Water at the Country Fire Authority's (CFA) Fiskville training base in western Victoria was allegedly deliberately contaminated as part of a biological experiment, a Victorian parliamentary inquiry has heard.

The inquiry is examining claims dozens of firefighters who worked or trained at Fiskville suffered cancers linked to dangerous firefighting chemicals over several decades.

Metropolitan Fire Brigade firefighter Mick Tisbury told the inquiry a scientist told him the potentially dangerous bacteria and fire retarding organism, pseudomonas aeruginosa, was added to water at the base as a cheap way to treat hydrocarbons.

"He told me that he was part of an experiment with the CFA where they deliberately introduced pseudomonas aeruginosa into the water supply as a biological way of cleaning up the hydrocarbons in the water," he said.

Mr Tisbury, who was an instructor at Fiskville, said the CFA was aware of contamination at Fiskville as early as 1988, as a result of a series of independent reports, some of which were commissioned by the CFA.

He uncovered a February 2007 Ecowise report showing disturbing levels of pseudomonas aeruginosa, which can cause infections, in one of Fiskville's dams.

The bacteria is safe at a level of fewer than 10 organisms per 100 millilitres, but test results showed the dam had 33,000 organisms per 100 millilitres of water.

"The presence of pseudomonas aeruginosa at these levels indicates the water is unsuitable for primary contact," the report said.

CFA 'knowingly' put recruits at risk

The inquiry heard CFA chief executive Mick Bourke received another report concluding firefighters were at risk at Fiskville after the discovery of a cancer cluster in late 2011, yet he publicly declared the base was safe and let training continue.

Mr Tisbury said the CFA knowingly put the health of recruits at risk.

"If you do bugger up and do expose your people to it, tell your people what you've done. Don't cover this up," he said.

"As an instructor I am very concerned that I have unknowingly subjected recruits to train in, and with, contaminated water."

Mr Tisbury said he had received death threats and been spat on in front of his children since he spoke out about contamination at Fiskville.

"When I was spat on, the comment was 'that's for Fiskville'," he said.

Calls for prosecution over alleged workplace safety breaches

Former Fiskville instructor Tony Martin told the inquiry the former head of the training college, Justin Justin, was promoted after ignoring information about toxic chemicals in the water used for training exercises.

"He didn't take care of his people," Mr Martin said.

"He told me a lot of untruths. He put us all at risk."

Mr Justin resigned from the CFA last December.

Mr Martin has been treated for prostate cancer, a benign tumour in his pancreas, two cerebral aneurysms, headaches, skin rashes and back pain.

"Enough is enough," he said.

United Firefighters Union state secretary Peter Marshall said people should be prosecuted for breaches of workplace health and safety legislation.

"Those people who did not convey that information to the firefighters, who put the firefighters at risk, we want them made accountable and we want them prosecuted," he said.

"I'm in no doubt that they knew and didn't tell."

Former CFA employee Michael Whelan told the inquiry the CFA was "arse-covering".

"My scorn today is reserved for the CFA board," he said.

"I consider their denials over two decades, denials of justice for people, to have been quite disgraceful.

"They've done nothing. They've been in damage control mode. They've failed miserably and they should suffer the consequences."

Mr Whelan said the absence of a public apology must be hurtful to the families who had lost people to cancer and other health problems.

The CFA shut Fiskville in March.

An interim report is expected to be tabled in Parliament later this month.

Organisations including the CFA and Environment Protection Authority will give evidence during the second stage of the inquiry.