The investigation into the chocolate factory explosion is focused on the gas pipeline

Federal safety officials are investigating the role of a natural gas pipeline in a fatal explosion at a Pennsylvania chocolate factory, the National Transportation Safety Board said Tuesday.

Friday’s powerful blast at RM Palmer Co. killed seven people, sent 10 to the hospital and damaged several other buildings in West Reading, a small town 60 miles (96 kilometers) northwest of Philadelphia, where the 75-year-old family owned the property. The company has had a factory for a long time.

The National Transportation Safety Board announced an investigation late Tuesday afternoon, calling the incident a “natural gas” explosion and fire. The agency has preliminary information from local authorities and a natural gas company that the gas line was plugged, agency spokesman Keith Holloway told The Associated Press.

Holloway said the NTSB is investigating “what caused, how and why the explosion occurred.”

Other local, state and federal investigations are ongoing.

Pennsylvania State Police said “everything is on the table” as firefighters also try to determine the origin and cause. Some workers told relatives they smelled natural gas before the explosion, but gas utility UGI said it had no reports of a gas leak.

“UGI is cooperating with authorities in their investigation of the incident at RM Palmer,” utility spokesman Joe Swope said late Tuesday. He referred further questions to the NTSB.