 In September 1953, about 650 people attended the first Trinity Site open house. Visitors to a Trinity Site open house are allowed to see the ground zero and McDonald Ranch House areas. More than seventy years after the test, residual radiation at the site is about ten times higher than normal background radiation in the area. The amount of radioactive exposure received during a one-hour visit to the site is about half of the total radiation exposure which a U.S. adult receives on an average day from natural and medical sources.
