Different things require different gasmasks.. for example, military gasmasks stop particles (like smoke, dust, fall out, virusses) and chemical agents like mustard gas, fosgene and chlorine gas..
BUT, they don't help against things like gasses from solvents.. (biggest threat as civilian; trucktanker with chemicals that crashes etc)
In the Netherlands we have a large company that supplies all sorts of things for companies.. from pencils to full protection suits, from fire extenguishers to pallets..
www.overtoom.nl
They probably have such an company in germany (or more then one)
Gasmasks are pretty expensive. I would prefer a civil above a military, because they have a larger "window" (monoscreen instead of 2 glasses) and a lare variety of filters. And note that filters only work about 4 hours (depends on the sort of stuff you are breathing).
I would get an mask with one filter for solvents, and one for chemicals. As something happens (alarm) simply turn on the radio or look it up on the internet, and view what's going on, and use the filter.
They are pretty expensive though, and military ones are much cheaper.
The military filters are simply active carbon filters with some filtering material. It's better then a mouth cover, but a bit overreacted for the swine flue (49 000 people infected in europe > 100 died.. i'm not that worried, unless they mutate)
The carbon filters start "filtering" when in contact with air, so keep them airtight untill you use them. Basically a world war 2 gasmask would still work fine, as long as it's kept airtight. Same goes for the spare filters.. It's simply a garanteed time that the bundeswehr gets. It's comparable with the EPa.. it will last a life time, but they're rejected after 3 years..
If you want to be fully prepared, and have some money to throw away, buy a new civil one, with a filter for solvents, and one regular for gasses and such (carbonfilter). If you just want it as an "what if" buy some ex bundeswehr (newest available) with some normal issue filters..
And if something happens.. simply get the hell out of there
Sure, someone may one day kill me with my own gun.
But they'll have to beat me to death with it because it's empty.
A computer once beat me at chess, but it was no match for me at kick boxing.
