Information acquired from HowStuffWorks
Workers at Area 51 have had to endure difficult conditions since the earliest days of the facility. In the 1950s, when the focus of the base was testing the U-2 spy plane, the CIA had to cease operations and evacuate the facility due to nearby nuclear testing on the neighboring Nevada test site. Sometimes the AEC would announce tests ahead of schedule to allow nearby residents time to evacuate if they felt it was necessary, but other times the tests would remain unannounced. The results from these tests could be seen from towns 100 miles away. People in Las Vegas would often organize trips to nearby peaks and picnic in view of mushroom clouds.
In 1957, one such test called HOOD was part of an overall program called Operation Plumbob, which was designed to see if damaged nuclear bombs emitted harmful levels of radioactivity. The AEC detonated a 74-kiloton nuclear device 1,500 feet over Area 9 of the NTS. This was the most powerful airburst ever detonated over the continental United States. The AEC did not announce the test ahead of time, though they did tell Area 51 to evacuate beforehand. The resulting blast caused some minor damage at Area 51 – mostly some broken windows and doors. Radiation was a much bigger concern, and, in fact, the soil in Area 51 has absorbed a lot of radiation over years of nuclear tests.