Now, as a result of a government department safety alert, equipment suppliers are busily developing shutdown solutions; and mines are fitting temporary measures to manually shutdown all diesel engine systems in an emergency.

Following the event, Rob Regan, chief inspector of coal mines at the NSW Department of Primary Industries issued a safety alert recommending suppliers and mines fit an emergency manual shutdown system until a more engineered solution was developed.

Mines inspectors in both NSW and Queensland stressed mine operators should be more diligent in managing a mine atmosphere while acknowledging the event was very rare.

It is understood exactly what happened though it appears for the engine to have run largely on methane took the synchronous line-up of several circumstances that would not usually occur.

The event happened when a deputy at the mine drove a man transport vehicle into the mine’s longwall return headings. This was after he had checked and diluted methane levels from 2.5% to 0.7%.

At roughly the same time, an inrush of methane from the longwall goaf flooded the heading due to a damaged seal and change in ventilation. So instead of driving into what he thought was a fresh air intake, he was actually entering a methane-rich environment.

As he drove inbye, the methane detector went off indicating a methane concentration of greater than 1% - other later readings confirmed methane had been at least 8%. As the air source became enriched with methane, the diesel engine started revving high.

The deputy tried frantically to turn the machine off, but the diesel engine was uncontrollable for some period of time. The diesel engine only stopped of its own accord when the ventilation returned to normal. The vehicle had meanwhile become so hot the epoxy paint on the exhaust manifold turned to ash.

This occurred because methane burns at roughly twice the temperature of diesel and will most probably overheat, with potentially catastrophic consequences.

Subsequent investigations by the Department of Primary Industries suggested for a diesel engine to run primarily on methane the engine had to be hot and operating under load in a methane-rich atmosphere of greater than 5%.

“Strictly speaking, a diesel engine cannot run on pure methane under normal conditions. It is believed an initial ignition source is required which can come from a range of sources,” said senior inspector of mechanical engineering NSW, Gordon Jervis.

But investigators are unclear about the ignition source in this instance. A DPI simulation after the event showed the vehicle had been shut down by normal methods yet continued to run and inspectors have indicated further research is required to understand the source of the ignition.

Furthermore, the engine system appeared to be clean and there was no evidence of oils, grease or coal dust on the hot exhaust manifold. In fact, it is thought the cleanliness of the engine may have been one of the saving factors in preventing a methane explosion.

Some equipment manufacturers doubt the vehicle ran on methane alone. They feel there had to have been some diesel present to fuel the engine, but until further research is undertaken this information is not available.

To meet the NSW departmental recommendations OEMs are devising an array of solutions. VAMT, manufacturer of the Eimco equipment range, already have an automatic shutdown valve on gear that is operating in Norway but it wouldn’t fully comply with the Australian guidelines. VAMT is also examining a second option of a manually operated inert gas shutdown.

DBT Diesel has proposed an intake shutdown butterfly. DBT equipment also comes with a methane shutdown option.

Similarly, PJ Berriman has developed a strangler valve that removes air supply in an emergency. Managing director Phil Berriman believes the strangler valve the best solution and he said his company had tested and fitted its third valve to date.

As Berriman said, while the probability of such an incident happening is low, the consequences are very high, which makes finding a solution so imperative.

The Queensland Department of Natural Resources and Mines is keeping a close watch on what happens. Acting deputy chief inspector of mines (technical), David Mackie, said under Queensland legislation OEM’s had to examine the event and decide what action to recommend to mines and contractors that use their equipment.

Mackie is also chairman of Australian Standard AS 3584 governing explosion-protected diesel engines systems operating in underground mines. He expects to reconvene the Australian Standards meeting to implement possible changes to the standard in the light of the event.

“We would prefer to put forward guidelines that are enabling rather than specific,” Mackie said.

Jervis said under NSW legislation because the phenomenon had occurred and the risk was now known, the industry had a responsibility to put in place engineered solutions to preclude this happening again.