There was an article years ago about the second-hand smoke issue. It was published in a trucking industry magazine, and the USDOT wanted the question answered regarding truckers who swore they were exposed to it against their will but didn't consume. They were successfully using this defense to get out of cannabis-related fines and points against their licenses.

According to the article, there was a quite comprehensive study done - including people who were put into small rooms filled with cannabis smoke and put on a treadmill for half an hour.

The USDOT conclusions were that NO TRACES OF CANNABIS could be found in the blood of the people who were exposed to even large amounts of cannabis smoke under physical stress; therefore, the defense that truckers had been using for decades was then struck down and ANY cannabis found in their system, from that day forward, was considered CONSUMPTION and could not be considered an accidental consequence of being around people consuming cannabis.