Multiple radiation alarms are being investigated at NASA's Goddard Space Flight Center in Greenbelt, Md.
But radiation was later ruled out as a cause.
A smoke alarm in the radiation lab apparently caused the radiation alarms to sound, according to Prince George's County Fire. The smoke alarm is under investigation. No smoke is visible.
Firefighters stood by while NASA officials and Prince George's County hazmat teams discussed the course of action.
Stay with News4 and NBCWashington.com for updates as they become available.