Adult e-cigarette users comfortable with the unknown health risks of “vaping” should feel free to fire up in their homes, their vehicles and in outdoor spaces where vapor from the devices quickly disperses.

What e-cig users shouldn’t be allowed is do is decide that e-cigs’ potential benefits trump the risks for other Minnesotans, such as the kid with asthma at the nearby restaurant table, the pregnant woman two seats down at the theater or the nearby elderly gent with a heart condition.

The vapor created by e-cigs when the liquid in them is heated, which can be smelled by those nearby, is likely safer than traditional tobacco smoke. But that’s little comfort when cigarette smoke is so dangerous to begin with and when researchers have found that e-cig aerosol can contain metal and silicate particles in addition to nicotine. E-cigs’ smokelike swirl typically comes from propylene glycol, a common cosmetics additive also used in airplane de-icing fluid. Claims that it’s just water vapor are bunk.

What the risks are from inhaling this vapor either first or secondhand is unclear at best. The e-cig market is moving at warp speed, with sales now estimated at more than $500 million a year. Medical researchers are unfortunately playing catch-up. So are regulators. The manufacture of the liquid “juice” converted by these devices into vapor has had no federal oversight to assure safety and purity.

Until the risks are better understood and managed, Minnesota lawmakers should heed the advice of the state’s leading medical experts and ban e-cigs indoors in public spaces and businesses in the way traditional tobacco is prohibited now under the state’s amended Clean Indoor Air Act.

Legislation that would do just that, in addition to a ban on e-cig use in schools and criminalizing e-cig sales to minors, has made promising progress in the Minnesota Senate. But the indoor ban was irresponsibly stripped from the House version of the bill during a committee hearing, despite the concerns of lead author Rep. Laurie Halvorson, DFL-Eagan.

Halvorson and DFLer Sen. Kathy Sheran, who is carrying that chamber’s legislation, have clearly put in time on this issue and are familiar with both the research and the cautions voiced by leading medical experts such as Minnesota Health Commissioner Dr. Ed Ehlinger and the Mayo Clinic’s Dr. Richard Hurt. The Minnesota Medical Association supports an indoor ban on e-cigs.

Unfortunately, the ban’s opponents, who disappointingly now include Gov. Mark Dayton, have not done the basic homework needed for informed policymaking. Had opponents bothered to get informed, they would have realized that their two main arguments simply don’t hold up.

The first is the oft-repeated claim that vapor is nothing to worry about. The March 2013 study that found metal and silicate particles in the vapor also concluded that “Many of the elements identified in [e-cig] aerosol are known to cause respiratory distress and disease.” This isn’t definitive proof of the vapor’s potential risks, but it certainly raises troubling questions.

Recent studies also refute the argument that e-cig users should vape away wherever they want because these devices are so valuable in helping them quit tobacco. Research published this week in JAMA Internal Medicine raised doubts about e-cigs’ efficacy for kicking the tobacco habit. A recent study in the journal Lancet concluded that the devices were not significantly more effective than a placebo. Another point: Not everyone wanting to vape is trying to quit smoking. E-cigs may be creating new nicotine addicts.

The available research on e-cigs makes Dayton’s position hard to understand. On one hand, he wants scientific proof that medical marijuana works, but he’s fine with e-cigs when the benefits are unproven, the risks are unknown and the state’s medical providers are urging caution.

Given e-cigs’ dubious stop-smoking value and the unknown risks, the common-sense approach is to ban indoor use until their safety and value are proven. The predictable whining about the “nanny state” is utter nonsense. Under the Senate bill, users have every right to be e-cig guinea pigs in their personal space. But they shouldn’t be able to force other Minnesotans to do the same.