More than 48 hours after the deadly explosion in Oak Cliff, federal investigators and Atmos crews remained on site. The National Transportation Safety Board (NTSB) sent a team of eight investigators to Dallas. The NTSB said its investigation will focus on three areas: human factors, the pipeline system and the operating environment. Geoff Henley, an attorney representing the owner of the Clyde apartments, told NBC 5 the property was in escrow an…