City investigators have determined the cause of a fire that destroyed a nearly century-old apartment building in Squirrel Hill last week and left the people living there without a place to go.

The fire started in a basement utility room and was electrical in nature, Pittsburgh Public Safety officials said. They added that it was accidental.

About 30 people were forced to evacuate from the burning Jefferson Apartment building as the fire quickly spread and heavy smoke billowed high above the neighborhood.

The building is now in the process of being torn down. 

The large, four-alarm fire in the building on Forward Avenue took four and a half hours to get under control. There were 44 units in the building and about 30 of them were occupied.

What looked like one small fire on the end of the building soon had the entire building burning due to its 1920s architecture of brick and full wood framing. 

"It's kind of surreal, honestly. I wasn't on the third floor, like I said, so I wasn't in immediate danger but seeing them work on it, and then seeing it look like it calmed down for a bit and then flare up, then suddenly the roof collapsed. It's a lot to take in all at once," one resident said.

Everything inside was lost, but everyone inside was saved. All the residents got out, and no one was killed or injured. Public Safety said two cats were rescued, but a third was found dead. 

Demolition process now underway

Demolition of the apartment complex began Sunday night. However, some residents were caught off guard by the unorthodox demolition schedule and several inconveniences that may come with the demolition process.

Mark Goldberg, who owns an apartment building next door to the destroyed structure, says his tenants are upset.

"First of all, they had to evacuate on Tuesday and Wednesday.  Some of them came back on Thursday, and the rest of them came back on Friday. So, I'm concerned about their safety, their welfare. They're good tenants," Goldberg said.

 One resident said, however, that they still lack utilities such as hot water and gas.

"We have no hot water, and we have no gas. We were just allowed back in the building two days ago, but we're told to stay on notice for further changes," resident Jeff Moye said.

Residents also said they have been given no indication about how long the entire process could take.

Crews responsible for the demolition said it will take place at "off-peak hours" to ensure maximum safety for residents, workers, and passing vehicles.

Tim Schaff, owner of Schaaf Excavating Contractors, Inc., was hired by the building's owner to assist with demolition. 

Schaff has also worked with the city of Pittsburgh for 30 years. He said safety is the No. 1 priority during a project like this.

As for how long the demolition will take from start to finish, residents should expect about one week of demolition during off-peak hours and 10 days of debris removal. Removal can happen during daylight hours. 

Utilities may also be periodically shut off to ensure safety.