A natural gas leak is the preliminary suspect in the explosion and collapse of three apartments in the 85-year-old La Rosa building complex at 102-104 South Lotus Ave. Monday morning. Six people were hurt in the collapse, at least one of them seriously. Thirteen families have been temporarily displaced.

While police and fire investigators are still working to determine the cause of the explosion, the massive blast and no subsequent fire supports preliminary assessments that the explosion was caused by natural gas.

“Right now we’ve got to shift through all this rubble to get at what happened here,” said Fire Department spokesman Larry Langford.

Residents of the building reported smelling gas just prior to the explosion, which occurred around 7:20 a.m. The blast, which witnesses described as either a “loud boom,” or “like thunder,” blew the aluminum replacement windows on the east wall of the building 100 to 150 feet across Lotus Avenue into a vacant lot.

A 12- or 13-year-old boy described only as “T.J.” but later identified as Tyrell Lee, was walking by the building at the moment, according to witness Monique Johnson, who said she lives across the street from the destroyed building.

“I heard a boom, and I saw him flying,” Johnson said of the boy. “Then two little girls came out from the second floor, covered in debris.”

Johnson said T.J. appeared to have a broken arm and a head injury.

“He had a big old knot on his head,” said Johnson, “and a broken arm.” T.J., she said, was conscious, but didn’t want assistance.

“He wouldn’t let anyone help him. He was calling for his mother.”

Also injured in the blast and collapse were Keisha Manning, 25, Antonio Forrest, 26, Kyra Forrest, 4, and Khali Forrest, 1.

The building was purchased less than three weeks ago by Tom Viere, according to 29th Ward Alderman Isaac Carothers, in whose ward the building is located. Viere arrived on the scene a few minutes after 9 a.m. and began conferring with fire and city officials.

The scene was a bit surreal. Both the east and north walls had collapsed, opening up the inside structure to public view like an oversized dollhouse. The hardwood floor of the third-floor living room where Kyra and Khali Forrest had been sitting at the time of the explosion slanted downward at a curved and cracked angle, coated with dust. The couch the two girls had been sitting on rested on the corner edge of the floor. A television set sat upright above a large displaced cast iron radiator.

Officials quickly determined that the three apartments directly affected by the blast were structurally unsound, and ordered them torn down. Tow trucks were called in to remove adjacent parked cars, and a large backhoe was then brought in to perform the demolition.

Carother’s chief of staff Brenda Smith said Wednesday that the 29th Ward office was awaiting word from the Chicago building department as to when the complex’s residents would be allowed to re-enter their apartments to recover personal belongings.

At least five of the 13 families left homeless by the collapse have approached the 29th Ward office for help in the aftermath of the incident.

“We’ve been dealing with the families, trying to get them assistance with relocation, clothing and other needs,” said Smith.