Two more Hanford tank workers were taken to Kadlec Regional Medical Center Wednesday after developing symptoms believed linked to tank vapors.
Four workers also were evaluated by the Hanford medical provider, HPMC Occupational Medical Services, after reporting symptoms.
It was the second day in a row and the third day in the last two weeks that workers have reported symptoms linked to chemical vapors from the Hanford underground waste tanks. HEPA filters prevent radioactive particles from venting into the atmosphere at the tank farms, but do not capture many other nonradioactive chemicals.
Data collection and analysis are underway in the affected tank farms to understand what happened and what could be done to reduce the likelihood of future occurrences, according to Washington River Protection Solutions, the tank farm contractor. Some of the tank farms where vapors were reported are several miles apart.
The presence of chemical vapors is one of the hazards of tank farm operations, the contractor said. It takes a conservative approach to dealing with risks, including minimizing worker exposure and providing an appropriate medical response, if needed, it said.
The Herald has reported on incidents in which Hanford workers experienced symptoms related to tank farm chemical vapors since at least 1987. Changes have been made through the years to better protect workers, including alarms that sound when chemicals are detected, more industrial hygiene professionals at the tank farms and increased monitoring for chemicals with a combination of techniques.
Symptoms reported through the decades have generally included some variation of sore throats, coughing, burning eyes, headaches, skin irritation, a metallic taste in the mouth, nose bleeds or dizziness.
Watchdog groups also have reported that workers have experienced accelerated heart rates and breathing difficulties. A few workers say they have gone on long-term disability because of past exposures.
Workers generally smell ammonia, one of the chemicals in the headspace of the tanks. But a study by the previous tank farm contractor found about 1,500 chemicals in the headspace of the tanks, including mercury and benzene.
The issue came to a head in 2003, resulting in multiple studies by the state of Washington, federal organizations, independent consultants and Hanford watchdog groups.
Exposure limits that consultants considered to be safe were set and changes to venting systems were made at the tank farms.
Most of the chemical vapors are linked to work to retrieve waste from Hanford's leak-prone single-shell tanks. Certain weather conditions, such as inversions, also have been linked to increases in vapor incidents.
When waste is retrieved, a fan is used to pull air from the tanks. The air is run through HEPA filters and then sent up extended-height stacks to keep vapors away from workers and help disperse it. Air is continuously monitored.
Some of the double-shell tank farms also have extended stacks.
However, waste was not being retrieved from two single-shell tank farms where vapors were smelled this week and they did not have the extended stacks. Vapors also were smelled at adjoining double-shell tank farms, which are among those that have not had extended stacks installed.
Those with symptoms Wednesday included three workers in the T Tank Farm, which was evacuated. Two of those workers went to Kadlec and the other to HPMC.
The other three workers with symptoms, all of whom were taken to HPMC, did not work at the tank farms for Washington River Protection Solutions. They were doing work for other Hanford contractors or subcontractors near the AY and AZ Tank Farms on Tuesday when those tank farms were evacuated.
They reported symptoms Wednesday that may be related to chemical vapors, according to Washington River Protection Solutions.
Workers checked at HPMC Wednesday were cleared to return to work. The two workers taken to Kadlec were released but it was too late in the day to be also evaluated by HPMC to potentially be cleared to return to work.
Tuesday, several workers at the AY and AZ tank farms and the S Tank Farm also smelled chemical vapors, but all had been cleared to return to work by Wednesday.