gains would be made if the equipment was selected and maintained properly – we’d be able to drive down the number of electric shocks significantly.”

“In 1985 to 1986, we had 1.3 arcing incidents on shuttle cars per million tonnes of coal moved by shuttle car, and in 2006 to 2007, we had 7.5 incidents per million tonnes of coal moved by shuttle car.”