Hanford officials have identified two potential sources of chemical vapor emissions after workers reported symptoms at the nuclear reservation's tank farms this week and last week.
At least 18 workers have reported symptoms linked to possible chemical vapors from tank waste, with the latest case Thursday afternoon.
Only one worker has not been cleared to return to work, because they have yet to be evaluated by the site medical provider.
Four workers were sent to Kadlec Regional Medical Center and others were was sent to the Hanford medical provider.
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Washington River Protection Solutions, the Hanford tank farm contractor, held a series of meetings with workers Thursday afternoon to discuss possible sources of the vapors and what is being done to protect people.
Hanford has 56 million gallons of radioactive and hazardous chemical waste in underground tanks. It is left from past plutonium weapons production.
The tanks vent to the atmosphere and filters prevent radioactive particles from being released. But the tanks also have at least 1,200 chemicals that have been detected and those chemicals may be released in vapors or found in waste-contaminated equipment in the tank farms.
Washington River Protection Solutions said an investigation found a cut in insulation at a pump pit in the A Tank Farm, which is near the AY and AZ Tank Farms where symptoms have been reported on at least two days.
The worker reporting symptoms Thursday also was in the area of the complex of tanks that includes the A, AY, AZ and AX tanks.
The cut was sealed with foam and the area was re-evaluated. Instruments no longer detected elevated levels of potential vapor-causing compounds in the area, according to Washington River Protection Solutions.
In the S Tank Farm, where two workers were sent to the hospital Tuesday, the investigation has focused on liquid in old, unused equipment that had been staged for disposal.
The workers had been cutting plastic wrapped around a block covering the equipment when they experienced symptoms.
The area around the old equipment has been cordoned off as a vapor control zone and the liquid is being sampled and analyzed to determine if it could be a potential source of emissions.
An investigation at the T Tank Farm, where workers reported smelling vapors Wednesday, has found no detectable measurements of vapor-causing compounds, according to Washington River Protection Solutions.
But investigations to identify other potential sources of vapors are continuing, according to the contractor.
The symptoms of all workers exposed recently have not been made public.
But tank farm workers exposed to vapors at Hanford have generally reported symptoms that include sore throats, headaches, coughing, burning eyes, nose bleeds, a metallic taste, dizziness or an accelerated heart rate.
Workers fear that exposure could cause long-term health problems.
Hanford Challenge, a Seattle-based watchdog group, believes that past exposures have led to cases of toxic encephalopathy, neurological damage and long-term chemical sensitivity.
Tank vapors have been an issue at least since the end of the Cold War, with Hanford officials taking steps through the years to better protect workers.
However, Hanford Challenge said not enough is being done.
Thursday it called for Washington River Protection Solutions and the Department of Energy to support workers who have experienced symptoms, to step up monitoring of chemical vapors and to take more protective measures.
Washington River Protection Solutions said it is encouraging workers to wear respirators, if they believe it is necessary.
It has kept worker exposure to chemical vapors far below national occupational standards, it said. The contractor's standards at the tank farms are generally 10 percent of national occupational standards, said Jerry Holloway, spokesman for the contractor.
When a previous tank farm contractor identified more than 1,000 chemicals that could be present in tank vapors, it found that many did not have occupational standards. A consulting group was used to help determine safe limits.
Washington River Protection Solutions has an Industrial Hygiene Technical Panel that includes management and employee members. It meets regularly to address chemical vapor issues and concerns, including identifying potential hazards and developing controls.
The panel also will be addressing the recent chemical vapor issues, Holloway said.
The risk of chemical vapors at the tank farm cannot be completely eliminated, but the contractor is continuing to look for ways to reduce risks to workers, it said in a statement.
-- Annette Cary: 582-1533; email@example.com; Twitter: @HanfordNews