The Victorian Ambulance Union wants metropolitan-style digital radio rolled out across regional Victoria after an outage knocked out VHF communications across Ballarat and beyond.
Between 12.30pm and 2.30pm Monday, paramedics in the Grampians region were without two-way radios and were left with only their mobile phones for communication.
It also affected the Barwon-South West and Gippsland regions and comes two weeks after a similar outage across the state's northern half, including Bendigo.
"All five of Ambulance Victoria's country regions have been affected now - and yesterday's outage was over a much bigger area than the first," Secretary Danny Hill said.
"The metro area switched to digital radio communications in the early 2000s - so doing this in regional areas is now well overdue."
Monday's outage took place during two significant incidents in the Ballarat region: a large hazardous materials spill that blocked the Western Freeway at Wendouree from 1.30pm, as well as a series of spot fires that closed the Sunraysia Highway between Waubra and Lexton from 12.30pm.
"The state government said no one was seriously hurt during the blackout, but I don't buy that," Mr Hill said.
"It's like throwing a big rock into a crowd and then working out that no one got hurt.
"It's still incredibly dangerous."
He said the analog radio communications system had worked well in regional Victoria for decades - and while the source of Monday's blackout was unknown - he believed the aging equipment was breaking down.
"These older systems are prone to failure," Mr Hill said.
"It's alarming that we've had widespread communication crashes affecting dozens of our area's ambulance stations.
'There have been several tragedies on rural roads over the last few weeks - including what happened at Daylesford."
On Monday, paramedics relied on mobile phones to communicate, and Mr Hill said when the mobile signal was unavailable, paramedics, in general, had to rely on someone to drive to the nearest mountain. At the same time, crews got to work as best they could.
"Communications are critical - the first thing you do when you get to the scene is triage.
"You would normally radio back and ask for extra resources, air ambulances, get people to notify hospitals if there are a lot of casualties, and talk about hazards at the scene.
"The other part of it is around occupational violence. If there's a risk, paramedics must ask for police before entering the scene.
"All that is done with the radio."
Mr Hill said the metropolitan digital system was reliable - but the main factor preventing its statewide rollout was a network of costly repeater towers.
"You could put these digital radios in ambulances tomorrow - but they need the repeater towers," he said.
"They've had 15 to 20 years to do all of this."
The metropolitan digital radio system was set up before Rural Ambulance Victoria and the Metropolitan Ambulance Service merged in 2008.