Actually, if the tire is filled with a liquid, such as CaCl, the tire is MUCH safer to work with, as the danger is in how much the contents of the assembly can expand. At say, 150 psi, air compresses a lot, so when it is uncontrollably released, it expands to it's original volume quickly. Liquids on the other hand, don't compress very much, so when they are released uncontrollably, it just squirts out a little bit and that's it.
Now, there is still some air in the tire, so there is still some danger. And for working on it, I would put that valve at the bottom, as if it does happen to fail, it will be liquid coming out, which can't go through the failure point as quickly as a gas can.
Edit: fixed "still some air in the TIRE".
And to clarify, having the weak spot at the bottom if/when it fails, a bunch of fluid will come squirting out at 150 psi (so you'd want a blanket or something to control where it goes) until the air inside the tire expands to it's uncompressed volume. It's safer because the liquid can't go through the opening as quickly as air can, so it happens over a much longer period of time.