[[quoteright:350:[[ComicBook/CaptainAmerica http://static.tvtropes.org/pmwiki/pub/images/Capn_Gas_4187.jpg]]]]
[[caption-width-right:350:If the gas doesn't get us, the KirbyDots will!]]
-> ''Dim, through the misty panes and thick green light,''
-> ''As under a green sea, I saw him drowning.''
-->-- '''Wilfred Owen''', "Dulce et Decorum Est"

Lethal gas is found in many forms and in many environments. It is naturally found in many underground settings (in RealLife as well as in games, particularly near volcanoes) and is abundant in the atmosphere of many planets. Humans have used it as a [[http://en.wikipedia.org/wiki/Chemical_warfare weapon of war,]] a method of execution, and in certain historical mass [[DeathTrap death traps]].

This gas often has a greenish colour, which is more a case of TechnicolorScience than of TruthInTelevision. While chlorine gas ''is'' green, ever since World War 2, nerve gases have been the preferred choice for chemical warfare -- these are colourless and odourless, and can penetrate the body through exposed skin. A common mistake is to depict a gas mask as the full extent of the protective gear needed against nerve gas -- in reality, you would also have to prevent any of the gas coming into contact with the skin.

Another variation is a gas that is not inherently harmful, but fills the space instead of breathable air. In this case, the danger is simple suffocation, and a breathing mask with an oxygen supply is sufficient protection.

In video games, being surrounded by poisonous gas is likely to deplete your OxygenMeter very rapidly.

Sister trope of KnockoutGas, the non-lethal alternative. Not to be confused with {{Fartillery}}.

This trope is always present in a GasChamber. A villain using one has crossed the MoralEventHorizon.


* ''Anime/MazingerZ'': When TheHero Kouji and a [[{{Robeast}} Mechanical Beast]] fought near the crater of a volcano, toxic volcanic fumes pervaded the atmosphere (and unlike other examples of this trope, those fumes had a greyish color). Given that the HomeBase of the heroes was located on Mount Fuji, it happened more often than you would expect. One example happened in episode 19: Kouji is engaged in aerial battle with a Mechanical Beast -Debira X-1-. During the fight they fly over Mount Fuji, and Kouji's visibility gets hindered by the dense curtain of poisonous gas rises from the crater.
* The ''WolfsRain'' episode "The Successors" has a flashback showing how Zali's wolfpack attempted to reach Paradise via a tunnel from their island city. The tunnel filled with toxic gases from the city's factories and many of the wolves died. In the present day the factories have closed, meaning that the tunnel is now safe for Kiba's pack to follow.
* Magellan of ''Manga/OnePiece'', Head Chief of [[TheAlcatraz Impel Down.]] Thanks to his Doku-Doku Fruit, his body is made up of poison, and chlorine gas is his most-used type of deadly gas.
** And waaay down the SortingAlgorithmOfEvil there was Don Krieg, who had poison gas canisters in his repertoire.
** The Punk Hazard arc features [[MadScientist Caesar Clown]], a chemical weapons expert who ate the ''Gasu Gasu no Mi'' which allows him to create, control and turn his body into gas.
*** He also has [[spoiler: a BlobMonster pet named [[FluffyTheTerrible Smiley]], made from the poisonous gas that he unleashed on Punk Hazard four years before the story began. He later fed it a candy that changed it back into its original gas form, only ''MUCH'' deadlier this time around]].
* The Titans in ''Anime/MobileSuitZetaGundam'' used poison gas on space colonies in an attempt to prevent them supporting the AEUG.
** Haman Karn used an earring full of cyanide gas in a failed attempt to assassinate Titans leader Jamitov Hymen at one meeting.
* The later episodes of ''TransformersEnergon'' have [[SicklyGreenGlow glowing green]] "Energon gas".

[[folder:Comic Books]]
* SelfDemonstrating/TheJoker's Joker Venom, which kills while [[DieLaughing making the victim laugh]], is most often seen in gaseous form. This is most notably seen in ''ComicBook/TheDarkKnightReturns'', where he kills an entire live TV studio with weird dolls that exhale Joker Gas.
* In one issue of ''[[ComicBook/GIJoeARealAmericanHeroMarvel G.I. Joe: Special Missions]]'', the Joes have to find a way to stop a Nazi bomber full of experimental nerve gas frozen in a glacier in Greenland from falling into the hands of COBRA.
* ComicBook/CaptainMarVell once had to fight a supervillain who had stolen a container of a deadly nerve gas called Compound 13 and received a dangerous exposure while sealing the leaking container. Although he received an antidote to save his life, the gas also to be carcinogenic and Mar-Vell died from cancer resulting from that exposure.
* ComicBook/{{Diabolik}} is a prolific user of hydrogen cyanide in traps.

[[folder:Fan Works]]
* Pink Cloud from the ''FanFic/FalloutEquestria'' universe is a potent blend of one-third nightmares, one-third NauseaFuel, and one third BodyHorror. It was used by the zebras to exterminate everypony in Canterlot, and it was powerful enough to [[spoiler: [[KillTheGod kill Princess Luna outright and fatally injure Princess Celestia.]]]] In addition to being deadly if inhaled, it [[ImMelting melts skin]] and melds it with anything it touches: floors, walls, benches, [[spoiler: PowerArmor, Pip-Bucks...]] It can penetrate even the tightest-sealed Stable or the most [[Fanfic/FalloutEquestriaPinkEyes advanced enviromental hazard suit.]] And to top it off, it re-animates its victims as ghouls [[LivingMemory who mindlessly repeat their last day on Earth over and over again until their bodies fall apart.]]
* In ''FanFic/TheConversionBureauColdWar'', the Soviet forces are given authorization to use [[http://en.wikipedia.org/wiki/VX_%28nerve_agent%29 VX nerve gas]] on a large platoon of Royal Guards in chapter 7.
* In ''FanFic/WorldwarWarOfEquals'' the Ukrainian government authorizes the use of untested nerve gas on Race forces, killing all who are exposed and in the event that Race forces overrun Jordan, the Syrian government will break out their formerly secret chemical weapon program.
* In the ''WesternAnimation/KimPossible'' fanfic ''[[https://www.fanfiction.net/s/9565191/1/An-Old-Foe-Returns An Old Foe Returns,]]'' Mastermind creates a version that would make simians smarter while numbing the minds of mankind. He nearly succeeded if Ron hadn't tapped into his hidden genius.

* In the first ''Film/{{Batman}}'' movie, this was the Joker's favorite method of killing people. He did it twice, once in the museum where Bruce was supposed to meet Vicki, and once in the big parade scene with big parade-float balloons full of the DeadlyGas. Batman took the balloons away in the Batwing and sent them well away from the city in order to stop him.
** And of course in the comics, the Joker just ''loves'' his Smilex.
*** The [[WesternAnimation/BatmanTheAnimatedSeries Animated Series]] and all other Franchise/{{DCAU}} series where the Joker features also have his signature toxin, though there it isn't so much "Deadly Gas" as it is "[[LaughingMad Insanity-Inducing Gas]]".
** Has the "gas masks protect against nerve gas" mistake twice: first with Vicki Vale in the museum and again when Knox uses a filter mask during the balloon attack.
*** Might be a JustifiedTrope: the Smilex toxin affects the respiratory systems and makes you literally laugh yourself to death, so it might be more like a very potent allergenic agent than an actual neurotoxin.
* In ''Franchise/StarWars: Film/ThePhantomMenace'', the Jedi are trapped by the Trade Federation in a room being filled with nerve gas. Fortunately one of the Jedi's powers are to hold their breath for a very long time. And they were shown later in the movie to have been carrying breathing apparatuses the entire time. [[FridgeLogic Wait, what?]]
* ''Film/JamesBond''
** ''Film/{{Goldfinger}}'' has the titular villain using Delta Nine nerve gas to [[ThrownFromTheZeppelin kill his associates]], and planning to use it in the Fort Knox guards. In a bit of realism, the gas is transparent (and in a bit of "cheap budget", you only see the gas is being used by the sound effect and affected people falling dead, which turns the HeelFaceTurn even easier to figure out).
** ''Film/{{Moonraker}}'' centers around a villain's plan to build himself a space station, then drop satellites filled with enough nerve gas to kill everything on Earth. One scene involves James infiltrating the lab where the nerve gas is being synthesized, taking out a nerve gas canister and looking at it in puzzlement, then sloppily putting it down and hiding in the next room (which conveniently has glass windows and an airlock separating it from where he was) when the scientists come back. The scientists fail to notice the moved canister until one of them knocks it off the table, shattering it-giving Bond a demonstration of the canister's contents and purpose, as the scientists immediately die horribly.
* The RDA in ''Film/{{Avatar}}'' uses tear gas before they cut down the tree's pylons with [[MacrossMissileMassacre missiles]]. Not strictly lethal, but very unpleasant, and very visible.
** Contrariwise, Pandora's atmosphere is toxic to humans.
*** A simple breathing mask is all that humans need to survive the atmosphere for extended duration while leaving the rest of the body completely unprotected. Even getting a good lung full of the atmosphere seems to cause no lasting effects once a human gets back to breathing oxygen. Presumably, then, the Na'vi need oxygen just like we do; the main difference is that there's probably something in their atmosphere (maybe something inert, similar to carbon dioxide but not as greenhousey?) that is toxic to humans, and the filter masks just take it out.
** Supposedly, the atmosphere of Pandora is extremely similar to Earth's save for a few key differences: it's 20% denser, contains 18% carbon dioxide, and 1% hydrogen sulfide. Breathing it in is more or less a lot like suffocation, meaning you'll pass out in 20 seconds or so and die in a couple minutes. Recovering from exposure shouldn't have any sort of effects other than the usual, and I guess prolonged exposure, like more than two minutes, might result in brain or lung damage. So really, all those masks do is scrub out the extra unwanted crap from the atmosphere.
* ''Film/TheRock'' uses a real-life gas, VX. On the other hand, it is not glowing green, and it's not a blister agent. It's a nerve agent. So no, you don't die with [[PoisonIsCorrosive your face melting off and your clothes smoking.]] Instead, your nerves stop working, resulting in [[AndIMustScream paralysis.]] The rest is accurate, though.
* In ''WesternAnimation/{{Nine}}'', gas bombs were the main method used by the machines to [[KillAllHumans kill all the humans]].
* In ''TheAssassinationBureau'', [[spoiler:General von Pinck]] is asphyxiated when his saber pierces one of the hydrogen balloons in the airship.
* ''Film/TheWildGeese''. As they're fighting a war with no Hague Convention, the mercenaries use cyanide gas to silently kill guards in their sleeping quarters.
* In "Pursuit" made from the Michael Crichton novel "Binary" (as John Lange) a psycho milionaire steals US nerve gas and plans to release it over San Diego during a presidential convention (while the president is there). The gas is a binary - two gases each harmless but when mixed cause almost instant (but agonizing death). A film smuggled out of Eastern Europe is shown to the federal agents to demonstrate its effect.
* In ''Film/TeenageMutantNinjaTurtles2014'', [[spoiler:Eric Sacks plans to release a powerful toxin his company created into New York. After wiping out a good percent of the population, he plans to rise up as a hero with an antidote he created with mutagen.]]

[[folder:Live Action TV]]
* In the 2008 ''Series/DoctorWho'' two-part story "The Sontaran Stratagem" and "The Poison Sky", the Sontarans use atmospheric converters fitted to cars in an attempt to replace the Earth's atmosphere with a grey, smog-like vapour that is deadly to humans [[spoiler:but which will nurture billions of Sontaran clone warriors]].
** See also: "The Sound of Drums": Harold Saxon kills his cabinet by Deadly Gas. HilarityEnsues.
** You also have "Gridlock", which features most of the population of New New York all crammed into flying cars in an underground interstate. The exhaust fumes are pretty dangerous for any New Earthlings (or Time Lords) who step out of their vehicles, but the [[GiantEnemyCrab Giant Alien Crabs]] like it just fine.
** Shows up fairly frequently in the Classic Series as well; "[[Recap/DoctorWhoS15E5Underworld Underworld]]" and "[[Recap/DoctorWhoS21E6TheCavesOfAndrozani The Caves of Androzani]]" are two examples. The Fifth Doctor serial "[[Recap/DoctorWhoS21E5PlanetOfFire Planet of Fire]]" inverts the trope by focusing on a gas with particularly healthful properties.
* In ''Series/{{Torchwood}}: Children of Earth'', the 456 live in an opaque, poisonous gas. It doesn't kill anyone though, merely adds to the sense of mystery/horror.
* ''Series/TwentyFour'' had a number of canisters of this as a MacGuffin.
* One ''Series/ThatMitchellAndWebbLook'' sketch had [[{{Calvinball}} Numberwang]] going to Sudden Death, where the winner was the first contestant to inhale enough of the "poisonous number gas" to kill them. We are told that the number 2 is deadly to humans, and it can be seen floating in the tanks.
* In ''Series/TheAdventuresOfSuperman'' episode "[[Recap/TheAdventuresOfSupermanS5E4TombOfZaharan Tomb of Zaharan]]", the gas intended to revive Lois' memory is poisonous, making the titular room a GasChamber.
* In a second season episode of ''{{Fringe}}'', we have a [[ThoseWackyNazis creepy Nazi]] who's genetically tailoring a design toxin that will cause fatal asphyxiation to anyone who isn't blond and blue-eyed. In a [[CrowningMomentofAwesome crowning moment of badassery]], Walter displays his hatred of Nazis by [[TranquilFury coldly re-designing the same toxic gas to only kill the creepy Nazi guy]]. At a ''crowded peace summit'' no less.
* Instead of deadly gas, the Scarrans in ''[[Series/{{Farscape}} The Peacekeeper Wars]]'' use a paralyzing gas. Scorpius notes that they use this on subjects they wish to dissect...while they're still alive.
* Immortal Xavier St. Cloud on ''Series/{{Highlander}}'' liked to kill rich people with poison gas and then steal stuff from them. Or as in the actual episode, rob a jewelry store with that method. He also uses it on a UsefulNotes/WW1 battlefield, killing everyone except immortal Duncan-but can't behead him before immortal Darius shows up and he scurries off.
* Giles, Buffy and Willow almost get gassed on ''Series/BuffyTheVampireSlayer'' in "Out of Sight, Out of Mind", when an invisible girl locks them in the school boiler room and turns on the gas. Angel fortunately arrives in time and shuts it off. They're almost unconscious, but Angel, being a vampire, doesn't have to breathe.
* Shows up in one episode of ''Series/UnnaturalHistory''.
* One of the best DeathTrap scenarios in the AdamWest ''Series/{{Batman}}'' was when the Duo was captured and challenged to avoid drowning in an industrial smokestack for period of time by TheJoker. However, the Joker doublecrosses them by filling the smokestack with a deadly heavier than air gas, noting [[FalseReassurance "Who said anything about water?"]] When Robin protests that you can't float in gas, the Joker responds, "No, but you can ''drown'' in it."
* Occurs in ''Series/{{Helix}}''
** In the pilot, CDC team leader Alan is frightened that KnockOutGas released into the air vents will have this effect on his brother Peter, a research scientist infected with TheVirus who has holed up in {{Air Vent Passageway}}s in the ResearchInc where he works. Alan needn't have worried, the halothane [[SubvertedTrope doesn't faze]] Peter at all.
** In "274" the CDC's veterinary pathologist Doreen has to release this in her lab's observation box to stop the rapid, uncontrollable growth of viral MeatMoss from an infected monkey blood sample.
* At least one ''Series/YoungIndianaJones'' episode depicts a poison gas attack in terrifying detail. Other WorldWarOne-era episodes mention poison gas as well.

* Various kinds of [[http://starwars.wikia.com/wiki/Category:Gases deadly gas]] show up in the Franchise/StarWarsExpandedUniverse.
** ''[[Literature/XWingSeries Wedge's Gamble]]'' had some Rogues being balked by a room flooded with [[http://starwars.wikia.com/wiki/Fex-M3d Fex-M3d]], which would bind to neuroreceptors and make them suffocate. Fortunately, it turned out that one of them [[BizarreAlienBiology didn't breathe]].
** [[http://starwars.wikia.com/wiki/Korfaise Korfaise gas]] was a coolant used on YT-1000 ships like the Millennium Falcon. It was also dangerous to breathe, and in TheThrawnTrilogy Han Solo cut the coolant lines on a YT-1000 to incapacitate the people inside.
** In ''Literature/{{Allegiance}}'', the heroes find a wall with embedded canisters of acidic, corrosive [[http://starwars.wikia.com/wiki/Cryseefa_gas cryseefa]] gas, and have to go through the wall without touching the canisters or setting off the alarms that would make the canisters release.
** The villain of ''Literature/GalaxyOfFear: The Doomsday Ship'' had some such gas at his disposal, but held off on using it because it would kill the heroes too quickly, which wouldn't be as much fun.
* [[AIIsACrapshoot Blaine the train]] from ''Literature/TheWasteLands'' releases this upon [[spoiler:the citizens of Lud]] just before leaving the city. When we find out why, it's because they were ''boring'' to him.
* In ''Literature/ZForZachariah'', nerve gas is used alongside a lot of [[DepopulationBomb depopulation]] [[UsefulNotes/NuclearWeapons bombs]], causing a Class 2, possibly borderline Class 3 ApocalypseHow.
* In Michael Slade's ''Ghoul'', a paranoid bomber in London attempts to kill everyone in a theater with this trope, which he planned to generate by incinerating a whole lot of PFOA-laden Teflon.
* The Martians in ''Literature/TheWarOfTheWorlds'' use the "Black Smoke", a heavy, ink-dark poison gas compound that kills instantly on being breathed. They stay above the dense clouds in their [[TripodTerror tripods]]. The toxin is also designed to be disabled by contact with water, which means that it would pose no long-term danger to them in rainy Britain.
* The Literature/{{Lensman}} universe has Vee-Two, a paralysant which is lethal if not reversed within a short space of time. The Triplanetary Patrol carries the antidote at all times because space pirates are always using it, a fact used to effect by Conway Costigan on two occasions. Although it's clearly a neuroactive gas, it seems to act by inhalation only as a mask is protective.
* ''Literature/{{Animorphs}}'': all Gleet Bio-Filters at Yeerk Pool enterances are equipped with poison gas in case of entry attempts by unauthorized life forms. The main characters barely make it out alive when they trigger one.
* In Creator/MichaelCrichton's ''Literature/{{Binary}}'', The BigBad plans to use a deadly binary nerve gas to wipe out an entire city.
* In the Literature/SherlockHolmes story [[spoiler:"The Adventure of the Devil's Foot"]], Deadly Gas turns out to be the murder weapon.
* The MacGuffin of ''The Chinatown Death Cloud Peril'' (a [[TwoFistedTales pulp-homage novel]] by Paul Malmont) is a US Army experimental poison gas left over from UsefulNotes/WorldWarI. Its effects are not pretty.
* In ''Literature/DeadBeat'', the White Council has evacuated their wounded to a hospital in the Congo. The vampires [[spoiler:cannot attack directly because it's broad daylight (and because the Council has thrown up some very strong wards), so they have their thralls bomb everything within a six-block radius of the hospital with [[http://en.wikipedia.org/wiki/Sarin sarin gas]]. Tens of thousands of completely uninvolved mortals were wiped out, along with dozens of Council Wardens]].
* In ''Literature/TheVorkosiganSaga'', the chemical weapon Fetaine is non-lethal in effect, but it is so feared by Barrayarans that Miles grimly reflects that it could never have actually been used. It's a violent mutagen, described by a doctor as "unravelling all the DNA in your balls", ensuring that if you do have any children, they will be mutants. Naturally, Miles' commanding officer of the time is absolutely determined to preserve their stockpile of the vile stuff after a stupid accident endangers it, and doesn't seem to care that he is ordering his men to march straight into a fate they all regard as far worse than death (He does intend for them to wear protective gear - he's not ''completely'' insane - but he ignores his technical expert's warning that standard chemical warfare gear is probably inadequate for Fetaine). More frequently mentioned in-series is Soltoxin; Miles' parents survive a Soltoxin gas attack, while his mother is pregnant with him, which results in him being born with a vast array of crippling medical problems which plague him for the rest of his life.

[[folder:Tabletop Games]]
* ''TabletopGame/DungeonsAndDragons'' includes numerous poison gases, ranging from the merely tear gas-like Stinking Cloud to the extremely lethal Cloudkill.
** Apart from spells that create clouds of poisonous gas, like those mentioned above, there are also mundane poison gases, such as Burnt Othur Fumes and Insanity Mist.
** The 1st Edition adventure ''Hidden Shrine of Tamoachan'' is set in an abandoned temple which is filled with a mild toxic gas. It causes gradual hp loss every few minutes until the heroes reach a more-ventilated level of the complex.
* ''TabletopGame/{{GURPS}}: Ultra-Tech'' and ''High-Tech'' both have generic poison gases. Ultra-Tech also has a clever variant on it, a cloud of microbots that inject the poison into people.
* ''TabletopGame/{{Shadowrun}}'' has two types of nerve gas: Green Ring 3 (from RealLife) and Seven-7, a fictional gas that can penetrate normal chemsuit protection.
* Classic ''TabletopGame/{{Traveller}}''. Several adventures in Supplement 6 ''76 Patrons'' involve PC attempts to acquire nerve gas produced by the MegaCorp Schunamann und Sohn, AG.
* The [[BadassNormal Imperial Guard]] in ''TabletopGame/{{Warhammer 40000}}'' have access to a tank variant known as the Bane Wolf - it's only short ranged, but fires a cloud of toxic chemicals that kills off almost all infantry in one blast.

[[folder:Video Games]]
* The gas you can throw in ''VideoGame/{{MAG}}'' is substantially less dangerous than the other examples on this page, but it's effective as an area denial weapon.
* This is somewhat common in ''VideoGame/WorldOfWarcraft''. You would be surprised how many people [[TooDumbToLive don't understand how to not stand in it]].
** Weaponized by the Forsaken in the form of [[FantasticNuke Blight]], a virulent plague hurled in barrels by their catapults. To make matters worse, over time large concentrations can settle into pools that may spawn sentient slime.
* DiabloIII: Do NOT stand in Ghom's gas attack. Because other than the fact that it deals significant amounts of damage per second? "Ew".
* In ''VideoGame/FinalFantasyCrystalChronicles'', the plot is about removing miasma (deadly purple gas) from the world.
* In ''[[VideoGame/BanjoKazooie Banjo-Tooie]]'', this can be found in many places, including the part of Glitter Gulch Mine where you rescue Canary Mary, packed into barrels in Grunty Industries (many of these barrels are [[EverythingTryingToKillYou trying to kill you]], of course), and released by Gruntilda as part of the FinalBoss battle.
-->'''Gruntilda''': Mmmm, cyanide and mustard gas flavor. My favorite!
* ''VideoGame/SuperMario64'' has the Hazy Maze Cave, which has the aptly-named Hazy Maze complete with poison yellow gas. Unless Mario is wearing the Metal Cap, prolonged stays in the Hazy Maze prove to be fatal.
** In the DS remake, the gas is purple, and it's Metal Wario that can survive in it. If any character gets a hidden Mega Mushroom, they can stand in it since their heads are physically above the gas... until the mushroom wears off. Also, any character in the gas actually ''coughs visibly'' if you don't move them while losing health.
** Don't forget [[TheManyDeathsOfYou the unique death animation]] for this. Your character actually chokes and falls over, dead.
* Greenish poison gas -- and it's always ''greenish'' poison gas -- is quite common in ''VideoGame/DeusEx''. It's available in movable/puncturable barrels, for a little variety from the [[ExplodingBarrels usual kind]], as well as gas grenades. At one point you, can play with some in the ventilation system and [[VideoGameCrueltyPotential gas a whole facility of people]].
** The green poison gas returns in ''VideoGame/DeusExHumanRevolution'', in the form of occasional environmental hazards and gas grenades. Jensen can get an augmentation that negates the effects of gas, allowing him to use grenades like smoke bombs when mobbed. Also, toxic gas is specifically ''not'' deadly (for the enemies) in both games, and a gas grenade is easily the best nonlethal option for groups of enemies (important in Human Revolution if you're chasing after the Pacifist achievement).
* In ''VideoGame/KingOfFighters '95'', poisonous gas makes an appaearance... but only in cut scenes, as Rugal uses sleeping gas to kidnap the KoF champions and bring them to his presence.
* ''VideoGame/TheLegendOfZeldaTwilightPrincess'' has one area with a deadly ''purple'' gas/mist that can be temporarily locally dispelled by waving a lantern about.
** Although not itself deadly, there is a purple poison gas in ''[[VideoGame/TheLegendOfZeldaTheWindWaker The Wind Waker]]'' that temporarily disables your ability to attack or use items, and there are usually enemies in the gas. Later in the same dungeon there are purple [[GoddamnedBats flying skulls with the same ability]].
* ''[[VideoGame/Sonic3AndKnuckles Sonic & Knuckles]]'' features Toxomister badniks in the Lava Reef Zone that spew clouds of deadly gas. If you get caught in one, it slows your speed to a crawl, drains your rings until you die, and is also one of the few things that [[SuperMode Super/Hyper Sonic]] ''isn't'' immune to. The only way to dispel the cloud is to [[NoOntologicalInertia destroy the Toxomister that made it.]]
* In ''VideoGame/{{Portal}}'', in the final level, after you [[NiceJobBreakingItHero destroy [=GLaDOS=]'s morality core]], she starts releasing a deadly neurotoxin into the room; you have only six minutes to finish the job before the gas kills you. How did she get the ''deadly'' neurotoxin? It appears that the researchers gave it to her (presumably related to UsefulNotes/SchrodingersCat). And then [[TooDumbToLive she killed them with it]].
** ''VideoGame/{{Portal 2}}'' brings the deadly neurotoxin back and makes it a greater part of the plot. Part of Chapter 4 involves shutting down the production facility so [=GLaDOS=] will be deprived of it as a weapon. It then makes a reappearance, albeit briefly, in the FinalBoss fight.
*** It also makes a brief appearance after you break out of the testing chambers. [=GLaDOS=] will attempt to get you back into the chambers by opening up a chamber with a heart on the wall. If you are stupid enough to go into the chamber, she will flood it with neurotoxin, killing you instantly. This leads to some FridgeLogic: Why did it take the neurotoxin 6 minutes to kill you in the first game, but only 3 seconds in the second game?
** The second game, and all the side media like the Ratman comic, firmly establish [[InsistentTerminology Deadly Neurotoxin]] as [=GLaDOS=]' WeaponOfChoice.
*** And in the Perpetual Testing Initiative DLC, we have mentions of an alternate Earth's governing body, a sentient cloud which can come in under doors and leech the skin off people.
* The ''Franchise/MetalGear'' series often will fill rooms with poison gas, which necessitates either very brief stays or a gas mask.
* In ''VideoGame/CommandandConquer: Tiberian Sun'', the Brotherhood of Nod weaponizes [[GreenRocks Tiberium]] in the form of a [[ExactlyWhatItSaysOnTheTin Chemical Missile]], which detonates over the target area and saturates it with noxious clouds of highly-corrosive gas. Its effects on infantry are... [[BodyHorror unsettling, to say the least]].
** Before that, the ''Covert Ops'' addon for the first game had Chemical Troopers, a variation on the normal Flamethrower infantry who sprayed Tiberium gas, instantly fatal to any non-Chemical Trooper infantry.
* The Intruder Excluder level in ''VideoGame/{{Battletoads}}'' has traps that shoot small puffs of gas, instantly fatal.
* The Borely Haunted Mansion in ''VideoGame/SilentHill3''. In one section, Heather must avoid a strange red gas that follows her from room to room. No matter what difficulty you're playing on, if the gas touches you it's instant death.
* The ''VideoGame/JaggedAlliance'' PC games let both your mercenaries and the enemy chuck mustard gas grenades around, unleashing clouds of ridiculously lethal yellow gas. Not instantly lethal, but it may as well have been since characters would collapse after one or two rounds of exposure and invariably die from poisoning in the middle of the gas cloud. [[note]]Mustard gas is strongly mutagenic and carcinogenic, and causes severe chemical burns and ''bleeding in the repiratory tract'' - there's a reason it kills so quickly. The vesicating effect is what is most lethal. Victims might well drown in fluid released from the blistering in the lungs.[[/note]]
* ''VideoGame/IronStorm'', an AlternateHistory FPS that extends WWI-era fighting and technology many years after the real world's WWI had ended, features mustard gas grenades.
* ''[[VideoGame/{{Doom}} Doom 3]]'' includes a level centered around escaping a location which is slowly filling with poison gas. Said gas obeys all traffic laws in that it is properly green and slowly drains your health (complete with choking sounds) ''up until the second'' you finally hit the "Vent Gas" switch, at which point it is instantly drained from the entire location and ceases being harmful. Apparently the Mars base has some powerful gas vents.
* ''VideoGame/HarvestMoon Magical Melody'', in the mines, rocks sometimes give off certain gasses with different effects, some bad, a few good. This also happens in ''Tree Of Tranquility'' and ''Animal Parade.''
* In ''VideoGame/ResidentEvilOutbreak File #2'', you must search the Raccoon City Police Station to find all the necessary items to escape the zombie siege. As a "riot control" measure, the crazy police chief has wired up ''his own police station with random nerve gas dispensers''.
* ''VideoGame/ParasiteEve2'' used this by trapping Aya in a sterilization room and releasing the gaseous chemicals that slowly drain her HP unless she jumps in the garbage chute to escape. Also used again later on when she and Eve are trying to escape from Golems that fill the room with gas. While Aya isn't affected, despite her coughing, it hurts Eve and saps her HP; having her die results in a [[WeCannotGoOnWithoutYou Game Over]].
* ''VideoGame/RiseOfTheTriad'' had several rooms fill up with deadly gas shortly after you walk in. There was always at least one gas mask somewhere in the room and picking it up would protect you from dying. Since the enemies were never clever enough to do the same you could then just wait for them to die. The gas drained away by itself after a minute.
* In ''VideoGame/{{Hexen}}'' the Flechette item works differently depending on your character class. If playing as a Cleric dropping a Flechette creates a cloud of DeadlyGas that will severely damage anything trying to walk through it (including your character).
** Also, certain levels in ''VideoGame/{{Hexen}}'' contained special mushrooms that emitted DeadlyGas. The mushrooms were covered in green pustules, made weird squeaking noises, and released the gas when damaged.
* Fox gets trapped into a room full of poison gas in ''VideoGame/StarFoxAdventures'', where he has to solve a BlockPuzzle in order to escape.
* In ''VideoGame/FinalFantasyVII'', Tifa is nearly executed this way.
* In an old UsefulNotes/AppleII text adventure game with graphical aid, ''MaskOfTheSun'', at one point you are locked in a room filled with gas (which the game presents by showing an entirely green screen). To get out without dying (and you have a limited time), you have to figure out the exit is on the southwest, a direction atypical to text adventures at the time.
* In ''VideoGame/BreathOfFireDragonQuarter'', after Ryu, Nina, and Lin return to the EndSector Borough to find three Rangers have ambushed them with a tank of poison gas.
* All over the place in ''VideoGame/KnightsOfTheOldRepublic''. Sort of subverted in that you can break into computers to use the gas systems against your enemies.
** Even weirder is the ''VideoGame/StarWarsTheOldRepublic'''s healing gas. Yep, that's right: medical supplies that can be thrown to produce a healing vapor that seeps into your character's skin and heals them. Of course, given the various ridiculous ways that players can heal, this is practically a given.
* The ''VideoGame/MetroidPrime'' games included Puffers, which upon exploding, released green gas that was harmful to Samus.
** One room in the Phazon Mines had it until you found the panel to scan to turn on the fans. [[spoiler:You need the Power Bombs before you can find it.]]
** Also, in ''Metroid Prime 2: Echoes", Dark Aether's entire atmosphere, as well as the gas that Emperor Ing's second form releases into the room.
* In ''VideoGame/DeadSpace'', one mission has Isaac fighting his way through the ship's hydroponics lab, killing necromorphs that were poisoning the atmosphere. He can survive due to his air-tight engineering suit, designed to operate in vacuum.
* ''VideoGame/{{Crystalis}}'' had an entire swamp filled with toxic gas. If you didn't have a gas mask, you would probably die before you reached the town hidden inside because of how rapidly it drained your HealthPoints.
* In ''VideoGame/TheSuffering'', one of the bosses, [[spoiler:a former warden responsible for gas executions and killed himself in the gas chamber]], is anthropomorphic poisonous gas, specifically the kind used in prison gas chambers. The green color is justified almost immediately; while the actual gas used for executions is invisible, he likes to make his gas visible [[KickTheDog to let people he kills know they are about to die]].
* The Gas Grenade from ''VideoGame/SyphonFilter''. In the first game, it was the [[PuzzleBoss only way to beat the]] FinalBoss, who was wearing full-body armor that made him NighInvulnerable, but still required him to breathe.
* In ''VideoGame/TheWhiteChamber'', it's possible to die from toxic gasses that result from not getting rid of [[spoiler: the dead body inside the fridge.]]
* ''VideoGame/ThePowderToy'' has caustic gas, which dissolves everything it touches and is sometimes used in bombs.
* IG-88 in ''VideoGame/EmpireAtWar: Forces of Corruption'' has, as his land special abilities, an ability that irradiates an enemy unit, and one that release poison gas over an area. The gas is toxic to enemy and allied units.
* In the N64 game for ''VideoGame/TheWorldIsNotEnough'', there is one point in the game where security camera's detect you and lock you in a room with poison gas coming in through vents, which you can only escape by using the grappling hook in your wristwatch. It is, however, possible to escape this by shooting the camera's, which promptly explode, before they detect you and gas starts pumping into the room.
* ''Franchise/ResidentEvil'' games are ridiculous with poison gases - ineffectiveness. They are often used if you fail to solve a puzzle correctly. In many cases, gases pumped into a room won't do ''anything'' [[CriticalExistenceFailure until after some arbitrary time limit passes and kills you instantly]]. In one case, gas is pumped into a room where it sits as a yellow cloud ''at knee-height and never moves'' until you vent it. As [[http://lparchive.org/LetsPlay/RECV this Let's Play says]]: "Diffusion? Who needs it?"
* In ''VideoGame/StarWarsRepublicCommando'', the second run through the detention block level ends with you defeating the ambush with the anti-jailbreak system, which releases DeadlyGas in a rather fruity pink colour. Fortunately your squad is immune since the designers remembered ''why'' Storm/Clonetroopers are FacelessMooks and have your armour provide HAZMAT protection. The enemies...aren't so lucky.
-->'''Scorch:''' That's the last one! I guess we know how long Trandoshans can hold their breath.
* ''VideoGame/LittleBigPlanet'': [[ExactlyWhatItSaysOnTheTin Horrible Gas]]. If a Sackperson touches it (even with their arms or feet, not just their head), they ''dissolve''. Horrible Gas actually comes in six colors, but green is the most common. The others are used mostly to make the player think it's something else, like gray gas for fog, or purple gas for some kind of monster-related thing, as seen in the "Monsters" level pack. Unless it's deliberately attached to something else (done by gluing a material to a Piston or another material before lethalizing it with the Horrible Gas Tool, as shown by the ghosts of the third level of The Gardens), it stays in place and cannot be moved. Anything that isn't a Sackperson can move through the gas, however. A lot of level creators have this as their hazard of choice, though [[XRaySparks electrified materials]] and the plasma balls of the ''VideoGame/MetalGearSolid'' pack are just as lethal. Fire, on the other hand, takes two hits to kill a Sackperson.
* In ''VideoGame/RatchetAndClank'', the planet Orxon is covered in green, noxious gas from the pollution, making it impossible to explore without the O2 Mask that you obtain from Pokitaru. When it reappears in ''VideoGame/RatchetDeadlocked'', the atmosphere is apparently capable of sustaining life again.
* Green gas barriers are a standard obstacle in the ''VideoGame/{{Overlord}}'' series, usually put in place to keep you from advancing too far until you've gotten your Green Minions back.
* In ''VideoGame/PerfectDark'', Joanna Dark infiltrates Area 51 to rescue an alien survivor. When she reaches the room where he is located, the scientists flood the room with poison gas. Of course, [[TooDumbToLive the scientists kind of forgot they were still in the room as well.]]
** In ''Perfect Dark Zero'''s Laboratory Rescue mission, the laboratory gets flooded with green gas that slowly drains your health and prevents it from regenerating until you activate the ventilation.
* ''VideoGame/{{Prototype}}'' features Bloodtox, a red gas that causes necrosis in infected tissue. It's apparently completely harmless to humans, but it drains Alex Mercer's health (but its stated he's ''growing resistant'' to it).
* ''VideoGame/StubbsTheZombie''. It doesn't matter if the main character sets off the poison gas, because he is a zombie. It's a problem if you are remote controlling a human and still have some more victims to kill. Oh well.
* The main area of the Twin Labyrinths in ''VideoGame/LaMulana'' has a DeadlyGas trap represented by clouds drifting along the screen and a 30-second timer. To eliminate the gas, you must weight two pedestals before the timer runs out. Curiously, in the original version, if you fail, you get booted back to the previous area instead of dying; in the remake, you lose health very rapidly instead.
* ''VideoGame/TimeSplitters: Future Perfect'' features a gas-chamber deathtrap on Khallos' train. Lampshaded by Harry Tipper:
-->"Oh no! Green gas! That's the worst kind!"
* Green gas makes players faint in ''[[VideoGame/BackyardSports Backyard Football]]''.
* Samara's recruitment mission in ''VideoGame/MassEffect2'' involves storming a mercenary base full of tanks of a tainted gaseous drug which an unscrupulous merchant sold to the mercs. The deal is, inhaling the gas gives the user a sizable boost to [[MindOverMatter biotic]] abilities, but causes death after prolonged use, a fact that the merchant happened to not mention. Gameplay-wise, the canisters can be detonated during the level, and standing in the gas temporarily improves the squad's biotic ability, but standing in it for too long will lead to a GameOver.
* ''VideoGame/{{Worms}}'' features the worlds least-deadly deadly gas, as it doesn't actually kill affected worms, just slowly reducing their life points to 1.
* ''VideoGame/CallOfDutyBlackOps'' has Nova-6, a chemical weapon originally developed by the Nazis then refined by the Soviets. A cloudy, green gas that causes near-instant necrosis all over a victim's body, the latter version capable of killing in seconds with minimal exposure, [[spoiler: and planned by [[BigBad Dragovich]] to be released all over the United States.]] It's available as a tactical grenade in multiplayer, though it's [[{{Nerf}} nerfed]] to an incapacitant rather than instant death.
** ''VideoGame/ModernWarfare 3'' also has deadly green gas used on the battlefield. [[spoiler: Makarov's men used dirty bombs in most major European cities, crippling the nations and paving the way for Russian invasion.]]
* ''VideoGame/CallOfDutyAdvancedWarfare'' has Manticore, a toxin developed by the Atlas Corporation. Basically, it's a nerve agent that only affects certain types of DNA: anyone isn't registered on Atlas dies almost immediately.
* The ''Franchise/{{Pokemon}}'' Koffing and Weezing have bodies that contain very poisonous gas and there are several Poison-type moves related to gas, like Smog, though some (despite being dubiously named) are [[SubvertedTrope perfectly harmless]]. Not to mention there's also a move specifically named "Poison Gas." [[DepartmentOfRedundancyDepartment It poisons things]].
* ''VideoGame/NoOneLivesForever'' has cyanide gas, which gives you hallucinations while draining your HitPoints. Oh, and it looks green. The cyanide bullets have the same effect.
* In one level of ''VideoGame/StarTrekEliteForce II'', your team is trapped in a room that is being filled with poison gas (how the aliens knew it would affect any humanoid is not explained). You, as [[PlayerCharacter Alexander Munro]], have to use your [[EmergencyWeapon Type 2 phaser]] (which has a continuous beam) to fuse the gas vents. After that, the gas that has already been pumped into the room is, apparently, rendered harmless.
* In ''VideoGame/DragonAgeII'', some thieves hoping to incite anti-Qunari feeling steal what they ''think'' is the formula for Qunari blackpowder. It's actually a decoy - the formula for a poison gas called sar-qamek. Not only does it kill, but it first drives the victims mad and turns them against each other.
* ''VideoGame/RuneScape'': In "The Path of Glouphrie", brightly-colored poison gas is used as part of a DeathTrap.
* Nerve gas is a tactical aid option in multiplayer matches of ''WorldInConflict.'' True to real life, it's horribly lethal to infantry while leaving structures and vehicles unharmed. [[VideogameCrueltyPotential Useful for digging infantry out of buildings you want to use for yourself.]]
* ''VideoGame/GoldenEye1997'' has a room full of gas tanks in the Facility level, but if the tanks are destroyed the gas will slowly kill you and you will fail the level.
* In ''VideoGame/DragonQuestIV'', there's a yellowish gas coming out of Mamon mine [[spoiler:because that's where Estark is buried]]. While it makes the locals sick and eventually kills them, [[GameplayAndStorySegregation it has no effects on player characters]].
* In ''VideoGame/{{Ys}} II'', one area is filled with toxic gas, which the Roda Tree Leaf protects against.
* The original ''Videogame/AloneInTheDark1992'' has a smoking parlor where the smoke will drain Carnby's health unless you extinguish the ashtray with a water jug.
* In ''VideoGame/FalloutNewVegas: Dead Money'', the Sierra Madre is contaminated by the Cloud, a highly toxic red smog that also [[PoisonIsCorrosive corrodes metal]]. This may have inspired the Pink Cloud in ''FalloutEquestria''. On Hardcore mode, it slowly saps the Courier's HP outdoors, with more concentrated pockets causing faster health loss.
* Pops up a few times in horror adventure game ''VideoGame/TheCatLady'' in the form of the deadly [[http://en.wikipedia.org/wiki/Hydrogen_sulfide hydrogen sulfide]]. Mitzi[[spoiler:'s boyfriend uses it to kill himself]], Susan uses it [[spoiler: to kill the second Parasite]], and the Eye of Adam uses it to [[spoiler: attempt to kill Susan and Mitzi, claiming his own father's life in the process]].
* In ''VideoGame/KZManager'' you must buy [[ThoseWackyNazis Zyklon B]] to [[FinalSolution gas]] [[VillainProtagonist your]] inmates.
* Reisen in the ''{{Touhou}}'' fighting games has a spellcard called Poison Smokescreen "Gas-Woven Orb". She smashes a vial on the ground, releasing a drug that turns into a LifeMeter-sapping poison gas that lingers close to the ground like a cloud of green death. It alone can't KO an opponent, but its damage can add up.
* ''VideoGame/BravelyDefault'' has the Toxic Mist, a weapon capable of killing one hundred thousand soldiers, friend and foe alike, and rendering the land uninhabitable for years. Dr. Qada, its inventor, is a firm believer of WeHaveReserves, as he doesn't feel any guilt over the massive friendly fire the weapon causes.
* In EverQuest the gods created a poison gas (the "Greenmist") to wipe out the [[AbusivePrecursors Shissar]]
* ''VideoGame/StarFoxAdventures'' has gas in a few places that make Fox fall over in his OxygenMeter runs out, and you have to restart the sequence:
** There's a sort of switchback that you have to travel through each time you want to go between Thorntail Hollow and Moon Mountain Pass, hopping on pillars that rise and sink to get across to the updrafts that push you out of it.
** In Cape Claw, there's a room with four blocks around a central support. When you step on a certain point, the door shuts and the blocks move away to the corners of a square, and you have to drag and push all of them back to stop the poison. (Why would you go there in the first place? Well, there's a good reason...)
** The Power Room in Cloudrunner Fortress is filled with gas until you place the three Power Gems on their pedestals. At least you can leave if you need to.
* ''[[VideoGame/SonicChronicles Sonic Chronicles: The Dark Brotherhood]]'' has gas that simply acts like a wall in terms of gameplay... except to characters like Big.
* The ''{{Dark Souls}}'' games had several of these as spells, {{Color Coded For Your Convenience}} depending on their lethality; Poison Mist is a sickly green, the more lethal Toxic Mist a virulent orange, and the Dark Mist a grey colour. There were also spells that generated clouds of yellow gas that did no damage but grievously damaged the equipment of anyone passing through.
* In ''VideoGame/{{Bioshock}}'', Ryan kills off the vegetation in Arcadia with a yellow-brown herbicide, then uses a similar-colored gas to kill Julie Langford.

[[folder:Web Comics]]
* {{MAG ISA}} -- [[http://mag-isa.thecomicseries.com/comics/pl/119508 Fr. Jose gets poison gas sprayed at him by a demon in the confessional]].
* In ''Webcomic/DarthsAndDroids'', following the plot of the StarWars prequel trilogy, the room where the characters were supposed to hold some negotiation is filled with toxic gas.[[note]]Revealed in a [[http://darthsanddroids.net/episodes/0183.html flashback]] to be knockout gas.[[/note]] The players continue talking in character, ''[[TalkingIsAFreeaction while holding their breath]]''. [[LampshadeHanging Lampshaded]] of course, by the DM.
* The Land of Tombs and Xenon in ''WebComic/{{Homestuck}}'' has this kind of atmosphere, a (likely deliberate) bending of the laws of chemistry as xenon in real life is non-toxic but asphyxiant (and tends to pool at the bottom of the lungs as it's difficult for the body to expel). However, the characters refer to it as poison gas and use gas masks to protect against it (rather than oxygen tanks, which is what you'd actually need).

[[folder:Web Original]]
* [[MadScientist Carina Appelbaum]] from v2 of ''WebAnimation/OpenBlue'' included vials of DeadlyGas amongst her many other mysterious chemical weapons, which explained why the crew and marines on her ship all wore [[GasMaskMooks gas masks]].
* As his name implies, the villainous Belcher of the ''WebAnimation/GlobalGuardiansPBEMUniverse'' can let loose with weaponized burps. Mostly he uses noxious gases, but has been known to let loose with a [[PlayingWithFire gout of fire]] occasionally.
* In one ''WebAnimation/HomestarRunner'' cartoon, Strong Sad imagines all the rest of the cast meeting horrible fates. He drops an O from the Poopsmith's name and has him pop Pom Pom, leading to:
--> Pom Pom was filled with a deadly gas, which killed the Popsmith very fast.
* In ''WebAnimation/TheSalvationWar'', during the battle for the banks of the Phlegethon river in Hell, the Russians drop sarin gas shells on their own tank positions when they are overrun by Beelzebub's fire-breathing harpies; most of the crews were safe inside their sealed positive-pressure tank hulls, but the harpies were completely unprotected and were killed in their thousands.
* ''Wiki/SCPFoundation'' has an odd example in the case of SCP-681, a malevolent form of helium (in real life a non-toxic asphyxiant) that intentionally coats the inside of the lungs of living beings in the most efficient possible manner, causing them to suffocate. Luckily, it can be trapped in balloons.

[[folder: Western Animation]]
* One of the many types of gases used by the vile borg, Noxious in ''WesternAnimation/SkysurferStrikeForce''.
* In ''WesternAnimation/TeenageMutantNinjaTurtles2012'', the yellow gas on the Kraang's planet that they recreate in the TCRI building is toxic to Earth beings.

[[folder:Real Life]]
* As mentioned before, chlorine is distinctly green, and rather nasty to breathe. Chlorine, however, will generally not try to eat its way out of its container, unlike its sibling one row up. Fluorine is a yellowish-amber color, but if you ever see enough of it to see the color, you'd best hope it's [[http://theodoregray.com/periodicTable/Elements/009/index.s7.html#sample5 properly secured]] or you're already dead. The heavier halogens are easier to handle since they don't evaporate at room temperature, but if you do heat them up the vapours are almost as nasty.
** Elemental fluorine is one of the most difficult chemicals in the world to handle properly because it reacts quickly and violently to almost everything except some metals and chemicals. It will happily consume even the most invisible quantities of water and eat straight through glass. It is ''the'' most electronegative chemical known, meaning it bonds to almost any other element and absolutely will not let go without some serious chemical prodding. (It also bonded with a good number of 19th century chemists trying to isolate it, who are now remembered as the "Fluorine Martyrs".) Fluorine's sheer reactivity, in fact, makes it ideal for creating nonreactive substances like Teflon and non-polluting refrigerants, as well as a number of oddball uses in medical chemistry. That roll of Teflon sealing tape in your toolbox? Nearly 80% fluorine by weight... and, chemically, possibly the single safest thing in your house.
** Even fluorine pales in comparison to [[http://pipeline.corante.com/archives/2008/02/26/sand_wont_save_you_this_time.php chlorine trifluoride]], which will happily set things like water, bricks, sand, and ''asbestos'' on fire. Said reactions will inevitably produce dangerous by-products like hydrofluoric acid, which painlessly passes through skin leaving a mild burn...and painfully dissolves your bones, spreading along your skeleton. And then goes into your blood, giving you a heart attack due to hypocalcemia.\\
[[=CF3=]]'s attempted use as a rocket propellant oxidiser was documented in the book [[http://library.sciencemadness.org/library/books/ignition.pdf ''Ignition'']] by John Clark, a history of US propellant research with some very funny anecdotes about the people involved; it seemed that it was fine held at rest in most metal containers, but it started eating through everything as soon as you tried to move it anywhere. Clark mentioned a story about a substantial spill of the stuff that ate through a three-foot-thick concrete floor and created a cloud of nasty reaction products in the process.\\
And, if this isn't horrible enough for you, during WWII UsefulNotes/NaziGermany ''weaponized it'': [[http://en.wikipedia.org/wiki/Chlorine_trifluoride#Military_applications N-stoff]] was, in effect, a chemical weapon that set its victims on fire. Thankfully for the battlefields of Europe, only 50 tonnes were ever produced and these were captured unused by the RKKA in 1945.
* A good number of toxic gases were used as weapons in UsefulNotes/WorldWarOne along with chlorine -- phosgene, lewisite, mustard gas, among others. UsefulNotes/AdolfHitler [[EvenEvilHasStandards experienced this personally and refused to allow their use in]] UsefulNotes/WorldWarTwo, although the Germans were world leaders in developing chemical arms, including sarin and tabun.
* The Russian authorities in the 2002 Moscow theatre siege used (tragically ineptly) a KnockoutGas called Kolokol-1, believed to be a highly potent derivative of fentanyl, an opioid so much more powerful than morphine already that it can only be given to cancer patients who have become morphine-tolerant.
** Fentanyl (and a ''[[UpToEleven five to ten times more powerful variant]]'' called Sufentanil) are extremely commonly used IV analgesics for surgical anesthesia. Sure, you wouldn't use it for extended periods, but that's mainly because it's powerful enough to easily cause respiratory suppression. (As the Moscow police learned, we might note.) Terminal, drug addicted cancer patients are hardly its core demographic.
* The 1998 Tailwind scandal, based around a (possibly but not definitely discredited) CNN story of Vietnam-era war crimes supposedly committed by US troops in Laos, revolved around a dispute over whether chemical weapons were used, including nerve gas and/or tear gas. At least one account of the story included a chemical code-named "Glink", which was supposed to paralyze everyone on the ground where it was spread; the idea was that medics were supposed to show up on rescue helicopters and give the antidote only to friendlies. (Disputes over the accuracy of the report led to a round of firings at CNN, but the original producers of the report stand by their content.)
* According to experts, hydrogen sulphide (the rotten eggs smelling gas) is odourless in lethal concentrations. A high enough concentration of hydrogen sulphide numbs your nose completely (and for several days, by the way). So if you stop smelling it then you are either perfectly safe, because it has gone, [[ParanoiaFuel or going to die, because it hasn't.]]
* Oh, and don't mix ammonia and bleach together. You'd ''think'' it would make your cleaning job go faster by combining two cleaners. In reality, it's more likely to create a nasty gas called chloramine, which can knock you unconscious and/or kill you. (This is especially true if your mixture is very concentrated, and/or the room poorly ventilated.)
** And, in fact, people have died for this exact reason. In Philadelphia in early January 1995, a 61-year-old man mixed bleach, ammonia, and a commercial drain cleaner to try to unclog an upstairs toilet. The result was chlorine and phosgene gas, which quickly knocked him unconscious followed by death due to suffocation. This may have been the inspiration for the 1000WaysToDie story "Trailer Trashed".
** Bleach is commonly used as a cheap alternative to toilet cleaner, and urine is high in ammonia. This has lead to many accidental deaths and injuries, including burnt genitals.
** Similarly, several people have died by trying to clean pools with ammonia. Even coating the sides of empty pool with ammonia can be fatal.
** This is used in a episode of WesternAnimation/KingOfTheHill when Peggy was writing some general housekeeping tips in a newspaper article and wrote that bleach and ammonia make a great stain remover. Hank had to gather all the newspapers before it killed everyone (she had been previously been fed real tips for articles so everyone would have believed her).
** It's also a point in ''VideoGame/SilentHill3'', where you have to use the mix to kill some insects blocking your way. The bottles of both components give a clear warning not to mix one with the other, and when Heather does so, it takes ''seconds'' for the gas to send her running out of the room. To get back in there, you have to turn on the fans.
* Mercury gives up vapors at room temperature, which are invisible, odorless and can easily kill you. Mercury should never be spilled or held in open containers.
* [[http://en.wikipedia.org/wiki/Zyklon_B Zyklon B]], the gas used by ThoseWackyNazis in so many gas chambers during the Holocaust.
** Zyklon B is not a gas by itself, it's a way to store and transport the gas. It's absorbent diatomous earth permeated in the poisonous gas itself (hydrogen cyanide), which is released from it by heating.
* Semi-averted by the series of nerve agents. While they are a chemical weapon, their gaseous form is invisible to the naked eye. If there is a high enough concentration that you can actually see the nerve agents, you are probably too busy dying in a horribly painful manner to care.
* VX Gas is so potent that only 30 micrograms will cause lethality. To give you an idea on how small that is, find a pin and look at the tip. It only takes a droplet on that pin tip to kill one person.