Georgia Power has until mid-January to provide state utility regulators with a detailed explanation of how an underground electrical fire darkened Atlanta's Hartsfield-Jackson International Airport for 11 hours on Dec. 17, sparking a disruptive domino effect across the international air traffic system.

The Georgia Public Safety Commission posed 20 questions to determine the exact sequence of events that led up to the blaze, which Georgia Power says may have originated with the failure of utility-owned switch gear, located in an underground electrical facility. Because the fire occurred adjacent to redundant circuit cables and switching mechanisms, the airport's electrical system was unable to switch to alternative power feeds.

A joint investigation by Atlanta firefighters and federal agencies found no evidence of unauthorized activity associated with the incident.

Along with questioning Georgia Power about future preventative measures, the commission also is asking whether a microgrid could have minimized the fire's effects. Several major U.S. surface transit systems currently are developing or investigating alternative power supply and storage systems to preserve operations in the event of a major grid disruption; yet, only a handful of small airports have or are considering incorporating microgrids.

Georgia Power's owner, Southern Co., completed a $461-million purchase of Wake Forest, N.C.-based microgrid technology specialist PowerSecure in May 2016. A commission spokesperson says Georgia Power's responses will be made public, unless those responses include trade secrets. After reviewing the responses, agency staff will determine whether to make recommendations to the commissioners or request additional information.