A Russian gasmask (possibly the second most common in Russia).
Used for chemical, biological and radioactive agents.
The PPM-88 is a Russian industrial respirator that uses a standard 40mm filter to protect its user from Chemical, Biological, Radioactive and Nuclear (CBRN) threats.
This gas mask is made famous by the game Metro 2033 and Metro: Last Light as it is the mask used by the player throughout the game and is commonly found throughout the game world.
A yellow version can be found.
The PPM-88 and the PPM series is used as most gas masks usually are, for protection against airborne elements. But more specifically, the PPM series was made to protect against radiation in particular; offering this at nearly the same level as the PMK and GP series of gas masks.
The PPM series that is used in industry and by firefighters. They likely are not used by the military, as the PMK-3 seems to be the standard.
Like a lot of Russian masks, very little information about the PPM-88 is available through online channels. Please feel free to add anything you know on this subject.
The PPM-88 is made by the "Briz-Kama Factory", which is part of "Trade House Briz".