They ARE being very careful..
A helicopter from the agency charged with U.S. nuclear security will be flying low over the Washington, DC, area to measure background radiation levels in the coming weeks.
The National Nuclear Security Administration (NNSA) said on Dec. 26 that it would be flying a helicopter over portions of Washington between Dec. 27, 2012 and Jan. 11, 2013 to measure naturally-occurring radiation levels in the area.
The agency has conducted similar overflights in other cities, including Baltimore and San Francisco, earlier in 2012. It explained that the measurement of naturally-occurring radiation to establish baseline levels is a normal part of security and emergency preparedness. It said it was making the public aware of the upcoming flights so citizens who see the low-flying aircraft aren’t alarmed.