It began with a brief but terrible bump in the night and quickly grew into the worst commercial nuclear accident in U.S. history. At the Three Mile Island power plant near Harrisburg, Pa., a balky valve malfunctioned, setting off an intricate chain of mechanical and human failures. In the control room of the plant’s Unit II, warning lights flashed and an electronic alarm rang. Craig Faust, 32, and Ed Frederick, 29, working the night shift, studied the alarms and meters as the plant veered toward a state of emergency. They kept their heads, pushed and pulled as many as 50 buttons and levers in fifteen seconds and the reactor shut down. “What we saw we understood and we controlled,” Frederick said. But it wasn’t enough. Read how one TMI worker escaped the disaster alive.