Gas Mask

The gas mask is a type of breathing apparatus, designed to filter the various toxic gases that pollute the air of the surface and sections of the metro.

Overview
Gas masks are necessary for those who wander outside of the metro and out on the surface in the ruins of Moscow, as the air is poisonous to any un-mutated organisms. The gas masks likely use charcoal filters, as charcoal is a natural poison absorbent.

In the games, the toxic atmosphere only seems to affect the user's respiration and not the user's skin because Artyom, along with many NPCs, can go out to the surface whilst wearing fingerless gloves and having some parts of their skin exposed; in some of the books, however, professional stalkers take extra care to ensure no skin is exposed to the elements when venturing up top.

After a while on the outside, Artyom will need to change the filters on the gas mask. The maximum filter time Artyom can have for his mask seems to be capped at around 30 minutes; thus he should pass through the surface area quickly since the filter pickup is not common, same with the vendors that sell them.

As Artyom takes impact damage due to melee attacks and bullet impacts, the gas mask will become cracked. The more severe the cracks become, the less time the filters will last. If the mask becomes broken, it must be immediately exchanged for a new one, or Artyom will suffocate. Gas masks can be found littered throughout the surface since many people have traveled to the surface and ultimately died; their gas masks are still usable by Artyom.

There are more than 5 different kinds of gas masks found throughout the game but Artyom seems to be wearing only the full-faced standard mask regardless of suit purchased. Even if his gas mask is severely damaged or completely broken he can only replace it with another full-faced mask. Strangely at the end of the game, Artyom is seen with a Rangers helmet and visor instead of the full-faced mask. If Artyom sprints or jumps the gas mask time will be not affected, however high radiation areas will make the filter deplete faster.

A mixture of different masks from different nationalities, from Czech to Russian to German to others, appear in the games.

Tactics

 * Artyom's breathing can be slowed down by standing near a source of fire.
 * Artyom can survive (ca. 30 Seconds) without a mask. So he can save filters if he just wear the mask every 30 Seconds.
 * Artyom's breathing will be faster while the filter is about to be changed, this is handy in Ranger difficulties since the indicator on Artyom's watch can be hard to read sometimes, especially if player's graphics setting is low. Paying attention to breathing patterns is more useful in Metro 2033 than in Last Light, as in Last Light the indicator on the watch is easier to notice.
 * Artyom's mask becomes increasingly foggy with condensation as his filter runs out. This can be used as an easy means of telling how much time is left on a filter. In most cases, Artyom has about 50 seconds to find a new gas mask or a new filter before dying.
 * In Metro: Last Light, whenever liquid gets on the gas mask (if the character is wearing it at the time), the player character can wait for it to naturally get off, or quickly wipe off the gas mask. It is necessary, but the player doesn't have to do it often, but only if it needs to be done (or if the player feels like their vision is too obscured).

Upgrades
In Metro Exodus, the gas mask, together with the Spartan helmet, count as one piece of equipment that can be upgraded at a workbench. All upgrades are listed below.

Trivia

 * In the game, if the gas mask becomes cracked, it reduces the air filter's duration. In real life, a crack in the mask would not affect the filter at all. Instead, it would simply leak in poisonous air. This is more realistically depicted in Metro Exodus, where the gas mask works normally until it becomes too cracked, whereby the player character is no longer protected from hazardous gas.
 * The gas mask filters the player character uses are very large (bigger than Artyom's hand), but the filters appear very small before being picked up. They are likely 60mm filters.
 * In Metro: Last Light, the type of gas mask Artyom and Anna (along with countless NPCs) use look almost identical to the type used by Russian firefighters, which one would presume cannot offer adequate protection against radiation. However, in reality, the masks doesn't need to block the radiation itself, but rather particles that are themselves irradiated. In fact, anything that filters out dust would do the job, even expired filters.
 * When Artyom changes the filters for the gas mask in the game, he doesn't remove the current filter in the mask, and rather just screws a new one on. However, it's possible that Artyom is either knocking the current filter out of his mask very rapidly or that the mask has a quick-release lever to automatically eject the current filter in use (very few if any gas masks feature this in real life).
 * In the Metro 2033 novel, Artyom is given a tinted full face visor gas mask with two filters on each end, which could either be a GP-10 (as featured in the Metro Universe book Beyond the Horizon) which is/was used by the Russian Civil Defense since 2010. The GP-10 has partly or completely been replaced by the GP-21 (which also features two threads for filters) which, lightly modified is known as the PMK-5 in the Russian Armed Forces. Although none of these masks have tinted visors as standard, it's possible they were modified post-war to help stalkers cope with the light on the surface.
 * Modified masks have also been seen on the first Metro Exodus character art which was published by Gameinformer. It features a PMK-series mask with slight modifications and red glasses.
 * The type of gas mask used by Artyom in the novel is an MF27 industrial gas mask, which is used in a number of nuclear power plants around the world. It's nearly identical to the 3M 6900 Full Face Respirator series except for a small 3M logo on the mouth covering, which the MF27 does not have.
 * It's possible since this gas mask is used by a large number of workers at nuclear power plants around the world, these were all scavenged from a number of nuclear plants in Moscow.
 * Whenever you start a level that requires a gas mask, there will always be a gas mask provided nearby.
 * In both games, Reich soldiers and stalkers have numerous unique gas masks not seen in use by any other faction.
 * In the Metro 2033 alpha, characters wear the Russian PBF Gas Mask and the GP-7, while in the final version, the PBF was omitted and the GP-7 can be found on dead bodies.
 * The Ranger gas mask has no external filters. It's most likely uses an internal porkchop filter, as the Ranger helmet is based on the Czech M10 which itself is based on the American M17.
 * The gas mask on the cover art of Metro 2033 is the USN MARK V.
 * Despite the world model mask having the filter in front, Artyom screws the filter on the left side.
 * The gas mask being pulled off Artyom's face in the Metro Exodus E3 Trailer resembles an American MCU 2/P or could be a PMK-5, although unlikely because versions of the PMK-5 which look similar like the one featured in the E3 Trailer were not seen pre-2014. But, it's possible FSB and other secretive ministries and units already had such PMK-5s.
 * The filters in the Metro games have much shorter lifespans than in real life (a few minutes as opposed to several hours or even days depending on pollution levels). This could be due to the filters being expired; most military-grade gas filters have a shelf-life of a decade or two at most. It's stated that many filters are home-made, which would explain their poor quality.
 * In Metro Exodus, despite having gas masks on their Spartan helmets, rangers will often have a normal gas mask on instead while having the gas mask visor one flipped up.
 * In Metro Exodus, the sound of Artyom's breathing while wearing (and without wearing) the gas mask is notably absent from almost the entire game after the Moscow level. Only returning briefly part way through the Yamantau level and during the "Dead City" level. This seems to be a bug as there is no logical reason for this effect to be missing, and Sam's breathing is heard as normal throughout the entirety of the Sam's Story DLC.

Real gas masks
Gasmaske und FilterППМ-88