Cleburne, TX- A natural gas main leak is to blame for a house explosion that injured five people, a city official said Wednesday.

The leak migrated into the sewer system and caused an accumulation of gas in the house, which erupted Tuesday when someone inside lit a cigarette, Cleburne City Manager Chester Nolen said.

“As far as we know, they are serious injuries, but not life-threatening,” he said.

Misty Sanderson, 17, was not seriously hurt in the explosion, but her parents and grandparents were.

The five injured were taken to Parkland Memorial Hospital. On Wednesday afternoon, Joyce Sanderson, 44, was in critical condition; Steve Sanderson, 49, was in serious condition; Hazel Pawlik, 64, was in critical condition; David Pawlik, 66, was in fair condition. A 9-year-old girl was also hospitalized, but a Parkland spokeswoman said she could not release information on the minor.

Officials say all the family members are expected to survive.

In the ground near the home you could see a corroded gas line. The leak from the line forced gas into the house. The subsequent explosion blew bricks off the walls and pushed a fireball through the roof.

Nolen said that the roof lifted off the brick home and the walls were moved several inches off the foundation during the explosion, which left a large hole in the roof. The house did not have gas service.

“It’s not a usual occurrence and most of the time you’ll smell it. In the concentrations that it takes to cause an explosion, most of the time you’ll know it well before any explosion occurs,” Nolen said.

About 30 nearby homes were evacuated as officials tried to determine the cause of the explosion. Nolen said that most of the residents were allowed back home Wednesday morning and the remaining residents were expected to be able to return shortly.

Cleburne is about 30 miles south of Fort Worth.