HANFORD — Workers are raising the height of exhaust stacks that emit fumes to ventilate Hanford tanks that hold radioactive and hazardous chemical wastes.
It's a step to better protect workers who have reported that breathing in the chemical vapors gave them headaches, scratchy throats
and watery eyes. Officials say the change also will help them prepare to resume retrieving waste from the underground tanks.
Waste retrieval stopped near the beginning of summer when Washington River Protection Solutions hit an obstruction hidden in the sludge in Tank C-104, one of 142 single-shell tanks at Hanford that still have radioactive waste.
Work is under way to pump waste from leak-prone tanks into sturdier double-shell tanks until the vitrification plant is operating to treat the waste for disposal.
The Department of Energy contractor has been working to prepare to start emptying another tank, Tank C-111, and expects to be ready around Labor Day.
Work will resume after the improvements to the vapor-protection system. It had been halted twice and then resumed during retrieval from Tank C-104 because workers were concerned about the vapors.
The C Tank Farm -- which includes 16 underground tanks -- is in bowl that's about 15 feet below grade. The ventilation stacks have stood 17 feet high, which put the control trailer at the same level as the stacks.
Under certain weather conditions -- including light winds from the right direction or stagnant air -- workers could smell the vapors as waste was disturbed during retrieval.
Work under way now will raise the height of the portable stacks being used at Tank C-111 and Tank C-104 by an additional 23 feet. Preparations are being made to return to emptying Tank C-104, once work on Tank C-111 is complete.
Modeling of the change in vapor dispersion showed that even in the most unfavorable weather conditions, there should be more than an 80 percent reduction in the concentration of chemicals in the air that workers breathe, said Kent Smith, deputy manager of single-shell tank retrieval for Washington River Protection Solutions.
The vapors that vent into the atmosphere include 1,800 chemicals, with 58 known to be present in quantities that could rise to harmful levels. They include nitrous oxide, mercury, ammonia and benzene.
All 58 are well below 10 percent of the occupational exposure limit in the air that workers breathe, Smith said. Workers are required to wear respirators or other protection in certain areas where vapors may be present at higher levels.
But even with the stacks extended to 40 feet high, workers likely still will smell some chemical vapors, Smith said. Some chemicals, such as ammonia, can be smelled at levels far below occupational exposure limits, he said.
Other options were considered to reduce vapor exposure, but raising the stacks seemed the quickest change to achieve a major reduction in vapor exposure, Smith said.
Other options include routing the stack emissions to be released in a more remote location.
Additional steps also have been taken, such as increasing monitoring with a combination of techniques that include hand-held monitoring by industrial hygiene technicians and monitors worn on workers' lapels. Alarms have been installed that sound when chemicals are detected at extremely low levels.
* Annette Cary: 509-582-1533; acary@tricityherald.com; more Hanford news at hanfordnews.com.
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