Firefighters are demanding the Hazelwood mine inquiry examine power company SP AusNet over fears ash falling on its power lines may have triggered a massive electrical explosion.
More than 80,000 people lost power when live power lines came crashing down near the town of Morwell in Victoria's east.
Morwell explosions cause Gippsland power outages
RAW VISION: Morwell resident Jaye Atlee posted the video to YouTube, saying: "Caught this video of the explosion in Morwell just as the power went out."
Huge explosions from the town's major substation could be heard several kilometres away on Friday morning as snapped power lines scattered raw electricity into fences, sparking several grass fires.
United Firefighters Union secretary Peter Marshall said the incident could have ballooned into a catastrophic event if it had been a hot summer day.
"It could have been a lot worse. We need to know what happened," he said.
He said the incident now needed to be probed by the independent inquiry set up after the nearby mine fire blanketed everything in a thick layer of soot.
Firefighters reported seeing ash building up on power lines from that blaze for weeks before Friday's explosion.
SP AusNet has so far not ruled out a build-up of ash as a contributing factor to the major power outage.
"There are no conclusions at this stage," a company spokeswoman said.
"All lines and assets are inspected and maintained to meet with regulatory obligations."
LaTrobe City Councillor Graeme Middlemiss said the risk of dirt and moisture triggering major faults on power lines had been known for decades.
"We had ash raining down in that area continually for about seven weeks, so I think it would be very appropriate for this to become part of the broader Hazelwood inquiry," he said.
The power outage has so far been traced back to a 66,000-volt line near the Morwell Terminal Station, according to a source familiar with the investigation.
The line fell on to other power lines, causing a rapid power surge that cascaded through the system.
The Hazelwood mine inquiry will begin on Thursday and is being led by former Supreme Court Justice Bernard Teague, who also led the state's bushfires royal commission.
State opposition energy spokeswoman Lily D'Ambrosio said the government first needed to ensure the electrical regulator probed the explosion to confirm a link existed with the ash before the inquiry could examine it.
"The people of Morwell deserve to know whether there is any possible relationship with the build-up of ash and the explosion that followed," she said.