All of the weaponised gas (and gas-like) compounds that I know of are primarily based on chemical reactions, or, as a better way to put it, the attributes of the gas itself. They are used to blind, harm, or kill, among other peculiar methods of weaponisation.
But what about using air pressure? Would it be possible to raise the pressure in a house, so that the air, trying to escape, blasts out the windows? If so, how would this be done? If not, how might something equivalent be accomplished?
There are no restrictions on technology, but size needs to be kept minimal. This should be just as useful as a frag grenade, in the sense that it is deadly but small enough to be handheld. I get a funny feeling that someone will come up with something that demands FTL technology. So yes, FTL is allowed.
I was thinking something along the lines of a small canister that has the capability to compress air (a lot of it), when it is activated. A soldier could crack it out, take some readily available air, make it into a solid (pretty far fetched) and then release when ready. The only problem being... It wouldn't work. So...