In our business we're talking to fleets all the time about the pros and cons of converting their vehicles to run on LPG auto gas. Typically with courier companies in certain municipalities, they have to do deliveries and go underground to do that. One of the barriers they have to deal with is that they can't take these propane-powered vehicles underground.
With a propane tank, if it is filled to 80% it's totally safe to go into such environments. As long as the tank is not being overfilled there should be no venting issues with the product. There should be no reason for it to expand and escape from the tank. So as long as people are using the auto-stop filler valves that have been available since the mid-1990s, there should be no reason from a safety standpoint why these vehicles cannot go in underground parkades.