Story updated: 2:28 p.m. Friday.

Improperly disposed of smoking materials on the back deck caused a duplex fire earlier this week in Lawrence, fire officials said.

The fire, ruled accidental, broke out shortly after 5:30 p.m. Monday at a two-story duplex at 3407 Harvard Road, Lawrence-Douglas County Fire Medical Division Chief Tom Fagan said in an email.

Firefighters, who arrived to find flames coming from the deck, had the fire under control in about 30 minutes, Fagan said.

All human tenants got out of the building on their own, uninjured, Fagan said. He said firefighters rescued three cats and three dogs, none of which were injured.

Damage to the home was estimated at $20,000, he said.