AEP-Southwestern Electric Power Co. staff continued Monday evening to try to find the cause of a massive power failure that affected about 85,000 of its customers Sunday throughout Northeast Texas, spokeswoman Carey Sullivan said.

“We have not determined the cause,” Sullivan said about 5:30 p.m. Monday. “We continue to work with our team in (AEP) headquarters in Columbus, Ohio, to analyze the data we’ve downloaded from our equipment in the field.”

Sullivan, based at SWEPCO headquarters in Shreveport, said dozens of people are looking into the cause of the outage, which started around 4:30 p.m. Sunday with power fully restored within about five hours.

The Rusk County Office of Emergency Management said Sunday that the outage was caused by what it called an “incident” at a SWEPCO substation near the Eastman plant. However, SWEPCO said later Sunday that it could not confirm that.

The power failure affected businesses and homes, prompting Longview’s largest industrial employer, Eastman Chemical Co., to shut down.

Operations at the Eastman plant had not been restored completely as of Monday afternoon, Eastman spokeswoman Kristin Parker said in a statement.

Parker, who is based at corporate headquarters in Kingsport, Tennessee, said the plant is working through safety protocols to bring all units back online over the next few days. No one was injured.

“SWEPCO’s power outage forced us to have an unplanned shutdown, and our equipment responded as designed under these circumstances,” Parker said. “During the shutdown, the flares safely controlled process materials but may have emitted certain materials in excess of the levels that require us to provide the (Texas Commission on Environmental Quality) and the National Response Center notice.”

She said it is a normal procedure to contact regulatory agencies when flaring during a shutdown.

“We do not believe those releases had any impact on employees at our site, nearby neighbors or the surrounding community,” she said.

Texas Commission on Environmental Quality spokesman Andrew Keese said in an email Monday afternoon that Eastman Chemical reported emissions of benzene; 1,3-Butadiene; xylene; toluene; nitrogen oxide; and acetaldehyde through the National Response Center.

He said the TCEQ reviewed its air emissions event report database and did not have a record of receiving the emissions report as of 2 p.m. Monday.

Keese said estimated emissions might be revised in the final notification that is due in two weeks.

“After the final notifications are received, TCEQ will conduct an investigation of the reported emissions events to determine compliance with applicable rules, permit provisions, notification and reporting requirements,” he said. “TCEQ will continue to monitor this situation.”

During the flaring Sunday at Eastman, a grass fire broke out on site, Parker said. The fire was small, and an on-site fire crew contained and extinguished it.

Parker said SWEPCO told the plant it is still working to identify the causes of the outage, and the plant is remaining in communication with the power company.

An event like Sunday’s shutdown has not happened in several years, she said.

“A sitewide interruption is a rare event,” she said. “This would be classified as an interruption, not an outage at the plant.”

The power failure also prompted authorities to activate the Emergency Operations Center between 4:30 and 5 p.m. Sunday at the direction of Longview Police Chief Mike Bishop, Longview Fire Chief J.P. Steelman and Gregg County Emergency Management Coordinator Mark Moore, Gregg County Sheriff Maxey Cerliano said. The center remained open until about 10 p.m.

Cerliano said the decision to keep the center open “was based on the large amount of citizens that were affected by the power outage, along with all of the associated issues that went with that,” but not because of concerns about Eastman.

“There is an emergency plan that’s in effect, and Eastman has an emergency plan that’s in effect that the city of Longview and Gregg County are very familiar with and, in fact, train with Eastman on,” Cerliano said. “The procedures that were in place were followed (Sunday), and there were no concerns about a release or of that manner.”

In addition to affecting SWEPCO customers, the power failure also caused more than 12,000 members of the Upshur Rural Electric Cooperative to lose power at its peak, said Chad Wade, the co-op’s dispatch supervisor. The co-op serves a 10-county region with about 46,000 meters.

The co-op buys electricity from several sources, but SWEPCO delivers it to Upshur Rural through SWEPCO’s transmission lines, said Tony McCullough, the co-op’s marketing and communication manager.

The co-op received its first reports of a power outage from 4:40 to 5 p.m., “when all the lights started to blink,” McCullough said.

The co-op responded by turning off its metering point at about 5:30 p.m. where it receives the electricity from SWEPCO near Big Sandy, Wade said. That, in turn, shut down the co-op’s substations.

Wade and McCullough said the intent was to prevent damage from low voltage to the co-op’s systems and to air conditioners and appliances of its members.

“Once we shut down, we contacted them,” Wade said, referring to SWEPCO. “They allowed us X amounts of megawatts. We call it ‘step restoring.’”

Service was fully restored at around 9:30 p.m., McCullough said.