The NSW Department of Planning and Environment’s Resources Regulator has slapped South32 with a prohibition notice after it failed to immediately withdraw workers from the mine during last week’s incident. 

Underground operations have ceased, pending a detailed investigation into the failure and adequate safety measures being put in place.

The prohibition notice – which bans all workers from entering the site’s underground workings, except for those undertaking safety-related activities – was issued following a failure of the mine’s surface gas drainage plant on January 8.

“The operation of the gas drainage plant is essential in maintaining gas at safe levels in the underground workings,” a NSW Resources Regulator spokesman said.

“Subsequent investigation by the regulator identified that the mine failed to follow its trigger action response plan for withdrawing workers after the gas drainage plant stoppage.

“The mine’s trigger action response plan requires that workers are immediately withdrawn from the mine in such instances.”

The spokesman said the notice would remain in place until a detailed investigation into the cause and circumstances of the incident was completed.

The regulator would have to be satisfied controls were in place, “to ensure workers ... are not exposed to risk”, before the ban was lifted, he said.

A South32 spokesman said the company withdrew the mine’s workforce following the “disruption to its gas extraction system”.

“The safety of our people always comes first,” he said.

“At no time were there elevated levels of gas underground or concerns with the mine’s ventilation system.”

The spokesman said the NSW Department of Planning and Environment was notified and subsequently issued the prohibition notice.

“Underground operations at our Appin mine are currently suspended while we work with the regulator to address these concerns,” he said.

The latest Appin mine incident was the fifth investigated by the NSW Resources Regulator since late 2016.

In August, miners resumed underground work after a seven-week shutdown due to gas and ventilation issues.

In May, elevated gas levels saw a prohibition notice issued and strict safety controls enforced by the regulator.

In October 2016, underground operations ceased after a dangerously-high level of methane was detected.

South32 has commissioned an independent review of its gas drainage and ventilation, as well as its critical equipment reliability, the company’s spokesman said.