WASHINGTON » Eight members of the U.S. Senate are calling on the Food and Drug Administration to examine new research suggesting that some electronic cigarettes can produce dangerous carcinogens similar to those from traditional cigarettes.

In a letter sent Thursday, the Democratic lawmakers say that the FDA should work to protect e- cigarette users and those nearby from cancer-causing vapors apparently produced by high-powered nicotine devices, known as tank systems.

Electronic cigarettes mainly consist of a battery, heating coil and a tank that holds flavored liquid nicotine. As users puff on the e-cigarette, the battery heats the coil and the liquid is turned into a vapor that is inhaled like smoke from a traditional cigarette. Tank systems are generally larger e-cigarettes — about the size of an electronic toothbrush — that can hold more nicotine and an extended battery supply.

Studies first reported by The New York Times suggest that these devices get hot enough to produce toxic chemicals like formaldehyde, a carcinogen also found in traditional cigarettes.

E-cigarette proponents have argued that the devices are a safer alternative to cigarettes because they do not produce the smoke and tar caused by burning tobacco. But the new research by scientists at the Roswell Park Cancer Institute challenges that reasoning, at least for some products. The Buffalo, New York-based center’s study is scheduled for publication later this month in the Nicotine and Tobacco Research journal, according to the Times.

The findings also raise questions about the potential hazards of e-cigarettes for non-users who inadvertently inhale their vapors. New York City, Chicago and Los Angeles have all recently instituted bans on the use of e-cigarettes in certain indoor areas and public places.

Last month the FDA announced it would begin regulating the emerging e-cigarette field. But the senators point out that the FDA’s proposal focuses mainly on e-cigarette ingredients, rather than the vapors they produce.

"We simply cannot afford to lag behind in our complete understanding of the health consequences to the user and bystander of these and other advanced nicotine delivery products," states the letter. It was signed by Sens. Edward J. Markey, D-Mass., Sherrod Brown, D-Ohio, Barbara Boxer, D-Calif., Jeff Merkley, D-Ore., Jack Reed, D-Conn., Richard Blumenthal, D-Conn., Tom Harkin, D-Iowa, and Dick Durbin, D-Ill.

An FDA spokeswoman said in a statement that the agency is also funding research into the safety of e-cigarette vapor, including one of the studies referenced by the senators.

"Where the science does not exist, we are able to fund the research to answer key questions related to e-cigarette safety and consumer behavior. In fact, FDA is funding dozens of studies that will help answer those questions, including four studies alone that will focus on the contents of e-cigarette vapor," said Jennifer Haliski in an emailed statement.

The FDA is now taking public comments on its proposal, which treads fairly lightly on the $2 billion e-cigarette market. The FDA’s plan would ban e-cigarette sales to anyone under 18, add warning labels and require FDA approval for new products. It does not include measures favored by many anti-smoking advocates, such as a ban on TV advertising and fruit- or candy-flavored e-cigarettes.

Scientists haven’t completed much research on whether e-cigarettes actually help smokers kick the habit or simply serve as a gateway to paper-and-tobacco cigarettes. The government is pouring millions into research to supplement independent and company studies on the health risks of e-cigarettes and other new tobacco products.