"Second Hand" exposure to e-cig pg virtually nil

[Lessifer]

While not a peer reviewed study, here is the presentation that was given at the recent FDA workshop on biomarkers by Celerion. Their results show that bystanders showed 5,000 times less concentration of pg from e-cigs than those who were actually using the vaporizer, almost undetectable amounts. The same was found for nicotine.
https://celerion.com/wordpress/wp-content/uploads/2015/01/Celerion_2014-TSRC_Propylene-Glycol.pdf