You really need more than just an enclosed space. You need an enclosed space and a large amount of pot smoking going on. It is possible to get second hand exposure but it would require smoking 10 blunts or more (just an example) in a small minivan or air tight closet. Remember, exhaled smoke contains very little THC as it is almost instantly absorded by the lungs. Casual second hand smoke isn't going to show up and that is what most second hand smoke is, casual and insignificant.