Investigators say a fire that ravaged a building at 458 Central Ave. in Hamilton Thursday night, displacing 20 people, is believed to have been accidental.

“We don’t know what the exact cause of the fire was, but we think it was accidental,” said Fire Marshal Tom Angst.

One person who was not accounted for was apparently not caught in the blaze, as Hamilton firefighters spent Friday morning searching through the debris, Deputy Chief Jeff Shaw said.

Angst said the man was later found to have been in Middletown at the time of the fire. He said the structure was not a total loss as damages are estimated at $90,000.

Firefighters were dispatched about 8:19 p.m. to the structure where they found heavy fire throughout the third floor of the building, said Deputy Chief Lawrence Gassert. The third floor was originally a common attic area that had been converted into an apartment.

Gassert said the initial fire crews began assisting in the evacuation of the residents from the first and second floors while other crews began fighting the fire on the third floor. Fire crews encountered multiple stairways with some leading into dead ends, forcing the crews to retrace their steps, Gassert said.

The fire, which was already engulfing the structure, continued to burn roof supports, forcing the fire crews to be evacuated. At that point, the roof collapsed with firefighters taking a defensive position to keep the fire from spreading elsewhere. Gassert said the fire was finally extinguished using an elevated stream of water from a ladder tower truck. Firefighters spent three hours fighting the blaze.

After the fire was knocked down, the structure was evaluated for soundness and crews returned to the site to extinguish the remaining hot spots and to overhaul the fire, Gassert said.

There were no injuries to the residents or firefighters fighting the blaze. The Red Cross was contacted and was assisting residents who were displaced by the fire.