ORRINGTON, Maine — Empty cardboard boxes stored too close to a wood stove started the deadly fire in Orrington on Saturday that killed a father and his three young children, the state fire marshal’s office said Monday. It was the deadliest fire in Maine in 20 years.

The state medical examiner’s office said the four died from smoke inhalation. The bodies of the three children were found on the floor of a second story bedroom and the father’s body was found at the head of the stairs, also on the second floor.

Investigators met with the only survivor, Christine Johnson, 31, in her Bangor hospital room Monday morning and informed her of their findings, said Stephen McCausland, spokesman for the Maine Department of Public Safety.

Christine Johnson’s husband, 30-year-old Ben Johnson III, their sons Ben, 9, and Ryan, 4, and 8-year-old daughter, Leslie, died in the fire at 580 Dow Road early Saturday morning.

Christine Johnson was being treated for smoke inhalation at Eastern Maine Medical Center.

Fire investigators said the home was heated with the wood stove and a propane heater insert in the fireplace, as the furnace was not working, according to McCausland. The family had returned from an evening of bowling late Friday night and then started the stove, located in the first-floor living room, he said. He added that the boxes were within inches of the stove and were likely used to help ignite kindling when the wood stove fire was started.

Also found near the wood stove was a container of lighter fluid, which likely helped spread the fire once the cardboard boxes ignited, McCausland said early Monday afternoon.

Neighbors and firefighters reported not hearing any working smoke detectors in the house, he said.

State Fire Marshal Joe Thomas said combustible items should be kept 3 feet away from any wood stove and flammable liquid should never be used to start a wood stove fire.

Thomas also said families should have and practice escape plans from a house and have a central meeting spot outside to account for everyone.

“Smoke detectors, wood stove safety and having fire escape plans should be part of every Maine household to keep families safe this winter,” Thomas said.