Is second-hand vapor from e-cigarettes dangerous?

Researchers and committees have set out to answer exactly this question.

A study performed inside a vape shop found that air exposure to hazardous chemicals and nicotine is minimal to non-existent.

Another 2014 study, published in BioMed Central, found that the current research data indicates 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."

In short it seems there is no need worry about secondhand vapor as it does not pose a threat. There are however regulations with regards to where you can and cannot vape. If you're an avid vaper be sure to inquire about the US bans and worldwide regulations on vaping.