Robert Sumwalt, a member of the National Transportation Safety Board, said Wednesday that he was told the tank cars were empty.
An undated Google satellite image of the yard shows five of seven tracks occupied by railcars, almost all of them tankers. A string of 16 tank cars occupied the westernmost track, which on Tuesday night was ripped up by the Amtrak locomotive and several of the train's coaches.
John Enright, a Conrail spokesman, said he could not comment on the type of freight typically parked in tank cars at the Frankford yard. "Just because they're tank cars doesn't mean they contain crude oil," he said.
While public attention lately has been fixed on the plethora of oil-train accidents linked to the domestic shale boom - there have been five fiery derailments this year alone - none have involved passenger trains.
Freight trains typically don't use Amtrak's rails. But cargo often moves on tracks adjacent to passenger lines, in the same right of way.
Joseph Martin, a Drexel University civil engineering professor, was involved with designing a crash wall in Albany, N.Y., to separate a freight line from local passenger tracks.
"The idea of a freight train rolling over on a passenger line and crushing everybody has already occurred to people," he said.
Fred Millar, a hazardous materials consultant and rail safety advocate, believes dangerous cargo needs to use different routes than those that carry passenger traffic. "We need to ask Amtrak: Do they not have a risk analysis that takes into consideration nearby hazards?" he said.
The Frankford Junction facility is a small yard that Conrail uses primarily to sort railcars for delivery to local customers, said Enright. Conrail is jointly owned by CSX and Norfolk Southern, which share the use of its assets.
The local customers include a Delaware River ethanol terminal and several chemical plants, though there are no nearby crude-oil facilities. Enright said the railcars that occupy Frankford Junction could just as well be empty or contain nonvolatile commodities, such as corn syrup.
"Our view is, it's sort of a what-if story," he said.
Not all crude-oil rail accidents were initiated by oil trains.
One spectacular oil-train accident, a 2013 explosion in Casselton, N.D., was caused by a train carrying soybeans, which derailed and "fouled" an adjacent tracks. A crude-oil train traveling the opposite direction crashed into an errant soybean hopper; 18 derailed oil tankers caught fire, forcing the evacuation of 1,400 residents.