Fiskville's fire foams still toxic?

Toxic firefighting foams used to contaminate Victoria's Fiskville training centre have been replaced but experts say the new foams could be just as dangerous.

The toxic PFOS-heavy foams have been phased out. But it seems the new foams have the potential to create that same chemical once they interact with the environment.

The Country Fire Authority's Fiskville training centre was permanently closed in March after the discovery of dangerous chemicals in the water and a cancer cluster among those linked to the site.

Nigel Holmes, from the Queensland Environmental Services and Regulation's incident control response unit, said there was a misplaced trust in "PFOS-free" foams.

"That's true while it's still in the drum but once it's used you have the potential to generate (PFOS)," he told an inquiry into Fiskville centre on Monday.

"The problem has not gone away when we stopped using PFOS foams."

He said the chemical chains in PFOS still exist in new foams, and they could join together once other parts of the chains degrade when the foams are used.

Mr Holmes said there was still so much not known about the impact of firefighting foams on people and the environment.

"We should not using (PFOS), we should not be releasing it because the effects are well known but it's only one of hundreds," he said.

The hearing continues on Monday.