On this day in labor history, the year was 1979.
That was the day The Three Mile Island Unit 2 reactor partially melted down near Middleton, Pennsylvania.
A combination of equipment failure and human error has long been attributed as the cause of the meltdown.
An initial overheating and reactor shut down had occurred.
But a pressure valve remained stuck open, allowing coolant to escape.
Design flaws in control equipment failed to indicate the position of the valve.
Workers then mistook the increased pressure as a result of excessive coolant.
They shut off the emergency water system that could have cooled the core.
Fears of radiation release and hydrogen bubbles led to voluntary evacuations that included over 140,000 residents.
Authorities assured the public that the partial meltdown had been contained.
President Carter convened a commission to investigate the causes.
It concluded that while the operators took inappropriate actions, the training they received was inadequate as were the procedures they were required to follow.
Plant designers, Babcock and Wilcox were held responsible for poor design.
The company failed to notify operators of repeated valve failure and a previous near duplicate of the potential catastrophe at the Davis-Besse plant.
Metropolitan Edison, General Public Utilities and the NRC were also held responsible for poor quality control, poor maintenance, communication lapses and poor training.
Fears regarding public health and safety intensified, fueling health studies of those exposed and the anti-nuclear power movement.
The aftermath brought about sweeping changes involving emergency response planning, reactor operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operations.
It also caused the NRC to tighten and heighten its regulatory oversight. All of these changes significantly enhanced U.S. reactor safety.