Then-Gov. Richard Thornburgh advised pregnant women and preschool children within five miles of the Susquehanna River plant to leave after the March 28, 1979, TMI accident. Tens of thousands more responded.
Emergency sirens blared and massive traffic jams snarled area roadways through farmlands near the state Capitol amid fears the Unit 2 reactor could unleash a massive amount of radiation into the river or the atmosphere.
"People just left, and they left not knowing if they would return, or what provisions to take with them," said Eric Epstein, chairman of TMI Alert, a safe energy group that monitors Three Mile Island and two other nuclear plants in Pennsylvania.
"People were running from something they couldn't see," said Epstein, who was away at college at the time.
Conflicting news accounts and widespread uncertainty prevailed as residents in the south-central Pennsylvania countryside crushed banks with withdrawals and overwhelmed long-distance phone lines. A third of the state's 22,000 employees in Harrisburg failed to show up for work in the immediate aftermath.
The TMI Unit 2 had been operating for only three months when errors on the part of the plant operators turned a routine equipment failure at about 4 a.m. into a partial meltdown of the plant's core and a release of radioactive elements.
A pump failure on the non-nuclear side of the operation was compounded by a series of mechanical failures and human errors that resulted in too little water coolant being used to control the temperature of the reactor's uranium fuel. A molten radioactive mass very nearly burned through the 8-inch-thick steel pressure vessel before plant workers restored the flow of water coolant, bringing down the fuel temperature.
Two days later, on March 30, officials detected an uncontrolled release of radiation from the plant, prompting the evacuation. Later, they learned plant operators had planned the release to ease pressure within the system. Two days of worrying that a hydrogen bubble inside the plant might explode followed.
An angry Lt. Gov. William Scranton III accused the plant owners - General Public Utilities Corp. - of issuing conflicting information.
The TMI accident is classified as the country's worst commercial nuclear power plant accident ever; the U.S. Nuclear Regulatory Commission didn't receive an application for a plant license for almost three decades after that.
In 1984, the plant operator, a GPU subsidiary, pleaded guilty in federal court to using inaccurate test methods, manipulating the test results, destroying records, and not filing proper notice that the plant's cooling system had excessive leaks.
In the years following, more than 2,000 people who feared they were harmed by radiation leaking from Three Mile Island sued over the accident, saying exposure to radiation caused leukemia, birth defects and other health problems. In 1996, U.S. District Court Judge Sylvia Rambo in Harrisburg threw out all the damage claims, saying plaintiffs couldn't muster the evidence necessary to support their cases.
Today, Pennsylvania is home to five nuclear plants with a total of nine nuclear reactors, or units. Three Mile Island's Unit 2 is mothballed, while Unit 1 continues to operate.
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Robert Houser, now 62 and a resident of Virginia Beach, Va., was then a volunteer firefighter in the borough of Steelton, about 10 miles from the plant. He was dispatched to go door-to-door with leaflets, advising residents of the danger and possibility they'd be asked to flee.
"Some people cursed you out for disturbing them, some people were just as scared as you," Houser recalled.
Houser had no choice but to stay with his wife and two kids. He didn't have much money and all of his relatives lived in the shadow of the plant, he said, so he had nowhere to go.
"Go where? How long? Am I ever going to be able come back?" Houser said. "These were all things that were going through your mind back then."
His current wife, Lorraine, 62, was also living near TMI. She and her then-husband hastened to leave with her mother, their young daughter, and their pets. They rose early the morning of March 31, threw suitcases into their two cars and headed 75 miles to the east to her aunt's farm in Limeport, Pa.
Lorraine Houser doesn't recall any hysteria among the evacuees or being afraid herself. She said she didn't know how to explain the events to her daughter.
"You didn't want to say, 'Hey it might blow up, we've got to get out of here,"' she said.
Middletown Mayor Robert Reid was also mayor then, his little town just three miles from the TMI cooling towers built on a sliver of island in the Susquehanna. He stayed behind as about a third of the populace of about 10,000 fled.
The borough had no emergency response plan back then and that has haunted him ever since. While Unit 2 has never been restarted, Three Mile Island's adjacent Unit 1 remains in operation. "There's not a week that goes by that my coordinator and I don't sit down and talk about our evacuation plan and our disaster plan," said Reid, 78.
"Yes indeed-y, it's not going to catch me napping like it did in 1979."
All of Pennsylvania's municipal nuclear emergency plans are reviewed annually and tested every two years, said Henry Tamanini, chief of the Pennsylvania Emergency Management Agency's technological hazards division.
Among the details: An engineering firm produces an estimated evacuation time that takes into account road capacity, population, weather conditions and other factors.
Thornburgh said this week that he was startled in 1979 to learn that two counties near TMI, on opposite sides of the river, each had evacuation plans that called for their residents to cross the same bridge over the Susquehanna - straight into the oncoming paths of the other's evacuees.
He and his advisers, he said, scrambled to respond to TMI on the fly. The evacuation question loomed over their internal discussions, along with the knowledge that large-scale evacuations raise safety issues of their own, he said.
"You get people who are out on the road when they shouldn't be, or driving a speed they shouldn't be," Thornburgh said. "It's not a risk-free undertaking."
Epstein was critical of the state's pre-1979 emergency planning, saying it did not include the cities of York, Lancaster and Harrisburg, all within 25 miles of TMI.
He said plans directed evacuees onto impractical routes, assumed farmers would leave their animals behind, did not make sufficient provision for the very young and the sick and established relocation centers too close to the nuclear facility.
"It was uneven," Epstein said. "When you issue a precautionary evacuation for a limited population you have to assume the entire population will leave, and that was not the assumption."
Nowadays, plans for evacuating people from the immediate vicinity of nuclear facilities, developed by local officials and the state and federal emergency management agencies, are the result of decades of work. The authority to order evacuations is governed by state and local law - in some states, such as Pennsylvania, the governor may decide, while in others, local jurisdictions may act.
Officials must tell the public what routes to take, establish the locations of shelters and distribute potassium iodide tablets to protect human thyroid glands from radiation. The Federal Emergency Management Agency said in 2005 that more than 4.8 million Americans lived within 10 miles of a nuclear power plant. Those who lived through Three Mile Island, or have worked to improve emergency readiness in its aftermath, are watching raptly as events unfold in Japan.
"You should plan for an accident on a Friday night during a snowstorm when there's a Penn State home game scheduled for Saturday - which was what we thought the Japanese had done," Epstein said.
"I don't know that anybody anticipated a three-headed Hydra threat like they have."
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