Families in an Oklahoma City neighborhood were left in shock Thursday morning.

Families in a quiet Oklahoma City neighborhood were left in shock Thursday morning after the home of a family of four exploded, killing a teenage child.

“They are a sweet family — just the nicest people — and I’m heartbroken for them,” Patti Woodard, a neighbor of the family, told ABC News affiliate KOCO.

Investigators say that the cause of the explosion was a propane log lighter inside their fireplace that was not up to code.

“The log lighters are illegal,” said Nicholas Nadeau, an investigator with Oklahoma’s Liquefied Petroleum Gas Administration. “They do not have a pilot safety shut off. So in case of an outage of flame, you’re just going to accumulate propane vapor inside a residence that will lead to an explosion.”

“The dad kept saying he plugged in the coffee pot and he was electrocuted and the house blew up. He kept saying that like a thousand times,” neighbor Patty Wommer told KOCO. “His clothes were tattered all over. The explosion almost blew the clothes off him.”

Nadeau said the explosion could have been sparked by the father trying to plug in his coffee machine or even turning on a light.

Wommer said the father walked out of the house calling for his children. He was taken to the hospital in serious condition along with the rest of the family, who needed to be treated for burns.

Benny Fulkerson, district chief public information officer for the Oklahoma City Fire Department, told KOCO that responding to the blast has been emotional. Dozens of firefighters arrived to the scene to find debris scattered everywhere.

“Obviously you don’t ever want to see a child lost in this. It’s tough,” he said. “We’re here to help when we can. Our hearts go out to the family, for sure.”