How It Works: An Electronic CigaretteSince electronic cigarettes hit the market in 2007 yearly sales have reached $1 billion in the U.S. Although they re popular it s still unclear how safe they are. Last year a study from an international group of scientists showed that the toxins in e-cigarette vapor are 9 to 450 times lower than in tobacco smoke. The Food and Drug Administration is still determining its regulatory stance. It s sponsoring more research while sorting out its position.When the e-cigarette is active an indicator light glows like a tobacco ember.Some versions have a pressure sensor that detects the airflow of an inhalation. The sensor then turns on the battery which triggers the heating element. Other e-cigarettes are turned on and off with a button.A slim lithium-ion battery usually rechargeable provides the power. An average e-cigarette has about 300 puffs per charge.  Electricity passes through a resistant material �usually metal or ceramic �which produces heat. Once the heating element reaches approximately 150 °F it vaporizes about 0.005 milliliters of the nicotine liquid into a mist. Each hit has roughly 90 percent of the nicotine found  in a tobacco-cigarette puff.A viscous fluid made from propylene glycol vegetable glycerin or a mixture of both contains about 1 percent nicotine and flavoring such as menthol fruit or classic tobacco.A flexible tip sometimes made of silicone evokes the feel of a real cigarette.Continue reading about How It Works: a Wiffle ball a surgical snakebot and moreThis article originally appeared in the April 2014 issue of Popular Science.