Scientific studies in recent years have warned about the health impact from second-hand smoke and linked it to a wide array of ailments including heart disease, lung cancer and other respiratory ailments, and breast cancer.

"I think there is no question that this puts California way ahead," said John Froines, chairman of the Air Resources Board's Scientific Review Panel.

"To actually have the major air pollution agency in the state of California to list ETS (environmental tobacco smoke) as a toxic air contaminant is going to have immense impact, we think, in terms of public education around other states," he said. "It will clearly lead to regulatory changes within the state."

The panel's 2005 study found that about 16 percent of all Californians smoked, but 56 percent of adults and 64 percent of adolescents were exposed to second-hand smoke.

"Because the diseases are common and ETS exposure is frequent and widespread, the overall impact can be quite large," the study found.

California's Office of Environmental Health Hazard Assessment estimates that as many as 5,500 non-smoking Californians die annually of heart disease related to second- hand smoke and as many as 1,100 die from lung cancer caused by second-hand smoke.

GROWING TOBACCO BANS

The decision in the California state capital kicks off a process that will likely take two or three years as officials study ways to reduce exposure to second-hand smoke.

A spokeswoman for tobacco giant Philip Morris USA, a unit of Altria Group Inc., declined to comment.

In 1994, California became the first US state to bar smoking in the workplace, and then followed up with bans on smoking in restaurants and bars. Other American cities and states have since adopted similar prohibitions.

Several California cities have enacted wider bans, such as San Francisco, which now prohibits smoking in city parks, and Los Angeles, which bars smoking at piers and beaches.

Some health experts say the ultimate impact of California's decision to classify second-hand smoke as a toxin could reach beyond the United States.

"It is important because it has included important new findings, new scientific information that will not only help California policymakers but will help those across the United States address this issue," said Paul Knepprath of the American Lung Association of California.

"And, as I think some board members mentioned, this impact on the international community could be very helpful."