The incident occurred when a longwall tailgate goaf seal, located about 1300m from the working face, collapsed. It was believed a windblast from a relatively small fall of roof behind the retreating face-line blew the seal.

If not properly sealed, oxygen could enter a goaf causing an explosive mixture to form with potential hazards for workers such as exposure to noxious and explosive gases.

On inspection it was found the construction of the failed ventilation control device was from 50-150mm thick, well below the 300mm design thickness required by the design documentation for a Type C Seal.

“All VCDs in Queensland underground coal mines are to be constructed/installed to the design specifications, as required to ensure that the VCD complies with the design criteria and the requirements of the Coal Mining Safety and Health Regulation 2001, Schedule 4 - Ventilation control devices and design criteria,” the NRM said.

It warned mine managers to ensure they understood the VCD test and design criteria required to substantiate the VCD rating.

“This requires an assessment of the structure design and performance capability of the VCD itself, as well as the performance characteristics of the peripheral interface between the VCD and the strata,” NRM said.

Mines were advised to make sure inspection and auditing procedures were in place for specifying and constructing VCDs. Further, mines were required to develop a test and check regime to check that “as built” VCDs had been constructed in accordance with the design.