Washington’s indoor smoke ban – a law pioneered in Pierce County – is looking even smarter than anyone first thought.

When the ban was enacted by initiative in 2005, the case for it largely rested on the health of people who work in smoky places – bartenders, waiters and the like. They were at risk, the argument went, because they were forced to breathe the exhaust of smokers eight or more hours a day.

And so they were. But an accumulating body of evidence suggests that other nonsmokers are also placed at grave and immediate risk by shorter exposures to tobacco smoke.

The latest study – a review of heart attack statistics in Pueblo, Colo. – is stunning. Done by Colorado doctors and public health authorities, it found that heart attacks serious enough to require hospitalization fell by 41 percent in the three years after Pueblo adopted an indoor smoke ban.

In science, correlation does not equal causation. Were there other factors that drove down the rate of heart attacks? The researchers tested for this by comparing Pueblo residents with their Pueblo County neighbors outside city limits and the citizens of adjacent El Paso County.

Earlier findings had been criticized for skimpy data. This wasn’t skimpy. More than 100,000 people in Pueblo were compared to more than 600,000 people nearby. The three years of data would also have guarded against statistical flukes.

What’s going on? The U.S. Centers for Disease Control, which endorsed and published the study, concluded that even relatively small doses of tobacco smoke – “such as those received from secondhand smoke” – can heighten the risk of heart disease.

Some defenders of tobacco have countered that the researchers didn’t distinguish between smokers and nonsmokers who’d suffered heart attacks. They suggest that the numbers might have been driven down by people quitting smoking after the ban.

The fact that people experience dramatically fewer heart attacks shortly after quitting smoking is not much of an argument against smoke bans – which help smokers quit. In this case, though, the Centers for Disease control cited an earlier study that did distinguish between smokers and nonsmokers. It found that nonsmokers got two-thirds of the risk reduction from a smoke ban, which translates into a large risk increase from secondhand exposure.

People who don’t like smoke bans typically argue that adults ought to be able to make their own decisions about health and smoking. That’s true. It’s precisely why smokers should never be able to force their bad decisions on others through secondhand smoke.