Surplus gas masks, old, discontinued, out of use gas masks are available from a wide variety of mail order firms that specialize in army surplus equipment. There are army surplus retail outlets and literally hundreds of internet websites. If there is ever a time to let the buyer beware, purchasing a surplus gas mask is it.
To begin with considering the fact that you are buying an old gas mask. How old is it? Was it invented before the leading NBC nuclear, biological and chemical agents were even invented? If so, how effective is it going to be against todays weapons of mass destruction? Possibly not effective at all.
Since the main reason people purchase gas masks of any type is usually because they feel a need to protect themselves against the possibility of a terrorist attack, the most important feature of any gas mask should be its effectiveness against the most commonly anticipated terrorist weapons.
Next, you must research the history of the exact model of gas mask you are thinking about purchasing. It will take some time but it will make a difference. If a gas mask was discontinued by some branch of a military, it is usually because when used, it exhibited some kind of flaw that rendered it unacceptable.
You simply must research its history and discover what that flaw was, because if it defeats the very purpose you are using it for, then perhaps you shouldn’t buy it. However, you may discover that it functions just fine, except under extreme heat or some other situation that still makes it worthwhile for your purposes.
Finally, you must check the filtration system thoroughly before you purchase surplus gas masks. In certain models developed by less advanced countries, the filtration system used chemical agents designed to neutralize the NBC weapons of its day. Some of these filtration systems degenerate over time and the agents used can turn into lethal substances themselves. Surely, a lethal gas mask is an unacceptable contradiction in terms.