The long-term effects of smoke exposure on wildland firefighters, such as those battling blazes in Washington, are not clear. Scientists say more study is needed.

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During some of the worst of the wildfires in North Central Washington, a monitor near Omak, Okanogan County, reported air quality as “hazardous”, with particle levels more than 20 times those recorded on the worst days last year.

“It’s just been this thick layer of fog,” said Lauri Jones, a community-health director in Okanogan County, of the smoke late last month. “My voice is a little raspy. Oh, it’s horrible air quality.”

When air quality reaches “hazardous” levels, “Everyone should stay indoors, do only light activities and keep the windows closed if it is not too hot,” the state Department of Ecology advises. That’s good advice, especially for at-risk groups, but for firefighters battling the Okanogan complex blaze, it’s not an option.

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“I hear it when I wake up in the morning, guys are coughing,” said Rick Isaacson, a fire-information officer. “But that doesn’t slow them down.”

Firefighters are trained to recognize the dangerous short-term effects of smoke exposure caused by carbon monoxide and tiny particles absorbed into the lungs.

But smoke exposure’s long-term effects are less clear, and scientists say more study is needed.

Carbon monoxide can cause throbbing headaches, nausea and confusion, which leads to “a safety issue if you’re not making a credible decisions,” said Roger Ottmar, a research forester at the Pacific Wildland Fire Sciences Laboratory in Seattle.

But those symptoms can be quickly remedied, said Tim Reinhart, an industrial hygienist who has studied the issue.

If “you end up with nausea and a throbbing headache, it’s reversible,” he said. “You just need to get to clean air.”

Firefighters can wear devices called dosimeters that detect high levels of carbon monoxide, but their bodies also signal smoke’s danger.

Irritants from the smoke like formaldehyde sting firefighters’ eyes and cause their noses to run. “You have some senses to detect you probably shouldn’t be in this stuff for long,” said Ottmar.

Tiny particles, some of which can be a fraction of the width of a human hair, can cause sore throats, interrupt breathing and make firefighters susceptible to “camp crud,” colds and viruses that attack immune systems busy warding off smoke’s effects.

George Broyles, a U.S. Forest Service researcher who has studied smoke and chemical-exposure levels with working firefighters, said studies show firefighters recover full lung function after the season’s over. But beyond a season, scientists are largely in the dark.

“When you start looking at particulate matter and you start being overexposed to it day after day, month after month in a firefighter career, we do not know a lot of information about long-term exposure. That’s where additional research is needed,” Ottmar said.

“Anecdotally, we haven’t seen shortened life spans or bad health as they age. That may be a function of their high level of fitness to begin with — the job attracts industrial athletes,” said Reinhardt.

The Occupational Safety and Health Administration (OSHA) sets limits on workers’ exposure to chemicals. Reinhardt said firefighters are most likely exposed to levels of chemicals above the public-health standard, but below OSHA limits.

Broyles’ research found firefighters exceed OSHA standards for carbon monoxide exposure about 5.6 percent of the time.

But the occupational limits assume exposure over an eight-hour day worked throughout a career, not during the course of a 14-hour workday firefighters sometimes endure. Those limits also don’t factor in the mix of chemicals firefighters might be taking in.

“It’s nothing like a standard work environment,” said Broyles, of wildland firefighting.

Long-term studies of wildland firefighters are particularly challenging.

“It’s very hard to do studies at the fires because of these chaotic conditions. They’re sporadic, you can’t plan for them (wildfires),” said Michael Kleinman, a toxicologist at the University of California, Irvine, studying air quality.

Many firefighters are seasonal. Some work their way through college as firefighters before going on to other careers. That makes studying a group over the long haul difficult.

Kleinman has been studying laboratory mice with implanted heart and blood-pressure monitors.

He said wildfire-smoke exposure to mice was linked to “aggressive” drops in blood pressure and may cause “hardening of the arteries and development of plaque in the arteries.”

Kleinman said more study is needed to understand what might be causing those results.

“It would not be surprising if there would be long-term consequences for wildland firefighters by breathing this smoke,” Kleinman said.

For now, researchers are encouraging wildland firefighters to minimize smoke exposure with common-sense methods like periodically rotating off fire lines for fresh air, limiting high-exposure mop-up duty (such as stirring a dying campfire) and using closed-cab bulldozers with air-filtration systems.

“We know we have smoke exposure, at times, that is more than we want to see. It may take a number of years before we can answer the research questions, but we can educate the workforce,” Reinhardt said.