But Emergency Services Agency commissioner Dominic Lane stressed that ACT Fire and Rescue was only a small part of fire authorities' overall response to bushfires, with the Rural Fire Service taking primary responsibility. He also said the planned changes would have no impact on public safety.

A draft copy of ACT Fire and Rescue's new bushfire and storm enhanced crewing policy, obtained by the Sunday Canberra Times, shows that on days when the fire danger rating reaches level three – very high – the service would be required to stand up four tanker crews or four compressed air foam system crews.

The extra vehicles would be crewed by dedicated staff from 12pm until 6pm.

While the draft of the new policy would require either an additional four tanker crews or four compressed air foam system crews, the current policy states that four of each are needed on days of very high fire danger.

In a scathing email to ACT Fire and Rescue chief officer Mark Brown on Thursday afternoon, United Firefighters Union ACT branch secretary Greg McConville blasted the proposed changes.

"Let's call this what it is: a reduction in the level of fire protection driven by the failure of ACT Fire and Rescue to recruit sufficient staff," Mr McConville wrote in the email, which he forwarded to the Sunday Canberra Times.

Mr McConville last year said ACT Fire and Rescue was about 40 firefighters short of its funded establishment, but Emergency Services Agency commissioner Dominic Lane called that claim a falsification.

In his email to Mr Brown, Mr McConville said the deployment of the compressed air foam system appliances arose from the inquiry into the devastating 2003 Canberra bushfires, headed by former Commonwealth ombudsman Ron McLeod.

"The Canberra community would rightly be aghast that the [Emergency Services Agency] continues to wind back the gains in fire protection made after the review into the fires that caused the deaths of 4 people, injured 490 people, and destroyed 470 homes," Mr McConville wrote.

Mr McConville also savaged the Emergency Services Agency's approach to consultation with the union, calling it "hollow, cynical and tokenistic".

Mr Brown was not available for interview on Friday, but his boss, Mr Lane, told the Sunday Canberra Times he fully supported the proposed changes.

Mr Lane said ACT Fire and Rescue was primarily an urban fire service and the ACT Rural Fire Service held the main responsibility for fighting bushfires in the territory.

He pointed out that on the fire danger rating scale, which has six levels, "very high" was in the bottom half of risk at level three. No changes to crewing levels were proposed at the more elevated levels of risk.

"It’s very much about, well, what’s the risk, and do we need all those [firefighters] stood up?" Mr Lane said of the proposed changes.

"I have a personal view that we should make sure that the taxpayer gets best value for money, but also that our own people don’t find themselves fatigued because they’re stood up more than they need to be, so it’s about getting that right balance.

"We think we can very confidently make a change to ACT Fire and Rescue’s stand-up arrangements without compromising public safety, but that's part of ongoing correspondence between the firefighters' union and the chief officer."

Mr Lane said decisions about crewing were not only dictated by the minimum requirements at each fire danger rating level.

He said decisions were informed by the agency's dynamic coverage tool, which took into account the active resources available, the fire danger rating and known data about the history of fires in the ACT.

"Rest assured, we’re not going to have an issue in terms of not having enough resources," Mr Lane said.

"The ACT remains the best-resourced jurisdiction in the nation in relation to bushfire risks."