My first thought is that we get hold of gas masks.

[Not strictly true! Her first-first thought was torching as much of that as possible ahead of time, but that seems like it's not much of a good idea.]

However, I expect we don't just have those lying around. Plus, I dunno how trustworthy they'd be. If they're old enough, they might even be dangerous to use depending on what's happened to the internal filters.