After power outage at Atlanta's airport, questions linger about what occurred

Federal agents say they are actively investigating the cause and have ruled nothing out, but have no proof it was intentional or terror-related. However, the incident also highlighted what terror experts say is an already vulnerable area of concern -- transportation infrastructure.

As operations at Hartsfield-Jackson Atlanta International Airport crawl back to normal, questions linger about what occurred. The area of concern is a frayed line that may have led to the destructive fire.

"There's a focus on infrastructure and transportation as it's related to economy," says expert Anthony Lemieux.

But he says while not impossible, attacking an onsite electrical station is unlikely.

"There are so many layers of nested security that it makes that much more difficult," says Lemieux. "For a human actor with bad intent to cause this kind of harm, that suggest a different level of planning...sophistication."

But the incident does shine a light on the need to double back and doubly secure each key infrastructure site at a major target like Atlanta's airport. CBS46 questioned airport officials about security at the underground power site. Is there a guard present? Are there cameras?

Atlanta Fire Chief Joel Baker said Tuesday that no foul play was involved in the fire. Baker's complete statement, sent from the mayor's office, is provided below:

"The Atlanta Fire Rescue Department (AFRD), in partnership with the Atlanta Police Department, Bureau of Alcohol, Tobacco and Firearms (ATF) and the FBI Joint Terrorism Task Force (FBI-JTFF) has concluded the preliminary investigation into the cause of Sunday's fire which led to the power outage at Hartsfield-Jackson Atlanta International Airport.

AFRD with our federal and local partners have determined that there is no evidence of foul play at this stage of the investigation. There is no information to suggest there was an insider threat or any connection to terrorism.

Smoke from the fire traveled throughout multiple terminals and areas within the airport. AFRD firefighters investigated every location where smoke was seen, and identified a single point of origin: The fire was caused by an electrical failure inside of a switchgear box located in the long below-grade tunnel which runs beneath the airport concourses. A subsequent intense arc flash ignited surrounding insulation and other combustibles inside the box."