The leaking of the report will throw the spotlight back on Premier Daniel Andrews' handling of the CFA crisis, and his close relationship with the powerful United Firefighters Union.

The report is based on confidential survey responses from 550 CFA professional staff, some of whom expressed fear to researchers that their identities would become known by bullies in the organisation if they spoke honestly.

Some women who had been sexually harassed or assaulted had been driven to illness, or even the brink of suicide.

The alarming findings of the leaked Interim Report on Gender Diversity and Inclusion show that half of both male and female respondents reported being bullied, and one-third had been harassed, including sexual harassment.

The report takes particular aim at the firefighters' union, which it says perpetuates a culture of "no transparency or accountability", and an industrial agreement that "counters any attempt to address even the most serious forms of reported conduct".

The revelations come as a small group of former senior Metropolitan Fire Brigade firefighters have formally complained to the MFB that it failed to protect them from entrenched union bullying, with one having been sent a bullet in the mail.

The Andrews government claims it is committed to dealing with reports of bullying and harassment in the CFA and MFB, and has initiated an inquiry by Victoria's human rights commission. But the commission's inquiry has been blocked in the Supreme Court by the union, which argues its methodology is flawed and its inquiry biased.

The report, written by two CFA staff members, Professor Caroline Taylor and Angela Seach, relies on detailed responses to a survey commissioned by former organisation chief executive Lucinda Nolan.

Ms Nolan quit the organisation a month after the report began taking responses, after the Labor government caved in to union demandsand increased its control over CFA operations. That deal also prompted the resignation of emergency services minister Jane Garrettand the sacking of the CFA board.

Now, the leaked internal CFA report, which in part fed into the human rights commission's report, has exposed the CFA's hidden problems, suggesting it is an unsafe workplace.

"Of considerable concern is the reporting of sexual assault and sexual harassment by several female staff, with one respondent citing they have contemplated suicide as a consequence of the responses they have received from CFA management to their complaint," the leaked report says.

Another respondent stated that their report of sexual assault in the workplace was "aggressively rejected by their manager, leading to them feeling unable to report the matter further.

"These behaviours are serious breaches of conduct and likely to have involved criminal behaviour and it is deeply concerning that staff have reported not only the assaults but the appalling and harmful responses when seeking to report them through their supervisor/manager," the report says.

"Literally hundreds and hundreds of respondents gave detail of behaviours that included criminal sexual assault; sexual harassment; physical altercations; bullying; intimidation; harassment; threats of violence and other forms of inappropriate behaviour causing various degrees of distress."

"The sheer volume and content of qualitative data addressing bullying, harassment and other inappropriate conduct speaks to the seriousness of the issue."

The interim report on the professional, technical and administrative staff survey also warns that "several respondents identified that they had contemplated suicide".

"Others… had to seek psychiatric and medical intervention to support levels of stress, depression, anxiety and suicidal ideation as a result of serious workplace conduct directed towards them.

"Many other respondents wrote of needing to take medical leave as a direct consequence of bullying and harassment as well as requesting to be moved away from the department, locale or even district where they were working as a means of avoiding ongoing bullying and harassment.

"Even more concerning are comments from staff in the survey expressing levels of genuine fear, apprehension and mistrust that completing the survey may lead to them being 'identified' or that information may be used to reveal their identity, leading to a punitive repercussions.

"Several respondents went as far as making pleading comments in the survey that their comments would not quoted in full for fear that even the wording they chose to articulate their experiences of bullying, assault and harassment may mean that they are identified by the offender or other staff within CFA."

The report says some staff believe the union, which maintains a relatively small but powerful presence in the CFA, contributes to a culture in which "management and in particular operational staff bully and harass with impunity as a consequence … of an organisational culture that has no transparency or accountability."

One example describes a female staff member being told by a manager that, as "the person doing the bullying was a UFU member and as I was on a contract, this person could do serious harm to my ability to continue in my role because they would 'target' me further and inform other 'management' and ensure I was not offered further work.

"My then manager asked me to 'be the bigger person' in this and just ignore it for my own wellbeing."

In a statement, the union's lawyers said on Monday that the UFU denied it had contributed to poor workplace practices and that claims it supported bullying or harassment were baseless and part of a concerted media campaign.

The report describes as significant the fact that more than half the CFA's professional, technical and administration staff responded to the survey and of those, 97 per cent provided "detailed comments of experiences affecting them or others they had witnessed occurring to other staff".

CFA staff "frequently" identified a "boys club" culture that protects people behaving badly. 

"Protection from accountability for poor performance and poor behaviour is entrenched within CFA," the report states.

It provides comments given by one male CFA staff member, who describes the existence of a "brotherhood", and wrote that "the boys club culture is still very strong, with the expectation that you will not rat out anyone unless the behaviour is really outrageous."

Another male described "a manager brag to me that when he was running a project in HQ he made sure that his female team was 'worth looking at all day'. "I'm approaching 30 years in the public sector and have been witness to all manner of behaviours, but I've never seen the like of CFA before."

In response to questions from Fairfax Media about the report, a CFA spokesperson said the agency had appointed a dedicated assistant chief officer for inclusion and fairness and "significantly improved our complaints procedures, adding more staff and making it easier to raise issues in a confidential and safe environment". The spokesperson said the CFA had zero tolerance for any inappropriate behaviour and was introducing a fairness and inclusion education program.

Emergency Services Minister James Merlino said multiple reports had pointed to problems within the fire services "including a poor relationship between management and the workforce and a lack of diversity within its ranks".

"Creating real cultural change isn't easy but we want our fire services to reflect our diverse modern state and that's why we have set ambitious targets to increase diversity and are backing this up with the investment needed," he said.

Nepotism is also described in the leaked report as contributing to problems inside the agency.

"Another major issue that I believe contributes to this culture is the favouritism shown to friends and family. There seems to be a glut of these people who have been hired based on their community ties not on their suitability or qualifications for the job …

"These people often get unadvertised jobs through word of mouth and once they are in they contribute to the bullying culture as they are free and protected to do what they want."

Male and female CFA staff identified bullying and harassment as a major issue. Women who went on maternity leave were treated as if they had a "lobotomy"; one staff member commented that "it seems to take until a staff member/s get to the point of breakdown before any action is taken"; another staff member was "chested" by her manager and instructed to put in writing why she wanted to work for him; a male CFA staff member likened the CFA culture to " the Mafia … if you try and stand up against it you are dead".

The report concludes that: "the sheer volume of qualitative data ... indicate serious behaviours reported across the organisation and an organisation seemingly unable or unwilling to deal with poor behaviour".

This led staff to the view that, "the organisation both tolerates such behaviour and punishes victims or others who seek redress".

"Many respondents expressed a view that bullying and harassment are rife, everyday conduct within the organisation and practised at every level of staff and management."

"There was a powerful consensus that CFA cultivated and maintained an unhealthy culture where bullying, harassment and other inappropriate, and indeed criminal conduct, was deeply embedded."

With Benjamin Preiss, Gina Cerasiotis