The comparisons to Chernobyl can be a little overhyped. Where the latter was a complete explosion of the reactor and the release of significant amounts of radioactive material downwind, the Three Mile Island explosion was a reactor coolant failure and a contained meltdown. The reactor was rendered inoperable, true, but unlike in the case of Chernobyl, nobody died, and negligible amounts of radiation leaked out. Three Mile island remains, however, America’s worst nuclear incident.

On this day, March 28, in 1979, at 4:00 a.m. something caused the water pumps to the reactor to stop working, causing temperature in the reactor core to reach dangerous levels. Instead of pumping coolant in, a series of mechanical malfunctions and human actions based on incomplete information pumped the coolant out, which made the meltdown inevitable.

A lot of lessons were rightly learned from the incident: safety measures were improved, training re-focused, and instrument readings were changed to lessen the chance for confusion. No serious threat emerged to the public – extensive studies showed the max radiation dosage anyone near the plant could have been exposed to is about one-sixth the dosage of a chest X-ray, and cumulative exposure would have been about the same as natural radiation exposure from rocks and dirt outside.