Surplus gas masks are accessible from a wide assortment of mail request firms that have practical experience in armed force surplus gear. There are armed force surplus retail outlets and actually many web sites. If there is ever a time to “let the purchaser be careful", buy surplus gas masks.
In any case consider the way that you are buying an "old" gas mask. How old is it? Is it safe to say that it was created before the main NBC – atomic, natural and synthetic – specialists were even developed? Provided that this is true, how viable is it going to be against today's weapons of mass annihilation?
Since the fundamental reason individuals buy gas masks of any sort is typically in light of the fact that they feel a need to ensure themselves against the likelihood of a terrorist assault, the most critical component of any gas mask ought to be its adequacy against the most regularly expected terrorist weapons.
You essentially should investigate its history and find what that defect 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.