“We installed a timber and brattice seal at the 70m mark in the tunnel and have been pumping nitrogen inside between this and the temporary seal to act as a balance chamber,” he said on Friday.

“Barometric pressure changes will now act on the nitrogen rather than fresh air – we want to minimise oxygen ingress into the mine.”

He said an excavator was used to remove the gravel and shotcrete of the old seal and the two old sea containers were removed.

One of the sea containers was used as a docking station for the GAG inertisation unit and a re-entry block, Ellis said, while the other was part of the seal.

This week the remaining conveyor infrastructure to the seal will be removed and preparations will be made to install the steel air doors.

Under the conceptual re-entry plan, Mine Rescue personnel will set up temporary seals at intervals of 200 to 300 metres.

Fresh air would then be allowed into the mine up to each temporary seal as rescue specialists progressively worked their way up the tunnel.

This exercise would help identify whether the tunnel could be recovered and could allow personnel to get a better idea of how serious the roof fall was at the end of it.

About 1600m into the tunnel is an abandoned load-haul-dump vehicle.

Camera-equipped bomb disposal robots and the Western Australian Water Corporation’s tunnel inspection vehicle have failed to get around the LHD in all attempts so far.

An accompanying photo story is published in today’s newsletter.