On July 11, 1979, a partial meltdown occurred at the Three Mile Island nuclear power plant in Pennsylvania, leading to widespread public fear about the safety of nuclear energy. The incident was caused by a combination of mechanical failure and operator error, releasing a small amount of radioactive gas. While the accident did not result in immediate deaths, it sparked a significant debate about the risks of nuclear power. It led to major changes in nuclear regulations and a halt to the construction of new nuclear power plants in the U.S. The disaster is often cited as the most serious accident in the history of U.S. commercial nuclear power.