The operator did not become aware of the loss until he reached the surface at the end of his shift, at which time he attempted to contact the production area where he had been working in the Hunter Valley.

An unsuccessful search was conducted for the unit and operations resumed as normal.

The device was eventually found when it was ejected from the rear of the left-hand side track of a roadheader, totally destroyed, and a fire was observed at that time.

The operator had been involved in various tasks during his shift. The device was being belt worn, constrained by a webbing-style pouch that was supplied by the manufacturer of the units.

An investigative report from the US Department of the Interior - Bureau of Mines confirms that these units can be subject to “combustion reactions” when placed in extreme destructive forces, such as those applied by a rotating track pad.

The mine concerned conducted a range of tests and under certain conditions was able to remove a rescuer from its retaining pouch, with the restraining strap still secured.

“The possibility of this event occurring should be communicated to all people required to wear such a device during their duties,” the inspectorate recommended.

“Operations should review the adequacy of their arrangements for finding self-contained self-rescuers if lost, with the potential for such an end result as occurred in this case to be considered.”