A decision was made to re-enter the mine after its CO levels fell from about 6000 parts per million to below 1350ppm earlier this month, bringing it close to the 1200ppm level considered safe.

“It is not really correct to be alluding to any level of CO being a safe level as it depends on the presence of other gases that would determine the safety of the environment and not just CO,” Rowland told ILN.

“The 1200ppm is a Trigger Action Response Plan (TARP) level that was selected for a particular TARP response action to be signalled at.”

High concentrations of CO made it prohibitive to re-enter the Pike River mine until now, when a seal around the metal container, which has acted as a portal into the mine, was removed.

At about 100 metres in mines rescue staff installed a monitoring point to monitor the mine gases remotely and build a temporary seal, a spokesperson for receiver PricewaterhouseCoopers said.

The expert panel has been selected to oversee or “watchdog” all such activities at the mine, Rowland told ILN.

“This group has been established to ensure that external eyes are focused on activities to try and ensure due and safe process,” he said.

“There are six of us on the panel with varying expertise in ventilation, strata, safety, chemistry, and environment.

“The Department of Labour and the NZ mines rescue are not actually a part of, nor do they have people on this group.”

The nearby Spring Creek mine owned by Solid Energy is taking a thorough approach to gas management.

It uses a combination of real time and tube bundle gas monitoring systems to ensure a comprehensive knowledge of the mine environment.

The mine also utilises the gas chromatograph available at the Mines Rescue Station to analyse gas samples.

Some monitors are interlocked with electrical equipment and other monitors are used to activate compressed air operated dilution louver doors.

These doors are used to ensure gas levels remain below critical levels (1.25%) in the return roadways. This helps to reduce electrical interlock trips on the conveyors.

A sample of the gas monitors was selected by the auditors to determine the currency of the calibration of the instruments.

The mine was able to show that these instruments were entered into the maintenance work order system and that they were compliant.

A Ventilation Management Plan for Gas detection systems exists. The setting of gas monitor trip levels and alarms are determined by legislation and through the site TARPs.

The mine uses real time anemometers and this allows the CO make calculations to be automatically calculated.

A mine plan was available showing all gas monitoring locations. Handheld instruments are available to all statutory officials and mine workers operating diesel equipment.

Queensland legislation requires diesel equipment to be fitted with interlocking gas monitors. This is not a requirement of the ASNZ standards.