The University Laboratory School's old Elementary Building, which burned to the ground on Tuesday, was built in accordance with the Uniform Building Code of 1929.

In the 77 years since, the code has been updated 15 times. But the school — like all buildings and houses on O'ahu — was not required to be upgraded to meet current code standards.

It "was always a target hazard because it was all wood," said retired firefighter Richard Soo, who is now a fire safety inspector for the state Department of Education.

"We would pre-plan the possibility of a fire at that location as opposed to other locations in the Manoa area," said Soo, who worked at the Manoa Fire Station.

He insisted that doesn't mean the building was unsafe. It had a safety plan and always passed its annual fire inspections, just as it did when it was inspected last on Nov. 21.

But unlike most public schools on O'ahu, which are generally built with hollow tile construction, according to Soo, the Lab School's wooden construction and high ceilings posed potential hazards.

"When you looked at that building, it had a huge high roof," he said. "And once the fire penetrated through that ceiling, it just got complete access to the void space in the attic."

Soo said firefighters realized years ago that should a fire ever reach the attic, it would rapidly engulf the building.

Which is why firefighters were removed from Tuesday's inferno about 20 minutes after they arrived, said fire spokesman Capt. Kenison Tejada.

Firefighters had first gone inside the structure, the most effective location from which to extinguish a fire, Tejada said.

He said the fire appears to have started on the 'ewa end of the structure, near the restrooms and drama room. That section was in flames when firefighters went inside.

Once the fire reached the attic, the large overhead space rapidly created convection currents that sent the fire raging through the building at least 50 feet ahead of where it was burning down below, Tejada said.

When it became apparent that the fire had moved up and over firefighters inside the building, they were told to get out.

"As were were pulling them out ... we could see small pockets of fire burning through the ceiling," Tejada said. "And right after we got them out, the ceiling started to collapse."

Reach Will Hoover at whoover@honoluluadvertiser.com.