CHARLESTON, W.Va. -- Both north and southbound lanes of Interstate 77 at mile marker 111 and 113 were reopened Wednesday morning following a massive gas explosion and fire Tuesday afternoon.

Workers from the state Department of Transportation worked overnight to repair the crumbling road, which melted after the massive fire ripped across the Interstate.

Overnight predictions said crews hoped to have the repairs done by this afternoon. But crews were ahead of schedule with northbound lane repairs finishing before midnight.

Road crews stopped temporarily to let the gas crew test the line and had to leave the worksite. Around 3 a.m., the northbound lanes of I-77 North between the Charleston split and mile-marker 113 were open. W.Va. 21 between Charleston and Pocatalico quickly followed.

Shortly after 7 a.m., crews had about 200 tons of asphalt left to lay on the southbound lanes and around 8 a.m., -- just in time for the morning commute - both lanes were open, according to the DOT's Twitter account.

State Transportation Secretary Paul Mattox said walking on the surface of I-77 after the blast and fire "was like walking on the cinder track back in high school." The emulsion bonding the asphalt surface together burned away, leaving a layer of loose gravel on top.

"Initially, I thought it would take at least 24 hours to get I-77 reopened, but thanks to a coordinated effort by our crews and crews from American Asphalt Paving and West Virginia Paving, we had all lanes in both directions open by 8 a.m."

The rapid repairs were made in spite of a three-hour, middle-of-the-night shutdown to allow gas crews to test repairs to the line. An 800-foot long segment of the freeway had to be milled down though its asphalt surface material to its concrete layer, and then receive a new layer of asphalt. Heat-melted guardrails were replaced, and the driving lanes were re-striped.

Four homes were destroyed and five others were damaged when the gas line exploded, shooting flames 80 to 90 feet in the air.

No one was killed in the explosion and fire. Several people were treated for smoke inhalation, either at the scene or at local hospitals. But everyone was accounted for, and no one was seriously injured in the blast.

Investigators from the National Transportation Safety Board were at the scene this morning to begin gathering physical evidence for a detailed probe of the incident.

During a briefing Tuesday night at Yeager Airport, NTSB member Robert Sumwalt described the pipeline that blew up as being a 30-inch-diameter interstate transmission line owned by NiSource subsidiary Columbia Natural Gas Transmission. Previously, local officials had said the incident involved a 20-inch pipeline.

This afternoon, in a statement issued on Twitter, the NTSB said the company had originally told agency officials it was a 30-inch line, but NTSB investigators later confirmed it was actually a 20-inch pipe.

Sumwalt also said that NiSource reported the pressure inside the pipeline at the time of the blast was 929 pounds per square inch, compared to the line's "maximum allowable" pressure of 1,000 pounds per square inch.

The NTSB is an independent government agency that investigates civil transportation accidents. The board has no regulatory or enforcement authority, but instead issues reports that detail why accidents occur and recommends changes industry and regulatory agencies could make to avoid future incidents.

"This is just the beginning of the investigation," Sumwalt told reporters.

"It could be weeks before we know the cause of the explosion," state Homeland Security and Emergency Management Director Jimmy Gianato said Wednesday morning. "The NTSB folks on the scene now are taking photos, interviewing witnesses and taking metallurgical samples that will have to be analyzed later."

Gianato said the first report of the explosion incorrectly stated that the Cedar Ridge Center nursing home had blown up, "so we were expecting a lot of casualties."

It turned out that Cedar Ridge was not damaged in the blast, though it did lose power and phone service, and had to make use of a generator and cell phones, although several homes in the vicinity were destroyed or damaged.

"It's a miracle no one happened to be home in those places when the explosion happened," Gianato said. "And with the volume of traffic that travels on the interstate, we were very fortunate that no cars were damaged on I-77 or Route 21."

Gov. Earl Ray Tomblin praised first responders, emergency medical service crews, volunteer firefighters, State Police and Kanawha County Sheriff's deputies, highway contractors and Division of Highways crews for efficiently managing the emergency.

"After this, I think we will see more inspection and testing of pipelines going on," he added.

"We're all interested in seeing what we can do to make sure something like this doesn't happen again," said Gianato.  

Following a September 2010 natural gas transmission pipeline explosion that killed 8 people in San Bruno, Calif., the National Transportation Safety Board harshly criticized the emergency response efforts of the pipeline operator, Pacific Gas and Electric Co.

NTSB investigators said in that case that the 95 minutes PG&E took to stop the flow of gas and isolate the ruptured line "was excessively long and contributed to the extent and severity of property damage and increase the life-threatening risks to the residents and emergency responders."

The agency said that the use of either automatic shutoff valves or remote control valves would have reduced the amount of time taken to stop the flow of gas in that incident.

NTSB member Robert Sumwalt said Tuesday night that the Sissonville explosion occurred at 12:41 p.m. and that the flow of gas was stopped at 1:45 p.m., 64 minutes later.

On Wednesday, Chevalier Mayes, communications manager for pipeline operator NiSource Gas Transmission and Storage, declined to describe what sort of shut-off systems the company had in place at the Sissonville pipeline.

Mayes also did not respond to questions about the age of the pipeline and for details of any recent examinations of it by the company.

"Much of the information you inquired about is being assessed as part of the ongoing investigation," Mayes said in an email message. "We'll share more details as we can."

Kanawha County Commission President Kent Carper said he is concerned about the flow of information from NiSource to local emergency responders, especially concerning potential dangers from a second gas transmission line he was told is located in the area of Tuesday's explosion.

"What would have happened if that other line had breached?" Carper said. "It looked like to me the flow of information was a little slow in coming in, but it was a chaotic scene."

Hours after the explosion, respiratory therapist Sancha Adkins was still shaky. She was heading north toward a patient's home in Ripley, a tractor-trailer behind her, when a flash alongside the highway caught her eye.

"And then I just see this whole huge ball of fire, and I'm slamming on the brakes and pulling off to the side of the road, and then the flames come across the road in front of me," she said, still breathless and nearly hysterical hours later. "I saw parts of something - I don't know what it was, a house maybe? - exploding."

A wall of flame roared across the highway about 150 feet in front of her car, she said, and she tried to back up on the shoulder. So did the truck behind her, which was able to stop without rear-ending her vehicle.

"But that wasn't fast enough for me," said Adkins, 36, of St. Albans. "I did a U-turn in the middle of the road and literally drove the wrong way on the interstate. I had my hazard lights on flashing, just trying to tell people to get out of the way."

There was oncoming traffic as she hugged the berm on the median.

"I didn't care," she said. "It wasn't as bad as that explosion."

Adkins traveled about 2 miles, got into an emergency lane and got off at the nearest exit, onto Route 21, still bound for Ripley. Then she realized she was still heading toward the flames.

"I don't think it clicked until then. I was hysterical and crying and flipping out," she said.

She tried to dial 911 three times, she said, but couldn't get the numbers right. Eventually she called her office and told them what happened.

"I'm incredibly lucky I didn't die in a fire," she said as she tried to unwind at a hair salon Tuesday evening.

Kanawha County Metro 911 Director Johnny Rutherford said Metro 911 handled more than 1,650 calls in the three hours following the 1 p.m. gas line explosion and fire. He said the high call volume triggered alarms at Frontier Communications.

Similar high call volumes following superstorm Sandy and the June 29 derecho windstorm caused 911 systems in several states to crash. However, because of upgrades and improvements to the Kanawha County system and a close working relationship with Frontier born out of previous 911 outages, Rutherford said Metro never crashed.

"Our backup systems worked, and 911 was able to keep functioning," he said.