(NECN: Nicole Jacobs, Boston) - The scene was massive - the blaze destructive - as 31 Massachusetts Avenue in the Back Bay section of Boston fell victim to fire.
Ladder trucks and firefighters battled the blaze in the six-floor building.
According to the Boston Fire Department, fire investigators say the fire was caused by the careless disposal of smoking material on the fifth floor.
"At one point, we about had the most volume of fire you can have coming out of the apartment's two windows," said Boston Fire Deputy Chief Joseph Fleming.
It escalated to seven alarms, blocking off countless roads, just to make way for firefighters to do their job.
"We do a primary search on the fire floors, so we checked every apartment, and we also do a secondary search afterwards, just to make sure, so we didn't find anybody," said Fleming.
Adding to the fast-moving flames, the building is one of 50 in the city of Boston that doesn't have updated sprinkler systems, simply because of the language of the law.
"We're going to look at this now, and talk to the legislature and see if we have to file something to catch these other buildings," said Mayor Marty Walsh.
Upwards of 40 people were displaced.
David Schwartz lives on the sixth floor, where the fire spread.
"They told us there's water damage, there's smoke damage, there's heat damage," he said.
And the damage is extensive - an estimated $2.5 million so far. But even with that, there is the calm of knowing no one was hurt.
"They told us everybody had been accounted for, so there's a big relief there," said Schwartz.
But as residents are escorted inside to gather whatever belonging they can, it's unclear when they'll be allowed back and just how much they're able to salvage.