No worries...I used to be around someone who smoked A LOT, and I'm in the Navy, so I'm always getting tagged to pee in cups (and I've never popped positive)...but from what I understand, the levels of THC released in secondhand smoke aren't enough to cause you to pop on a whiz quiz. If you were in a car, or a room with lots of smokers, to the point of nearly being hotboxed, I'd say you might have a problem, but I think it's safe to say you're fine.