[rohrmann]

Now, this I'm not sure of, but propane IS heavier than air, but Mercaptan might not be heavier, so I would be diligent about making sure you don't have even a slight leak. If you haven't replaced the pigtails going to your cylinders in a while, that would be a place to check. Also, there is an O-ring in the opening of the valve where you connect the pigtail to the cylinder valve that could have a crack that could cause a leak. The soap test should show a leak.