Leaked government documents suggest workers for mining company Linc Energy were exposed to “uncontrolled releases” of gas in Queensland.

An internal government briefing document reported on by the ABC appears to show a deep level of concern and investigation coming from Queensland’s environment department.

More than 90 former Linc employees and consultants were interviewed following raids from court-issued search warrants in October 2013.

The internal document says raids were undertaken after the environment department received “information from a number of confidential informants” about incidents at the Chinchilla Underground Coal Gasification (UCG) site dating back to 2007.

Linc Energy already faces criminal charges over allegations of serious environmental harm at Chinchilla.

The plant near Chinchilla, west of Brisbane, produced Syngas (synthetic gas) by burning subterranean coal seams to release gas.

That gas also contains carbon monoxide, benzene, toluene and other toxic or carcinogenic substances.

In the report, a medical expert who reviewed workers' statements and medical records said “the symptoms presented are consistent with exposure to the known chemical constituents of syngas”.

“All of the evidence obtained through warrants and witness statements has confirmed the information from the original informants,” the document states.

The Underground Coal Gasification (UCG) process is hugely controversial.

Pioneered by the Soviet Union, the technique produces gas for power generation by igniting deep coal seams and injecting oxygen so that it will burn.

To do it safely, all gasses must be effectively contained underground.

An independent scientific panel on UCG for the Queensland Government said the Chinchilla site chosen by Linc Energy had unsuitable local geology.

Linc Energy stopped work at the plant in 2013, accusing the former LNP Queensland government of unfairly favouring coal seam gas extraction over UCG.

The company was a major donor to the LNP, giving $100,000 to the Queensland branch of the party in 2012-13 financial year, and $100,000 to the Federal LNP the following year.

It donated smaller amounts to the Queensland and federal branches of the Australian Labor Party as well.

More details are available in this news report.