Despite a directive by United Firefighters Union boss Peter Marshall not to take part in the investigation, a growing number of career and volunteer firefighters have participated, setting the scene for a dramatic shake-up of the male-dominated profession.

The inquiry was commissioned by the state government after the Fire Services Review found a culture of bullying in the Metropolitan Fire Brigade and the Country Fire Authority as well as a lack of gender diversity, with figures suggesting only 3 per cent of the workforce are women.

However, the union hit out immediately, accusing the Victorian Equal Opportunity and Human Rights Commission of lacking independence and declaring it was "not in members' interest" to participate.

"We are also greatly concerned that there does not appear to be any controls or protections in place to ensure full and frank reporting and validation of the outcomes," Mr Marshall wrote in a memo to members after the inquiry was launched in July.

With investigations ongoing, Commissioner Kristen Hilton declined to comment on what had been uncovered so far, but confirmed the themes were similar to an earlier review her organisation conducted into Victoria Police.

That review, released last year, painted a troubling picture of a workforce plagued by sexual harassment, predatory behaviour, and a culture of discrimination – all of which Police Chief Commissioner Graham Ashton has vowed to address.

Ms Hilton said she was surprised the UFU had actively discouraged its members not to participate in the review, contrasting its resistance with the Police Association which had been "completely on board" with the objectives of the commission's inquiry into Victoria Police: to provide a safe, inclusive and respectful workplace for its members.

Asked about the response so far, Ms Hilton told Fairfax Media: "We're certainly hearing stories that pick up on the particular terms of this review, which includes bullying, equity and diversity.

"In the first 48 hours we had over 800 responses to the survey, and the number of people that have called us and asked to speak with us directly has exceeded our expectations in terms of how many people we would get. The representation we're getting is also mixed, so we're getting people from the CFA, the MFB, and we're getting both paid and volunteer firefighters."

The commission will continue to gather evidence, visit stations and talk to firefighters until mid-November before producing a series of recommendations that could shake up the profession.

But unlike the police review this inquiry is taking place within a dicey political climate, with Daniel Andrews under sustained fire over his handling of the CFA dispute, which has led to multiple casualties, including that of former minister Jane Garrett who quit cabinet in June after refusing to adhere the union's demands.

Gender diversity is also a sensitive topic in emergency services, with the Commission's review expected to throw the spotlight on a series of systemic problems that are holding women back or discouraging them from becoming firefighters. Emergency Services Minister James Merlino​ has made it clear that he wants the issue addressed.

"Our communities are diverse so it goes without saying that our emergency services should reflect this," he told Fairfax Media earlier this year.