The big square box is the charcoal canister and the small one is the purge valve. The fuel vapors from the gas tank vent line go into the charcoal canister. There the charcoal absorbs moisture, and stores the fuel vapors until they are released back into the engine via the purge selenoid via signal from the pcm. I believe there may be some smog pump lines routed in that area also. Since I dont have any emissions stuff on my car, it is all removed. My ventline is hung at the back of the car near the fuel tank. If you leave this line disconnected and it is venting near the fenderwheel, you would possibly smell the vapor inside the cab of the car. Its the same thing as the ventline on motorcycles and fourwheels. If you look at the pic, you can see my gas cap ventline on the bike. I has a one way valve that wont let fuel spill out if laid over. My car doesnt have that, just a line, so if it was flipped over, fuel would leak out. I dont think its anymore dangerous than carb float bowls dumping fuel in an engine bay when they are flipped over.