THURSDAY, Nov. 18 (HealthDay News) -- Millions of harried travelers must still put up with unhealthy fumes from indoor smoking at one in every four major U.S. airports, a new study finds.

The analysis of smoke-free policies at large-hub airports in 2002 and 2010 found that smoking is permitted inside seven of the nation's largest airports, including three of the five busiest: Hartsfield-Jackson Atlanta International Airport, Dallas Fort Worth International Airport and Denver International Airport.

Other major airports that allow indoor smoking include: Las Vegas McCarran International Airport, Charlotte Douglas International Airport, Washington Dulles International Airport and Salt Lake City International Airport.

The study was conducted by a team at the National Center for Chronic Disease Prevention and Health Promotion, part of the U.S. Centers for Disease Control and Prevention (CDC). The researchers found that 22 percent of U.S. passenger boardings -- about 151 million embarkations annually -- still take place at the airports that permit smoking.

Instead of adopting smoke-free policies, a number of airports have installed enclosed, ventilated smoking rooms. However, complete elimination of exposure to secondhand smoke cannot be achieved by separating smokers from nonsmokers, cleaning the air and ventilating buildings, the U.S. Surgeon General concluded in 2006.

Only 100 percent smoke-free policies fully protect airport travelers and workers from secondhand smoke, the researchers said.

The study is published in the Nov. 19 issue of the CDC's journal, Morbidity and Mortality Weekly Report.

The researchers noted there is no safe level of exposure to secondhand smoke, which causes serious health problems and death. For example, secondhand smoke causes an estimated 46,000 heart disease deaths and 3,400 lung cancer deaths in the United States each year.

More information

The U.S. Environmental Protection Agency has more about secondhand smoke.