The National Transportation Safety Board investigates gas line explosions. Here's a listing from the NTSB database of gas line explosions in Pennsylvania. Details of the explosions were not available for the years before 1990.

Feb. 9, 2011 in Allentown: A UGI natural gas explosion killed William Hall, 79; his wife Beatrice Hall, 74; Ofelia A. Ben, 69; Ben's granddaughter, Katherine Cruz, 16; and Katherine's 4-month-old son, Matthew Vega. The explosion was at 13th and Allen streets.March 5, 2008 in Plum Borough, Allegheny County: One man killed and a 4-year-old child was injured; two homes were destroyed and 11 others were damaged. The blast caused $100,000 damage and loss. The lines were owned by Dominion Peoples Natural Gas Co. Officials determined the probable cause to be excavation damage to a 2-inch gas line.Aug. 21, 2004 in Dubois, Clearfield County: A natural gas pipeline explosion owned by the National Fuel Gas Distribution Corporation leveled a home, causing two deaths and an estimated $800,000 in damage. The probable cause was determined to be the fracture of a defective butt-fusion joint and the failure of the National Fuel Gas Distribution Corporation to have an adequate program to inspect butt-fusion joints and replace those joints not meeting its inspection criteria.June 9,1994 in Allentown: A UGI natural gas pipeline explosion and fire at a retirement home killed one person, injured 66 others and caused more than $5 million in property damage. Authorities determined the probable cause to be that a 2-inch-diameter steel gas service line that had been exposed during excavation separated at a compression coupling about five feet from the wall of the home.The escaping gas flowed underground, passed through openings in the building foundation, migrated to other floors and exploded.Aug. 29, 1990 in Allentown: One person was killed and nine others, including two firefighters, were injured when an explosion destroyed two row houses on North Fifth Street. Authorities determined the probable cause to be water leaking from a cracked municipal water line that eroded the soil beneath a UGI cast iron gas main, which fractured due to the weight of the soil and sidewalk above it. The gas leaked into the basement of 423 N. Fifth St., where it ignited, according to the NTSB.Dec. 16, 1988 in Stroudsburg: A gas explosion destroyed a church. Authorities determined a probable cause to be a leak in a Stroudsburg Gas Co. line.Feb. 22, 1985 in Sharpsville, Mercer County: A National Fuel Gas Co. explosion killed two people and injured a firefighter.July 20, 1977 in Ruff Creek, Greene County: A Consolidated Gas Supply propane pipeline explosion.Jan. 25, 1977 in Williamsport, Lycoming County: A Pennsylvania Gas & Water Co. natural gas pipeline explosion destroyed a house.Aug. 8, 1976 in Allentown: A UGI natural gas explosion and fire killed two firefighters and injured a third.Feb. 21, 1973 in Coopersburg: A UGI gas explosion killed five people and injured 22 others.Nov. 17, 1971 in Pittsburgh: An Equitable Gas Co. explosion.