Monday's release of the report, written by research professor William Mitchell and research fellow Beth Cook and commissioned by the firefighters' union, comes days before the Auditor-General releases a report expected to show high rates of unplanned leave by professional firefighters.

It is understood the state government believes the university's report is an attempt by the union to pre-empt the Auditor-General's findings.

The university report warns that ''given the psychological impact of firefighting - higher prevalence of PTSD [post-traumatic stress disorder], depression, anxiety and alcohol or drug use - there is a probability that firefighters may be more likely to commit suicide''.

Firefighters union secretary Peter Marshall said the report - including figures from one study showing 68 per cent of firefighters recorded moderate symptoms of PTSD - revealed firefighters were sitting on a ''ticking psychological time bomb''.

He said existing support programs, which include a peer-to-peer service, were inadequate and budget cuts to the metropolitan and country fires services had exacerbated the problem. ''The government is drawing on the physical and mental reserves of firefighters like never before but not giving them the support.''

But a spokesman for Deputy Premier and Emergency Services Minister Peter Ryan said ''this year's fire services budget was the second-biggest on record, surpassed only by last year's budget'', which paid for many of the bushfire royal commission recommendations.

The spokesman said the government would wait to read the union-commissioned study before it responded.

The Metropolitan Fire Brigade's chief officer, Shane Wright, stressed that existing support programs were comprehensive and effective.

Mr Wright also said that, compared with other emergency services, firefighters had smaller incidences of stress-related WorkCover leave.

Metropolitan firefighters interviewed for the report singled out stress factors including ''the introduction [in 2000] of Emergency Medical Response [in which firefighters are first respondents to medical emergencies] and the ageing of the workforce in the MFB'', while professional CFA firefighters ''singled out the deterioration in the numbers and reliability of volunteers as the single most notable change for the organisation''. Asked to rank their most stressful incidents, metropolitan firefighters listed fire fatalities and dealing with seriously injured children or the sudden death of an infant.

The report states: ''Participants were concerned that the intensity and level of exposure increased over time and left all firefighters vulnerable to PTSD as their career progressed, and even after retirement, when they lost the support of co-workers. Some participants expressed a belief that many firefighters suffered from undiagnosed PTSD or depression.''

The focus groups also reported perceived insufficient support from management to deal with stress.

However, the study also noted firefighters were often reluctant to seek help, sometimes preferring to self-medicate with alcohol, and that the existing data around stress levels was incomplete.

A 30-year firefighting veteran, Danny Ward, told Fairfax Media that while he and his colleagues were well trained to deal with fires, they are not sufficiently supported to deal with the mental impact of attending car accidents, cot deaths, heart attacks and drug overdoses.

''You don't tell the kids and wives about the day that you've had. You just go upstairs and lie in bed,'' Mr Ward said. ''The PTSD problem is just waiting to explode.''

For help or information call Suicide Helpline Victoria on 1300 651 251 or Lifeline on 131 114, or visit beyondblue.org.au.