Cheap surplus gas masks have always been on the market in large quantities (mostly Soviet/Eastern Bloc). But as of late, I've noticed many more Western surplus gas masks, especially from Finland, in the $15-20 range.

I have no idea why and how but I see these masks marketed as protection against the swine flu plus all the usual bio/chemical/nuclear threats. It seems people are buying them in serious quantities and even attempt to use them in hazardous environments.

From what I've seen, the filters are usually from the 1970's so with a shelf life of about 10 years they're already way past their prime. I'm no expert but I've always been taught old gas mask filters past their useful life should never be used and as the chemicals in them break down, aside from not working as they're supposed to, they might in fact pose a health hazard.

I don't know whether any of it depends on proper storage but I've been under the impression that all gas mask filters have a very definite shelf life and once past, must be disposed of. So what is going on with all the people getting old gas masks these days? Do the filters really last longer than the date says? Are there any real differences between Eastern Bloc and Western filters? Or is everyone buying surplus gas masks just wasting money on obsolete, potentially lethal gear?