ATLANTA (AP) -- Construction workers, miners and food service workers top the list of occupations that smoke the most, according to a new government report. Experts say it might have as much to do with lower education levels as the jobs themselves.

“There may be other characteristics that are clustering in these industries,” said Dr. Tim McAfee, director of the Office on Smoking and Health at the Centers for Disease Control and Prevention.

Traits linked to higher smoking rates and seen in employees in these industries include being younger, having fewer years of education and making less money.

Also, some people who work outdoors are less likely to face the kind of indoor smoking bans seen in white-collar workplaces like schools, hospitals and office buildings, McAfee said.

The CDC study found 19.6 percent of working adults smoke, but as many as 30 percent in the mining, construction and food service industries smoke. Librarians and teachers smoked the least, at less than 9 percent.

For decades, the biggest smokers by profession have been roofers, drywall installers, brick and stone masons and other workers in construction trades. But health officials have warned construction workers may be at elevated risk from smoking, especially if they are exposed to asbestos. Studies have shown that people who work with asbestos are more likely to develop lung cancer if they also smoke.

Smoking also can pose extra danger for miners, who might ignite methane gas with matches or cigarette lighters. Federal officials say that since 1977, four major mine explosions have been blamed on smoking that combined killed 24 miners.

The CDC study is based on in-person interviews of more than 113,000 working adults in the years 2004 through 2010.