New London — An investigation found that a house fire  that displaced 15 people Sunday afternoon was an accident caused by "smoking materials," according to fire officials.

The fire, which broke out at 1 Farnsworth St. about 4 p.m. Sunday was caused by "smoking materials being improperly disposed of on a window sill," according to a statement released by city Fire Inspector David Heiney on Monday.

No one was injured in the fire, but 15 people — nine adults and six children — were displaced from their homes, which Heiney said sustained moderate damage.

The fire started near the window sill and traveled into the three-story family home, the investigation found.

Fire Chief Thomas Curcio said the fire caused damage on all three floors. He said it looked as if the fire went up between the walls all the way into the attic area.

"We had to open up the roof and open up all the walls," Curcio said.

In his statement, Heiney issued safety tips to avoid fires caused by smoking materials, including properly disposing cigarettes into an approved metal container, smoking outside, using a proper ash tray and never smoking in bed. The inspector did not specify what type of smoking materials sparked the blaze.