A sign stating efforts to reduce exposure to vapors is shown at the "C" tank farm during a media tour of the Hanford Nuclear Reservation Wednesday, July 9, 2014 near Richland, Wash. Officials said Wednesday that 12,000 air samples taken at Hanford this year after more than three dozen workers reported being sickened by chemical vapors have failed to find a cause for the problem. (AP Photo/Ted S. Warren)
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