Safety concerns were raised with the state-owned operator of a Central Queensland power station years before a catastrophic explosion led to major blackouts across the state, a damning report has revealed.

The Callide C power station explosion in 2021 led to almost half a million Queensland customers losing power — the worst outage in decades.

A report by forensic engineer Dr Sean Brady, which was released on Wednesday, found operator CS Energy had "substantive and longstanding issues" with safety.

"The failure to implement effective process safety practices was not unique to the incident" on May 25, 2021, he noted.

"Rather, it was consistent with an organisation that did not value or practice effective process safety."

In February 2019, a CS Energy employee discussed in their exit interview what they alleged was an "unsafe work environment", the report said.

"The lack of maintenance at Callide over the last few years, pushing out overhaul dates, ageing plant and budget restrictions, four fires in five months and several managers over the past few years is a concern," the employee said, according to their meeting notes, which were included in the report.

The employee said during their exit interview that they "did not wish to be alarmist", but that "these items together are the telltale signs that a process safety incident is quite possible".

A short time later another safety specialist resigned, and while these roles looked to be backfilled, "there was effectively no process safety team from April 2019 to July 2020", the report said.

Communication between the Queensland government and CS Energy on the day of explosion has revealed the immediate response to the crisis.

"Hope the CS team are okay. We are triaging the whole energy sector issues and the following are best answered by CS Energy," a government email to the company on the night of the incident reads.

It goes on to ask about maintenance at the site and the process of an investigation into the incident.