Almost one-third of workers in mining, construction, and the accommodation and food service industries smoke, compared with about 20 percent of the general U.S. adult population, according to a new survey by the Centers for Disease Control and Prevention.

USA Today reports only about 9 percent of teachers and librarians smoke.

Smoking rates among specific occupations may have as much to do with workers’ education levels as with the jobs themselves, according to the article. Higher smoking rates were associated with being younger, having fewer years of education, and earning less. People who work outdoors may also be more likely to smoke because they aren’t subject to indoor smoking bans, noted Dr. Tim McAfee, Director of the Office on Smoking and Health at the Centers for Disease Control and Prevention.

Smoking can be especially dangerous for construction workers if they are exposed to asbestos, the article notes. Research has shown people who work with asbestos are more likely to develop lung cancer if they are smokers. Smoking is also a particular hazard for miners, who could ignite methane gas with cigarette lighters or matches.