See: Schripp T, Markewitz D, Uhde E, Salthammer T. Does e-cigarette consumption cause passive vaping? Indoor Air 2012. DOI: 10.1111/j.1600-0668.2012.00792.x.
In the study, human subjects either smoked a cigarette or used (vaped) an electronic cigarette in an experimental chamber. Concentrations of a number of volatile organic compounds were measured using gas chromatography/mass spectrometry.
Based on the chamber emissions study, 20 volatile organic compounds were identified in tobacco smoke. Of these, 6 were detected in the electronic cigarette vapor. The concentrations of these six compounds in electronic cigarette vapor ranged from 2.5% (for acetaldehyde) to 39.1% (for acetone) of the concentration in the tobacco smoke.
The exhaled air from vapers was also tested for these compounds. The only compounds detected were small amounts of nicotine and flavorings, moderate levels of glycerin, and high levels of propylene glycol.
The Rest of the Story
This study confirms that electronic cigarette use greatly reduces the user's exposure to a wide range of chemicals in tobacco smoke. The few chemicals for which exposure remains are at levels well below that of cigarette smoking.
The only compound of significant concern was formaldehyde, but its levels were between 5 and 10 times higher in tobacco smoke than in the electronic cigarette vapor. One hypothesis is that formaldehyde may result from the heating of propylene glycol.
My sense is that in the long-run, electronic cigarettes that use glycerin as an excipient may become the standard. Using glycerin would probably avoid the production of most of the volatile organic compounds detected in this study, and would also alleviate any concerns about respiratory irritation.
The exhaled vapor from electronic cigarette smokers contained mainly propylene glycol, glycerin, and small amounts of nicotine. There does not appear to be any major concern at this point regarding any dangers of exposure to "passive vaping."
The bottom line is that electronic cigarettes show great promise as an effective smoking cessation device that greatly reduces health risks for smokers and at the same time, helps protect nonsmokers by eliminating secondhand smoke.
Previous studies have demonstrated that the number of carcinogens is greatly reduced in electronic cigarettes and the levels of the only known carcinogen in the product are at trace levels. Thus, it is quite clear that electronic cigarettes greatly reduce the carcinogenic risks associated with cigarette smoking. This study documents that electronic cigarettes also greatly reduce exposure to a wide range of volatile organic compounds, making it very likely that these devices also reduce the risks of lung disease.
Based on the findings in this study, there is every reason to believe that electronic cigarettes are much safer than tobacco cigarettes and that if smokers can quit smoking via the use of these products, they are greatly improving their health.
I don't expect anti-smoking groups to alter their position based on this scientific evidence because their opposition is based on ideological and economic grounds rather than scientific ones in the first place. However, these results should help to reassure ex-smokers who have quit using electronic cigarettes that they have done themselves a great favor and reduced their health risks substantially, despite the advice from many anti-smoking organizations and researchers that they should return to cigarette smoking rather than use an "illegitimate" tool for smoking cessation.