VICTORIANS who install bunkers as a last resort during catastrophic bushfires face an extra fear - unwanted guests.

Managing director of Wildfire Safety Bunkers Anthony Tratt said most of his clients were aware of what he called "scrambling", where strangers may invade private refuges when a major bushfire threatens.

"People don't want to advertise the fact they have got a bunker - they just tell their immediate neighbours," Anthony said.

His Somerville-based company has built bunkers in bush areas in East Gippsland, the Yarra Valley and Dandenong Ranges as well as in flat grassland areas, including the Mallee.

One such buyer, Drew Gordon, lives with his family on a sloping one-hectare block in a forested area along the Yarra River valley.

"Our immediate neighbours are aware of it, but they are looking at getting one themselves," Drew said.

The Gordons decided to install the bunker because they live in a bushy area, with difficult access, and care for an elderly relative and some beloved dogs.

"The night it (the bunker) went in, and they (the installers) drove away, it felt like a huge weight lifted off our shoulders," Drew said.

Another buyer, Bevan Gobbett, survived the Black Saturday firestorm at Clonbinane with his family by taking refuge in a buried shipping container with basic fire protection.

Bevan has now rebuilt and lives with his wife, Jodie, and daughter, Lauren, on the 2ha property where they were forced to shelter on February 7, 2009.

Bevan's advice to people planning to build their own refuge was "don't do it".

"People will end up killing themselves if they think they can survive another Black Saturday," he said.

Bevan said that when the blaze hit more quickly than expected, the buried container became "a refuge of last resort".

Coroner's Court officials and other investigators told him his family "should all be dead" because of the inadequate fireproofing of the container.

"My wife had to hold the door shut because the fire had sucked it open," Bevan said.

"She got burnt on the face from doing that.

"We had to put respirators on - as the bushfire went across the container, it all got filled with smoke."

Bevan said people started calling the container a fire bunker when they heard of their escape, but it was only ever meant to be a storage area.

The Victorian Government's Building Regulations Advisory Committee introduced statutory rules on November 11, 2009, that govern the construction of private bushfire shelters.

A Victorian Building Commission spokesman said BRAC had begun to issue certificates of accreditation to approved bushfire bunker manufacturers, with Anthony Tratt's Wildfire Safety Bunkers among the first to qualify.

A VBC spokeswoman said an owner-built bushfire shelter worth less than $12,000 could still be built and then certified if the correct steps were taken.

Any owner-built bushfire shelter costing more than $12,000 must have a certificate of consent from the Builders Practitioners Board and a building permit before work starts.