Drexel University engineer explains possible cause of I-95 collapse in Philadelphia

PHILADELPHIA (WPVI) -- As we grapple with the aftermath of the Interstate 95 collapse in Philadelphia, local engineers are dissecting this incident from every angle.

A structural engineering expert at Drexel University says there's already a big takeaway from this.

It has to do with exposed steel underneath the bridge, and an apparent lack of fireproofing.

Dr. Abi Aghayere says it appears this span collapsed because of the exact spot where the fire erupted under the bridge.

"The thought that came to my mind is that it's a freak accident," Dr. Aghayere explains. "The question is: Should there have been fireproofing provided for this bridge section or any bridge section over a roadway?"

Dr. Aghayere explains that when a fire occurs on top of a bridge, the steel is protected by the concrete roadway.

RELATED: 'The road's falling': Philly drivers capture video of heavy flames before I-95 collapse

The fire was so big it had overtaken both northbound and southbound lanes on the highway, witness Lisa Taormino, who was commuting southbound on I-95 about 20 minutes before it collapsed, told ABC News.

In this case, the steel underneath the bridge melted because it was exposed, as is seen in a picture from Google Maps from just before the incident.

To protect the beams, he says something called intumescent paint would help.

"It's a fireproofing material," Dr. Aghayere explains. "It's expensive, but helpful when you have the bridge crossing over a road. My suggestion is that, at least with bridges or overpasses, the steel beams in that section of the bridge should be coated with intumescent paint."

Right now, there's no direct mandate to fireproof steel girders underneath bridges.

RELATED: 'I have no idea what is on fire': Dispatch audio reveals moments before I-95 collapse in Philly

"We need this off-ramp shutdown. I have no idea what is on fire," an officer can be heard saying over the radio.