"National Vaper’s Club, a pro–e cigarette advocacy group, published a 'risk assessment' of e-cigarette and cigarette use that concluded that 'neither vapor from e-liquids or cigarette smoke analytes posed a condition of 'significant risk' of harm to human health via the inhalation route of exposure.'77 The authors failed to detect benzo(a)pyrene in conventional cigarette smoke despite the fact that it is an established carcinogen in cigarette smoke, and their assessment of conventional cigarettes concluded that they did not pose significant risk, both of which point to fatal errors in the data, data analysis, or both. Another report15 funded by the Consumer Advocates for Smoke-free Alternatives Association and published on the Internet used occupational threshold limit values to evaluate the potential risk posed by several toxins in e-cigarettes, concluding that 'there is no evidence that vaping produces inhalable exposures to contaminants of the aerosol that would warrant health concerns by the standards that are used to ensure safety of workplaces.' Threshold limit values are an approach to assessing health effects for occupational chemical exposures that are generally much higher (often orders of magnitude higher) than levels considered acceptable for ambient or population-level exposures. Occupational exposures also do not consider exposure to sensitive subgroups such as people with medical conditions, children, and infants who might be exposed to secondhand e-cigarette emissions, most notably nicotine."

Source

Rachel Grana, Neal Benowitz and Stanton A. Glantz, "Contemporary Reviews in Cardiovascular Medicine: E-Cigarettes: A Scientific Review," Circulation (Dallas, TX: American Heart Association, May 13, 2014). 2014;129:1972-1986. doi: 10.1161/CIRCULATIONAHA.114.007667, p. 1978.
http://circ.ahajournals.org/c…
http://circ.ahajournals.org/c…