Hanford workers may soon go back into part of the tank farms without wearing supplied air respirators to protect them from vapors emitted from underground tanks of nuclear waste.

"CH2M Hill has engaged in a very rigorous process to evaluate impacts to human health," said Russell Shearer, the Department of Energy's acting assistant secretary for environment, safety and health.

He visited Hanford's tank farms Wednesday to recognize workers in the double-shell tank farm operation for improving safety performance.

Two years ago CH2M Hill Hanford Group, which operates the tank farms for DOE, began requiring workers to wear supplied air respirators when they worked near the underground tanks. The tanks hold 53 million gallons of radioactive and hazardous chemical waste from the past production of plutonium for the nation's nuclear weapons program.

Workers feared breathing chemical vapors that vented into the air from the tanks was making them ill. State and national reports later concluded that too little was known about what was in the tanks to be sure that workers were not being harmed.

"We've done a lot of work in the last couple years," said Mark Spears, CH2M Hill chief executive.

The contractor sampled the head space of all the tanks to determine that 1,500 chemicals were present. Many had no established occupational exposure limits.

CH2M Hill brought in experts with national reputations to help set safe exposure limits for the chemicals, Spears said.

With that knowledge, CH2M Hill believes workers who remain at least five feet away from the vents should be exposed to amounts significantly below harmful levels.

The contractor expects soon to begin allowing workers into the A Tank Farms - certain fields of tanks named with A prefixes - without supplied air respirators.

However, supplied air in tanks that workers carry on their backs will remain optional.

"We expect when we start off, a fair number of people will want respirators," Spears said.

The respirators do have drawbacks. They're heavy, they can add to heat stress in summer and the masks can limit vision.

Having workers on supplied air contributed to what Spears called one of the worst safety records in DOE's cleanup complex when he spoke at a Nuclear Cleanup Caucus Briefing held by Rep. Doc Hastings, R-Wash., in Washington, D.C., earlier this month.

But CH2M Hill has been able to turn that record around to be awarded DOE Voluntary Protection Program "star status" in its double-shell tank department. The Waste Feed Operations department operates 28 double-shell tanks that are collecting waste from 149 older, leak-prone tanks and holding them until the waste can be treated for disposal.

"Star status for Waste Feed Operations? Who would have thought of that two years ago?" asked Dave Molnaa, president of the Hanford Atomic Metal Trades Council, at a ceremony Wednesday to honor the 400 workers in the department.

Workers have won the designation despite the numerous health hazards at the tank farms, lack of appropriate funding and staff reductions, he said.

Several speakers credited letting workers take more leadership and responsibility in the program's safety culture for a sharply reduced rate of slips, trips and soft-tissue injuries.

Management teams have come and gone over the years, but the work force has been constant, Spears said.

Workers have come up with changes such as a stand to help put on and take off heavy protective equipment using ergonomically correct movements. They also developed a simple device to tip 40-pound bags of protective clothing forward, eliminating the need for workers to pick them up.

In addition, management became focused on improving safety, Spears said.

In the first half of 2005, 34 cases were recorded of workers unable to do their regular jobs because of work-related injuries. That dropped to six in the second half of the year and none so far this year at CH2M Hill.

"It's a remarkable accomplishment over a short period of time," Shearer said.

DOE has recognized 25 programs across the nation with star status for excellence in safety and health. The final assessment that led to the award included interviews with 70 percent of the Waste Feed Operations workers, observations of work and reviews of safety documents and records.

Shearer has been acting assistant secretary for environment, safety and health since earlier this month when John Shaw resigned.