Athletic 35-year-old men who have never touched cigarettes are not supposed to come down with a debilitating lung disease usually linked to smoking.

But Seth Ellingsworth of West Richland, Washington, says he got sick in an instant last year, when he briefly inhaled a strange odor at his job at the nearby Hanford Nuclear Site.

"I started having breathing problems," said Ellingsworth, "and it hasn't gone away since."

The father of four, who has reactive airway disease and is now unable to work, wore a nebulizer mask and gasped for air as he showed NBC News all the medicines he's forced to take. "This is a corticosteroid. This is a pill I take, it's Zafirlukast. This is prednisone. This is a bronchodilator."

Seventy years ago, the Hanford Site produced plutonium for America's nuclear arsenal. Today, it's run by the Department of Energy through its contractor, Washington River Protection Solutions. The contractor is managing a $110 billion cleanup of 56 million gallons of chemical and nuclear waste, stored in 177 underground tanks — a task that's expected to last the next 50 years.

Seth Ellingsworth says he became sick as soon as he inhaled bad-smelling fumes at Washington's Hanford Nuclear Site, where he worked. Seth Ellingsworth

But the tanks are leaking, and the vapors they emit contain toxic and radioactive chemicals known to cause cancer as well as brain and lung damage. Just this year, 61 workers have been exposed, and some nuclear experts have called Hanford "the most toxic place in America" and "an underground Chernobyl waiting to happen."

The DOE has acknowledged in nearly 20 studies conducted over the past 24 years that there is a safety risk to workers at Hanford. Just two years ago, a report found toxins in the air "far exceeding occupational limits" and a "causal link" between vapor exposure and lung and brain damage. The DOE has also said that the site "cannot effectively control" dangers and gives workers "no warning."

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But critics say the DOE still isn't doing enough to act on its own findings, and continues to put workers at risk.

Local neuropsychologist Brian Campbell says he has evaluated 29 people at Hanford with both respiratory and cognitive symptoms, including "some of the worst cases of dementia that I've seen in young people, which we do not anticipate."

Dr. Campbell said the DOE doesn't want to acknowledge the injuries. "More likely than not," said Campbell, "I think it's caused by the exposure they had at Hanford."

Nuclear reactors line the riverbank at the Hanford Site along the Columbia River in January 1960. The N Reactor is in the foreground, with the twin KE and KW Reactors in the immediate background. The historic B Reactor, the world's first plutonium production reactor, is visible in the distance. United States Department of Energy

When NBC News put out a call for current and former Hanford workers who believe they were exposed to toxic materials, more than 20 volunteered to talk to us. Eleven of them sat down with NBC News for a group interview.

Diana Gegg was one of several former workers who said they have dementia: "I have shaking on the right side of my body."

Lonny Poteat said he had been diagnosed with "pretty bad" nerve damage. "Sometimes the pain gets so great," said Poteat, "I just pass out."

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Mario Diaz said he was losing his memory and struggling to breathe, and became emotional when he said he's no longer able to do things with his family.

"The worst part is showing up for work out there and getting pasted because they didn't tell us," said Diaz. "They weren't forthright in sharing what they know."

The workers told us that "over and over," the Department of Energy and the contractor on site told them the readings for harmful materials were safe.

"We're told daily that it's safe," said a man who currently works at Hanford. "[That] there's nothing to worry about."

Ronan Farrow with current and former workers from the Hanford Nuclear Site. NBC News

"They're a bunch of liars," said a female employee.

Former workers also said that in the past they were almost never allowed to opt for protective gear, like the supplied air tanks recommended by many experts.

"They wouldn't let you have it," alleged a former worker.

Several told us they were discouraged from seeking safety equipment, and threatened with losing work if they insisted.

The DOE says it has no tolerance for retaliation.

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The Hanford Challenge, a local watchdog group, says that at least three deaths have a documented link to exposure at Hanford, including Gary Sall's.

Sall died in 2011 after descending into dementia, which was diagnosed as "work-related."

Some Washington state officials are now intervening, including Lt. Gov. Cyrus Habib, who has pledged to investigate and called the federal government's response "an absolute scandal."

"When you think about the risk not only to workers but also to our water supply," Habib told NBC News, "it's like a Stephen King novel. This is something that I think everyone in the country should be thinking about."

Attorney General Bob Ferguson is taking an even more unusual step — suing the federal government.

Said Ferguson, "They've known for decades. It's been going on year after year, report after report.

Ferguson said he considered the federal government's lack of action "unforgivable."

"And to be candid, they have to live with themselves on that," said Ferguson. "I ask the question all the time, 'How many more workers have to get sick at Hanford before they do something about it? How many?' Please ask them. I really want to know."

NBC News asked a DOE official that very question during a visit to Hanford. The DOE granted us rare access to the highly restricted site, and an interview with Deputy Assistant Secretary Mark Whitney.

Whitney, who has since left the DOE for the private sector, said that all Hanford workers who have been referred to medical evaluation to date have been returned to work.

NBC noted that many workers who have not returned to work are seriously, even terminally ill, and asked Whitney if the DOE maintains that these illnesses are not related to on-the-job exposures.

"I wish we had a more complete understanding of those circumstances," said Whitney. "A lot of effort the last couple years has gone into strengthening our efforts to deal with the potential vapor exposure issue."

NBC then showed Whitney a copy of Diana Gegg's medical assessment, in which doctors say her serious, possibly terminal illnesses are a direct result of her exposure at Hanford, and asked him for comment.

Said Whitney, "I'm not a medical professional and can't provide a qualified medical opinion."

Whitney says the DOE is "strengthening communication" with Hanford workers, and in 2016 invested $50 million in improving air monitoring.

At Hanford, however, a subcontractor who was monitoring the air next to a set of waste tanks refused to tell NBC News what kind of readings he was getting.

"Sorry, but I'm not allowed to discuss that," said the subcontractor.

Whitney said the DOE has taken more than 170,000 measurements of the breathing zones in Hanford's tank farms, and never found measurements higher than the permitted occupational exposure limits.

NBC, however, has documents showing DOE readings from Hanford in 2009 that are far in excess of occupational limits. Mercury was measured at 473 percent above limits, and ammonia was measured at 1800 percent above limits — and workers were not told.

"I'm not aware of what workers were told or were not or those readings," said Whitney. "Potentially those measurements were taken at the top of a 20 or 40-foot stack where workers would not be."

But a DOE study from 2014 found a significant risk of dangerous exposure at that distance from the source of vapor. "Clearly, almost 30 percent of this concentration … might by highly irritating even under very brief exposures occurring over 30 feet from the source."

Susannah Frame, investigative reporter at Seattle NBC affiliate KING, says the risk goes beyond workers at the site, and includes the risk that a tank could explode and contaminate a large area. That risk was originally raised by a government nuclear board.

Said Frame, "If you care about people that are doing the work of this country that is needed so that we don't have a nuclear disaster, you should care about Hanford. "

"Our lives don't matter," said Seth Ellingsworth. "Our health does not matter. We are simply a business decision. It costs more money to protect us than to fight us, to deal with us being sick."

Washington River Protection Solutions, the contractor that runs Hanford for the DOE, has now reached an agreement with workers' unions to provide air tanks to all workers. Experts told NBC News that the masks can help — but that they can also be withdrawn by the government at any time. They also say it doesn't solve the broader safety problems underscored by 24 years of DOE studies about the risks of working at Hanford.