They fall over all the time. I used to do this exact thing. We would load/unload semi-truck trailers from the loading dock, and bring them into and out of the gas filling rooms. We used this technique because it was more efficient.

When I first started there, the first thing my boss did was to take two cylinders like he was going to start rolling them, and then let them fall forward with a loud clang! He did this to show that it wasn’t going to do anything by itself, and that trying to catch them was going to hurt you more. Cylinders fell over all of the time. They are pretty stout, and are thoroughly inspected every time they are refilled, and are either hydrotested or ultrasonically tested routinely (depending on the type of cylinder).

The only time they are really going to give you grief is when they don’t have the cap affixed.