ORONO – Fire inspectors have determined that a midafternoon fire that destroyed the second-floor apartment of a Main Street building Thursday and displaced nine University of Maine students was accidental in nature.

A candle located in the upstairs bedroom where the fire started could not be ruled out as the cause, according to fire investigator Ed Archer of the state Fire Marshal’s Office.

More than 30 firefighters from six fire departments spent two hours fighting the blaze at 88 Main St. The nine tenants and a cat were uninjured in the fire, although three firefighters were treated for minor injuries at the scene.

Archer said that an inspection unit is looking into the building itself and investigating issues of code, life safety, electrical system, smoke detectors and occupancy. The apartment had a working smoke detector, Archer said.

A smoke detector in each bedroom could have provided an earlier warning, according to Chief Lorin LeCleire of the Orono Fire Department, which also was looking into the cause of the fire.

The bedroom door was closed when the fire started, giving it time to develop, LeCleire said Saturday. Originally reported as a mattress fire, the flames moved up and into the room’s wooden wall and into the attic, he said. He estimated that the fire was burning in the attic for 45 minutes to an hour before a tenant heard a popping sound just before the power went out.

That popping sound was the fire burning in the walls, LeCleire said.

LeCleire said he guessed the house would not be rebuilt and the building would have to come down.

Few things on the second floor were recoverable from the fire, LeCleire said. Almost everything, except for a few articles of clothing and some personal effects, was severely burned or water-damaged, he said. First-floor occupants were given a chance to recover what they could, some of which was wet, not burned, he said.

One second-floor tenant received an unexpected surprise Friday when some jewelry she recently received was recovered unharmed. Before a search of the apartment, Sarah Lowery’s fiance, Doug Foster, had mentioned to firefighters the approximate location of the jewelry, LeCleire said.

While sifting through the rubble around 10 a.m. Friday, Lt. Bryan Hardison found a gold necklace and pendant under a piece of fallen furniture, LeCleire said. In the bathroom, firefighters recovered an engagement ring. The jewelry was worth roughly $4,500, LeCleire said.

Lowery arrived back at the scene around noon and Foster already had taken the jewelry to G.M. Pollack in Bangor, where the jewelry was purchased. Employees of the store cleaned the ring and the pendant and setting and replaced the necklace, which had been burned into a section of carpet, Lowery said Monday.

“It was amazing,” Lowery said. “The necklace I could have let go, but the ring was one of the few things I wanted back, and it was the only thing weighing heavily on my mind.”