(USA TODAY) -- Don't be surprised if you see someone in an airport smoking what looks like a cigarette.
Passengers cannot use electronic cigarettes, also known as e-cigarettes, on flights. However, major U.S. airports are divided on whether or not people can use them inside the terminal.
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Currently, e-cigarettes - battery-powered devices that deliver nicotine and produce an odorless vapor - fall through loopholes in federal regulation. The Food and Drug Administration will be proposing national rules for e-cigarettes, including how they can be marketed and age restrictions for purchasing e-cigarettes.
For now, state and local laws dictate how airports govern their use indoors, according to the Airports Council International. This gray area has led to different protocols at different airports - sometimes even within the same airport.
Tampa International Airport is among the facilities that permits e-cigarette usage.
USA TODAY Network reached out to the nation's busiest airports to find out which ones allow you to "vape" inside. Ronald Reagan Washington National Airport, Las Vegas' McCarran International Airport, Minneapolis-St. Paul International Airport and Charlotte Douglas International Airport are among airports that permit the use of e-cigarettes inside. Miami International Airport has given the OK for now, but says it is reviewing its policy.
San Francisco International Airport, Chicago's airports, Philadelphia International Airport and Los Angeles International Airport treat e-cigarettes the same as tobacco cigarettes and have banned their use inside, except for in smoking-designated areas.
To make things more confusing, New York City's LaGuardia International and John F. Kennedy International airports both ban and permit e-cigarette use - depending on the terminal you're in.
The state of New York does not have specific laws banning e-cigarette use indoors, so businesses can set their own policies. The New York Port Authority oversees the airports and bans e-cigarette use in the terminals it operates, but it leases some terminals to airlines and private companies, which can have their own policies on e-cigarette use.
At LaGuardia, e-cigarette use is banned in Terminal B, operated by the New York Port Authority, but is allowed in Terminals C and D, operated by Delta Airlines . At JFK, e-cigarette use is banned in JetBlue's Terminal 5 but allowed in Delta's Terminal 2.
New York City and Chicago are considering laws to ban e-cigarette use in public spaces, treating the device the same as tobacco cigarettes. If the measure passes in New York, that means e-cigarette use will no longer be allowed in any of the airports' public spaces.
The FDA tested samples of the nicotine liquid solution vaporized by e-cigarettes and found "detectable levels of known carcinogens and toxic chemicals," according to a 2009 report from the agency.
The e-cigarette industry, however, says the product is a low-risk alternative to tobacco cigarettes and do not produce secondhand smoke.
One industry group says that banning e-cigarettes as if they were tobacco cigarettes would "wrongfully perpetuate unfounded fears, myths and common misconceptions about vaporizers," according to an e-mailed statement from the Smoke Free Alternatives Trade Association.
E-cigarette use has been "growing rapidly," according to the Centers for Disease Control. One in five smokers had tried e-cigarettes in 2011, double the number from the previous year, a CDC report found. Overall, about 6% of Americans smoked e-cigarettes in 2011, CDC said.