Back-burning failed to quell the Christmas Day bushfire on Victoria's surf coast, but the blaze may have been far worse without it, Emergency Management Commissioner Craig Lapsley says.
The fire, which destroyed 116 homes, was sparked by a lightning strike on December 19.
Three days later, a back-burning operation was ordered to reduce dry fuel in inaccessible bush around the fire, then covering less than one hectare.
The government says the state's emergency management inspector-general will investigate.
Mr Lapsley says the decision to burn was risky but was taken to reduce the fire's intensity.
He said back-burning was the best of a bad lot of options.
"We reduced the fuel (with back-burning) so it wouldn't come out as a raging bull," he told 3AW on Thursday.
"Nothing else was working. We knew if we didn't do something, the intensity of the fire would mean we probably would have seen a fire triple the size, or more."
He will meet affected residents to explain the decision.
United Firefighters Union secretary Peter Marshall is demanding a coronial inquiry into whether the burn and the bushfire are connected.
He said the investigation is beyond the inspector-general's powers and resources, and the coroner can probe non-fatal major incidents.
Wye River resident Sherryl Smith lost everything in the blaze.
She backs an independent inquiry, and says crews should not have fought the fire with water.
"If they used a quarter of those resources they have used since then, we wouldn't have had a problem," Ms Smith told AAP on Thursday.
"What happened here is that a back-burn happened that shouldn't have happened ... with disastrous consequences."
Environment Minister Lisa Neville praised firefighters' efforts to limit the bushfire to 2500 hectares, saying they are "extremely distressed" at questions about their tactics and commitment to community protection.
She said all chief fire officers, including Mr Lapsley, have the government's full support.
The Department of Environment, Land, Water and Planning was savaged by a report into a controlled burn it set near Lancefield that destroyed four homes and 3000 hectares in early October.
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