Deadly Gas

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As under a green sea, I saw him drowning.

"The sickly sweet aroma spreads.
Its stagnant arms bring only harm,
Along with sluggish, looming dread."

— Agent 8 writing about the Toxic Mist, Splatoon 2: Octo Expansion

Lethal gas is found in many forms and in many environments. It is naturally found in many underground settings (in Real Life as well as in games, particularly near volcanoes) and is abundant in the atmosphere of many planets. Humans have used it as a weapon of war, a method of execution, and in certain historical mass death traps.

This gas often has a greenish color, which is more a case of Technicolor Science and Technicolor Toxin than of Truth in Television. Carbon monoxide for example is notoriously colorless, which necessitated the Canary in a Coal Mine to prevent workers from dying. While chlorine gas (used extensively in the First World War) is green, nerve gases have been the chemical weapon of choice since World War II (although chlorine still works quite well if your enemy isn't well supplied with protective equipment and has been used as recently as the ongoing Syrian Civil War) — these are colorless and odorless, 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 your skin. The TV series Breaking Bad depicts this very accurately — when Walt and Jesse manufacture crystal meth, they don not just respirators, but full coverage yellow hazmat suits because in reality, the fumes are not just toxic to inhale, they're toxic if they touch the skin too.

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 Oxygen Meter or Life Meter very rapidly.

Sister trope of Knockout Gas, the non-lethal alternative. Hand Sliding Down the Glass is a sub-trope, as victims will sometimes do this as they succumb.

This trope is always present in a Gas Chamber.

Works with their own subpages

1000 Ways to Die

Examples:

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Anime & Manga

Attack on Titan: This was part of the method used by the Marleyan military to transform the inhabitants of Ragako village in to Titans by spraying the village with gas laced with Zeke's spinal fluid, followed by him shouting to trigger their transformation. As it was not administered through syringe (like in Rod Reiss' case), it further explains why the Titans of Rakago came out so deformed.
Cells at Work: Bacteria!: The leader of the Clostridium perfingens bacteria makes no bones about his status as a "bad bacteria" or his intentions to expand his group's turf.: After the host body eats barely anything but meat for nearly a week straight, Clostridium and his gang of bad intestinal bacteria are able to produce a large amount of hydrogen sulfide gas (rotten egg-scented gas) to harm the good bacteria. This also ends up giving her (the host body) a severe case of foul-smelling flatulence.
Dr. STONE: One of the geographic features of Japan 3,700 years in the future is a large sulfuric lake, which is metaphorically personified as an enticing "Sulfur Fairy" which turns into a hideous melted corpse just when you're about to enter the clouds of hydrogen sulfide given off by the lake. Senku being who he is, he explains all the uses the the sulfur lake can have for them but warns that if they take even one breath of the hydrogen sulfide then they're dead. This actually turns out to be very useful later on as some of Tsukasa's mooks aren't aware of the sulfuric lake and Senku and the Ishigami villagers manage to trick them into running straight into a hydrogen sulfide cloud, killing them.
Gundam
- In the backstory of the original Mobile Suit Gundam (later detailed in Gundam: The Origin), Zeon gasses an entire space colony's population to death before dropping it on Earth.
- The Titans in Mobile Suit Zeta Gundam used poison gas on space colonies in an attempt to prevent them from 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.
JoJo's Bizarre Adventure:
- Golden Wind: Fugo's Purple Haze emits an airborne virus that rapidly consumes the flesh of anyone within a close radius.
- Stone Ocean: Weather Report's Stand is used to create oxygen, which is poisonous in large amounts.
- JoJolion: One of the A. Phex Brothers' Stand, Schott Key No. 2, constantly generates a deadly toxic gas. It's kept inside a soccer ball where the gas can't escape. The elder twin can use his Schott Key No. 1 while touching the ball to jettison some of the gas at their opponent.
Mazinger Z: When The Hero Kouji and a 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 Home Base 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.
This is one-off villain Mustard's Quirk in My Hero Academia. He's not immune to the gas he produces, so he has to wear a gas mask at all times while his power is in use. The gas also functions as a Living Motion Detector, allowing him to sense anyone moving through it in case they home in on his position.
Naruto: Boil Release is a Kekkei Genkai, the result of a mixture of Fire and Water Release. It produces corrosive gas powerful enough to melt an incomplete Susanoo, which has so far been shown as an indestructible armor. Mei Terumi, the Fifth Mizukage, has it, and it is also the signature power of the Fifth Tails, Kokuo.
One Piece:
- Magellan, Chief Warden of Impel Down. Thanks to his Venom-Venom Fruit, his body is made up of poison, and chlorine gas is his most-used type of deadly gas.
- And way down the Sorting Algorithm of Evil there was Don Krieg, who had poison gas canisters in his repertoire.
- The Punk Hazard arc features Caesar Clown, a chemical weapons expert who ate the Gas-Gas Fruit, which allows him to create, control, and turn his body into gas. As Luffy learned, immunity to poison isn't enough to protect against him, as Caesar can also remove oxygen to cause people to asphyxiate.
- Caesar also has a Blob Monster pet named 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.
- When the Beast Pirates attack Zou while looking for Raizo, the Mink Tribe manages to fight them off for 4 days by rotating between Inuarashi and the Musketeers fighting them during the day, and Nekomamushi and the Guardians fighting them during the night. On the fifth day, however, Jack (one of Kaido's right-hand men and the man leading the attack) loses his patience and breaks out a poison gas weapon that takes the Mink warriors out of commission. While he sets about to torture Inuarashi and Nekomamushi about Raizo's whereabouts, Doflamingo's defeat in Dressrosa and his subsequent arrest force Jack to leave Zou in order to attempt a rescue. Not long after his departure, half of the Straw Hats led by Sanji arrive to Zou while bringing Caesar as their prisoner, who quickly recognizes the poison gas as his own creation, dubbed "Koro" (derived from the Japanese word for "kill"). Sanji and Chopper are less than amused at the carnage left behind by yet another of Caesar's weapons, and violently coerce him into fixing the mess. Caesar reluctantly complies, and uses his Devil Fruit ability to synthesize a gas capable of neutralizing Koro, dubbed "Roko".
In Sailor Moon, or more precisely, Codename Sailor V, Sailor V (Minako) has the power to use this. She uses this against a group of mosquitoes in the Pets arc, using a low concentration, but could have brought the full force of the Venusian atmosphere, which means a pressure 92 times that of the atmosphere of Earth, at 460 degrees Celsius (800+ Fahrenheit), and almost entirely carbon dioxide which suffocates you, plus some sulphuric acid that would melt you down. Yikes.
In Saint Seiya, Piscis Aphrodite can use his poisoned roses to create something similar to this. He planted hundreds of said roses on a very long stairway that Seiya must go through to reach the Pope; since the air surrounding the stairway and the roses was heavily contaminated with poison, the already exhausted Seiya collapsed after breathing just a little dose of poisoned air... Only his Sexy Mentor Marin's Big Damn Heroes involving her Cool Mask managed to change things.
The later episodes of Transformers: Energon have glowing green "Energon gas".
The Wolf's Rain 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.

Art

Gassed shows the aftermath of a mustard gas attack during World War I. Soldiers blinded by the gas are being led to a field hospital by orderlies.

Comic Books

Arrowsmith's equivalent of mustard gas is a deadly gas that kills its victims and then raises their corpses as Artificial Zombies.
Batman: The Joker's "Joker Venom", which kills while making the victim laugh, is most often seen in gaseous form. This is most notably seen in The Dark Knight Returns, in which he kills an entire live TV studio with weird dolls that exhale Joker Gas.
Captain Marvel (Marvel Comics): Mar-Vell first battles Nitro when the latter steals a container of a deadly nerve gas called Compound 13, which Mar-Vell is exposed to while sealing the leaking container. Although he receives an antidote to save his life, the gas is later revealed to be carcinogenic, and Mar-Vell dies from cancer resulting from that exposure.
Diabolik is a prolific user of hydrogen cyanide in traps.
Femforce: In The Untold Origin of Femforce, the villainous Plant Person (and ally of the Nazis) Fungi launches a poison gas attack on an army camp just outside of Washington, D.C., using toxic spores known as 'Green Mist'. It is this attack that brings the founding members of Femforce together for the first time.
G.I. Joe: A Real American Hero (Marvel): In one issue of 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.
Group Of 7 A Most Secret Tale: On April 22nd, 1915, at 1700 hours (5:00 PM), the Germans unleashed a deadly gas on the battlefield in the Second Battle of Ypres, which smothered the Algerian forces and scattered the French forces.
Tintin: In Tintin in America, a gangster has Tintin gassed and thrown in the lake, but then realizes that his goons used Knockout Gas instead. They return to the lake, but by then, Tintin has returned to consciousness and gotten the drop on them.
In Ultimate Fantastic Four, the N-Zone's atmosphere is acidic.
Wonder Woman (1942):
- Aeropyramic gas, which burns oxygen out of the air and makes it unbreathable, makes an appearance in issue #23.
- The villain Nina Close is known as the Mask before her identity is revealed, due to her signature move of trapping her victims in masks designed to release deadly hydro-cyano gas into their mouths if a ransom isn't paid or if someone attempts to remove them.

Fan Works

In The Conversion Bureau: Cold War, the Soviet forces are given authorization to use VX nerve gas on a large platoon of Royal Guards in chapter 7.
Pink Cloud from the Fallout: Equestria universe is a potent blend of one-third nightmares, one-third Nausea Fuel, and one third Body Horror. It was used by the zebras to exterminate everypony in Canterlot, and it was powerful enough to kill Princess Luna outright and fatally injure Princess Celestia. In addition to being deadly if inhaled, it melts skin and melds it with anything it touches: floors, walls, benches, Power Armor, Pip-Bucks... It can penetrate even the tightest-sealed Stable or the most advanced environmental hazard suit. And to top it off, it reanimates its victims as nigh-immortal ghouls who mindlessly repeat their last day of life over and over again until their bodies fall apart.
- Fallout Equestria: Pink Eyes has a non-feral Canterlot Ghoul as the protagonist, and this one adheres closer to the Ghost People inspiration, being effectively a ghost miade of Pink Cloud inhabiting an enviromental protection suit. If the suit gets breached, the Pink Cloud inside spurts out and tends to liquify anything it touches.
- Fallout: Equestria - Project Horizons, the antagonist Sanguine is a non-feral Canterlot Ghoul who can spit out ghouts of Pink Cloud as a Breath Weapon.
In the Kim Possible fanfic An Old Foe Returns, Mastermind creates a version that would make simians smarter while numbing the minds of mankind. He would have succeeded if Ron hadn't tapped into his hidden genius.
In Shielded Under the Raptor Wing it's mentioned that EarthForce started using mustard gas almost immediately against the Minbari whenever the aliens attacked on the ground. In the ground battle seen on screen, however, they opted for an unspecified nerve gas. The Minbari, not being stupid, issued fully sealed combat uniforms to their infantrymen and vehicle crews, but sometimes the rookies would fail to keep protective equipment ready at all time, leading to their deaths and the capture of military equipment (it's shown that one Minbari tank was captured due the rookie crew not having protective equipment ready when EarthForce gassed their position).
In Worldwar: War of Equals 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.
Plan 7 of 9 from Outer Space. In Chapter XI, a Yellow Peril supervillain threatens to bombard the United States with the deadly Purple Rain.

Films — Animation

In 9, gas bombs were the main method used by the machines to kill all the humans.
In Fantastic Planet, this is the method used by the giants to exterminate the little people.
Once Upon a Forest has a group of forest animals face a threat of a crashed tanker truck that was carrying chlorine gas which starts spreading throughout the forest. It makes the youngest of them, Michelle very sick and kills her parents.

Films — Live-Action

The US Military eventually starts using some sort of nerve agent in 28 Weeks Later. However, like everything else it's done half-heartedly and proves to be ineffective at killing off the Infected.
The ABCs of Death: In the "F" segment, an earthquake unleashes a deadly gas that kills everyone in the school.
In The Assassination Bureau, General von Pinck is asphyxiated when his saber pierces one of the hydrogen balloons in the airship.
The RDA in Avatar uses tear gas before they cut down the tree's pylons with missiles. Not strictly lethal, but very unpleasant, and very visible.
- Contrariwise, Pandora's atmosphere is toxic to humans. 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. 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, and even getting a good lung full of the atmosphere seems to cause no lasting effects once a human gets back to breathing oxygen, so really, all those masks do is scrub out the extra unwanted crap from the atmosphere. There's actually a good bit of Artistic License – Chemistry involved in all of this, as both carbon dioxide and hydrogen sulfide are toxic to humans at the concentrations present in Pandora's atmosphere (the LC_LO for CO₂ is 9%, while for H₂S it's 0.08%, so the concentrations in the atmosphere are 2x and 12.5x the LC_LO, respectively). And even that's ignoring that both CO₂ and H₂S are acid gases, so they dissolve in mucous membranes (such as the eyes and lungs) to form acids, which can cause permanent damage to many vital organs even if it doesn't outright kill you. This means that even taking in one breath should have some serious consequences at least, if not instant death.
- None of which stops Colonel Quaritch from pursuing the heroes and taking several shots at them... and then remembers he's not wearing a mask when a (mask-wearing) soldier comes up and hands him one.
In Batman (1989), this is the Joker's favorite method of killing people, courtesy of the Smylex toxin. He does it twice, once in the museum where Bruce is supposed to meet Vicki, and once in the big parade scene with big parade-float balloons full of Smylex. Batman takes the balloons away in the Batwing and sends them well away from the city in order to stop him. The "gas masks protect against nerve gas" mistake occurs twice: first with Vicki Vale in the museum and again when Knox uses a filter mask during the balloon attack. This might be justified: Smylex affects the respiratory system and makes victims literally laugh themselves to death, so it might be more like a very potent allergenic agent than an actual neurotoxin.
Brass Target: A train transporting Nazi Gold seized by the US Army in the aftermath of World War II is stopped in a tunnel and its military police guard murdered with gas. It's all part of a conspiracy by high-ranking U.S. officers to steal the gold. You'd think they'd come up with more unobtrusive ways to plunder a defeated country.
In Close Encounters of the Third Kind, authorities use a cover-up story about a train crash unleashing deadly gas to force the evacuation of civilians from the Devil's Tower. Some caged birds which the protagonists bring along as coal-mine canaries are covertly sprayed with something from an aerosol can that kills them, thus "verifying" the gas's threat.
In Crime Doctor's Man Hunt, Natalie kills the two hoods trying to blackmail her by opening the valves on her gas fire, and them leaving them in the room to asphyxiate.
In Escape Room (2017), Conrad and Tabby are killed when the room they are in is filled an acidic gas that causes their flesh to dissolve.
In Hostile Waters, when nuclear missile fuel mixes with seawater, the result is a toxic and highly flammable gas.
James Bond
- Goldfinger has the titular villain using Delta Nine nerve gas to 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 can only tell that the gas is being used by the sound effect and affected people falling dead, which makes the Heel–Face Turn even easier to figure out).
- Thunderball: The imposter kills Major Derval with a pistol firing a spray of gamma gas, then later plugs a small cannister of the same gas into the oxygen supply of the crew of the Vulcan bomber he plans to steal, after first switching to a separate tank of oxygen he's brought on board with him.
- 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 die horribly.
- The Spy Who Loved Me: After capturing a submarine in a Mega-Maw Maneuver, the villains fire a hollow bolt through the hull and attach it to a tank of cyanide gas, giving those inside a choice of surrender or die.
Kong: Skull Island: One of the soldiers is carrying canisters of an unnamed toxic gas when the first Skullcrawler attacks. During the fight, the soldier is knocked down and the cannisters catch fire, causing them to explode. The resulting gas cloud forces the characters to scramble to escape it, but no one is actually killed by it.
Last Action Hero: Benedict and Vivalid plot to unlease nerve toxin against a rival mafia group at a funeral so they can wipe out them in one go. Jack and Danny manage to foil it though.
In The Man with Nine Lives, Dr. Kravaal mixes a beaker of deadly gas that he uses to try and hold the officials hostage. One of them knocks the flask from his hand, resulting in them all inhaling it. They stumble into the freezing chamber and become Locked in a Freezer. By a staggering coincidence, the gas they inhaled turns out to be the solution needed to turn them into Human Popsicles.
Late in Morning Departure, chlorine gas start leaking in the admidships next to Manson's bunk, killing him.
Played for Laughs in Murder by Death:
Jessica Marbles: I smell gas!
Miss Withers: I can't help it, I'm old.
Jessica Marbles: No, not that kind of gas. The kind that kills!
Miss Withers: Well, sometimes my gas...
In The Phantom Menace, 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. They're also shown later in the movie to have been carrying breathing apparatuses the entire time. Wait, what?
Phantom Soldiers opens with the titular Phantom Soldier squadron wiping out an entire village, and using gas to execute the survivors. Helps that the soldiers are Gas Mask Mooks themselves.
In Pursuit (1972), made from the Michael Crichton novel Binary (as John Lange), a psycho millionaire steals U.S. 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.
The Rock uses a real-life gas, VX. On the other hand, it is not glowing green, and it's a nerve agent, not a blister agent. So no, you don't die with your face melting off and your clothes smoking. Instead, your nerves stop working, resulting in paralysis. The rest is accurate, though.
Sir Arthur Conan Doyle's Sherlock Holmes: When Holmes and Watson sneak into the Big Bad's castle, they get sealed in a small room that starts to fill with a deadly gas.
In Teenage Mutant Ninja Turtles (2014), 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.
Trench 11: Chlorine is released into the tunnels and Berton and Meuller have to run for it, as they have no gasmasks.
Triassic World: The building's security system is designed to release a gas that will kill every living being in the building if the dinosaurs aren't returned to their holding cells within two hours. At the end of the movie, the gas is released, and the dinosaurs all collapse to the floor, dead.
The Wild Geese. As they're fighting a war with no Hague Convention, the mercenaries use cyanide gas to silently kill guards in their sleeping quarters.
Wonder Woman (2017) is set during World War I, when gas warfare was introduced to the world. Doctor Poison creates a gas that is deadlier than standard sulfur mustard gas (the most commonly used gas at the time), as it dissolves a gas mask by itself.

Literature

Animorphs: All Gleet Bio-Filters at Yeerk Pool entrances 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 Binary, the Big Bad plans to use a deadly binary nerve gas to wipe out an entire city.
The MacGuffin of The Chinatown Death Cloud Peril (a pulp-homage novel by Paul Malmont) is a US Army experimental poison gas left over from World War I. Its effects are not pretty.
In Dead Beat, the White Council has evacuated their wounded to a hospital in the Congo. The vampires 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 sarin gas. Tens of thousands of completely uninvolved mortals were wiped out, along with dozens of Council Wardens.
Dead Man's Land by Robert Ryan. During World War One, Dr. Watson inspects a stash of poison gas canisters as part of his investigation into several mysterious deaths. Shortly after this someone bars the doors to the barn he's just entered, shoves a dispersal hose under the doors and opens the valve, filling the barn with chlorine gas.
The horror novel Demonic Color by Pauline Dunn (which notoriously plagiarized large parts of Dean Koontz's Phantoms, as well as recycling chunks of Dunn's own earlier novel The Crawling Dark) is about a corrosive green gas plaguing a town. The cover shows two boys being skeletonized by the gas' effects.
In the Novelisation of Earthsearch, two crewmembers of the Challenger are captured by Grand Emperor Thorden, who decides they must be alien-created humanoids and pushes the Big Red Button to feed poison gas into their cell. At that moment, Challenger arrives in orbit threatening to carve up the entire planet with the asteroid defense lasers unless the captives are returned. Thorden quickly puts the ventilation fans in reverse and rushes in a medical team to revive them. Fortunately the heavier-than-air gas had not yet risen above floor level.
In Michael Slade's Ghoul, a paranoid bomber in London attempts to kill everyone in a theatre with this trope, which he planned to generate by incinerating a whole lot of PFOA-laden Teflon.
The 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.
The titular belt of "poisonous ether" in The Poison Belt. Turns out it's harmless.
The Saint encounters this a couple of times in his career. In The National Debt, the villain is going to use gas to wipe out a ship's crew; when Simon intervenes, he spares a small amount to create an improvised Gas Chamber Death Trap in a cellar. In Story of a Dead Man, the villain traps Simon and that episode's heroine in another cellar, then opens a valve of plain old heating gas.
In the Sherlock Holmes stories "The Adventure of the Devil's Foot" and "The Adventure of the Retired Colourman", Deadly Gas turns out to be the murder weapon.
Various kinds of deadly gas show up in Star Wars Legends.
- Wedge's Gamble has some Rogues being balked by a room flooded with Fex-M3d, which would bind to neuroreceptors and make them suffocate. Fortunately, it turns out that one of them doesn't need to breathe.
- Korfaise gas is a coolant used on YT-1300 ships like the Millennium Falcon. It's also dangerous to breathe, and in The Thrawn Trilogy Han Solo cuts the coolant lines on a YT-1300 to incapacitate the people inside.
- In Star Wars: Allegiance, the heroes find a wall with embedded canisters of acidic, corrosive 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 Galaxy of Fear: The Doomsday Ship has some such gas at his disposal, but holds off on using it because it would kill the heroes too quickly, which wouldn't be as much fun.
- Tales of the Bounty Hunters: The Rash Equilibrium between Bossk, Chenlambec, and Tinian includes Bossk secretly wiring a container of "obah gas" into their shuttle's ventilation system. On Chenlambec, it will just work as a Knockout Gas, but for Tinian, who is smaller, it will be permanently crippling. There's not much difference in the end, since Bossk intends to kill Chenlambec for his pelt as soon as he's incapacitated.
Super Minion: Nicole once called to warn the authorities about a dangerous breed of monster that had started showing up in the city's Absurdly-Spacious Sewer. She almost died, because their response was to flood the entire section with poison gas without warning her.
The Colin Forbes thriller Terminal opens with a woman fleeing a Swiss clinic, only to die within sight of the gate when she runs through a cloud of gas from a mortar shell that bursts in front of her. The Reveal is that the clinic is developing a nerve gas to protect Switzerland against a Soviet invasion, with the terminally-ill patients being used as human lab rats.
Vorkosigan Saga:
- In The Vor Game, 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.
The War of the Worlds (1898): The Martians 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 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.
Blaine the train from The Waste Lands releases this upon the citizens of Lud just before leaving the city. When we find out why, it's because they were boring to him.
Watership Down. Heeding the apocalyptic visions of Fiver, a small group of rabbits leave Saddleford warren. The other rabbits either don't believe him or figure the majority can survive any disaster by sitting tight underground. Then humans seeking to redevelop the area turn up, fill in the rabbit holes and pump poison gas into the warren. The rabbits get the full horrific story when a mere two survivors turn up at Watership Down halfway through the novel.
In Wilder Girls, Headmistress locks all the girls in the music room and releases poison gas, turning the room into an effective Gas Chamber and killing some of the younger girls.
The Witch of Knightcharm: An evil Wizarding School requires all its students to complete a lethal obstacle course before they can become full students. On the day of the competition, the death traps in the course are changed out from the practice ones, and one of the new traps includes a room where the air suddenly becomes so thick that it turns into an unbreathable gas.
Worldwar: The militaries of Earth begin using mustard gas against the invading Race, who have difficulty responding to it because they've never had to deal with such things before and are slow to adapt, haphazardly retrofitting captured gas masks to their physiology.
In Z for Zachariah, nerve gas is used alongside a lot of literal Depopulation Bombs, causing a Class 2, possibly borderline Class 3 Apocalypse How.

Live-Action TV

24 had a number of canisters of this as a MacGuffin. 24 being 24, there is no instantly-effective antidote, no "opening the vents instantly makes the area safe again," and no "it gets stopped just before it's released." A lot of people, including some fairly major characters, die foaming at the mouth. Even in open air, breathing a little of the stuff will put you in a bad way but it's not certain death (as in, already-on-site medics who know exactly what to do can save you. There's no Fight Off the Kryptonite with Heroic Willpower with this stuff - at all.)
In The Adventures of Superman episode "Tomb of Zaharan", the gas intended to revive Lois' memory is poisonous, making the titular room a Gas Chamber.
Babylon Berlin features a cargo train importing (what seems to be) pesticide from Soviet Russia, It turns out that one car is actually filled with gold bars, while the other ones are smuggling military-grade poison gas to be used in a right-wing insurrection, which at one point poisons several characters and kills a Red Shirt.
One of the best Death Trap scenarios in Batman (1966) is when the Dynamic Duo are captured and challenged to avoid drowning in an industrial smokestack for period of time by the Joker. However, the Joker double-crosses them by filling the smokestack with a deadly heavier than air gas, noting "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."
Giles, Buffy and Willow almost get gassed in the Buffy the Vampire Slayer episode "Out of Mind, Out of Sight" 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.
Cannon: In "The Nowhere Man", Cannon has to find a stolen cannister of nerve gas that has been hidden somewhere in Los Angeles and that is set to be released at 7 pm.
Doctor Who:
- Shows up fairly frequently in the Classic Series; "Underworld" and "The Caves of Androzani" are two examples. The Fifth Doctor serial "Planet of Fire" inverts the trope by focusing on a gas with particularly healthful properties.
- "The Sun Makers": The Collector (actually a Starfish Alien disguised as a human) gloats about how he intends to end the revolt the Doctor has stirred up. The Doctor is currently being held at gunpoint by a guard.
  Collector: The sprinklers will release dianene, a deadly poison. Within ten seconds, everyone in the City will be dead.
  The Doctor: Except you.
  Collector: Exactly. I do not breathe air.
  The Doctor: No, but this chap at my shoulder, he breathes air.
- "Gridlock" 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 Giant Alien Crabs like it just fine.
- "The Sound of Drums": The Master kills off his annoying cabinet this way.
- "The Sontaran Stratagem"/"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 but which will nurture billions of Sontaran clone warriors.
Farscape: Instead of deadly gas, the Scarrans in The Peacekeeper Wars use a paralyzing gas. Scorpius notes that they use this on subjects they wish to dissect... while they're still alive.
FBI: Most Wanted: In "The Man Without a Country", fugitive-of-the-week Trofim Sarkov releases chlorine gas on a New York subway train.
In the Foyle's War episode "Bad Blood", an old comrade of DCS Foyle's recounts his experience with chlorine gas during the First World War, and how its traumatic effects still linger decades later. Thematic parallels are drawn to the germ warfare of the episode.
In the Fringe episode "The Bishop Revival", we have a 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 crowning moment of badassery, Walter displays his hatred of Nazis by coldly re-designing the same toxic gas to only kill the creepy Nazi guy. At a crowded peace summit no less.
Gotham Knights (2023): In "Under Pressure" Mayor Hill is murdered by the Court of Owls using poison gas in his car once he's for bungling the orders which they gave him.
Harrow: In "Ne Puero Gladium" ("Don't Give a Sword to a Boy"), Harrow investigates when two separate cases of death from chlorine gas poisoning happen in the same suburb on the same day.
Occurs in Helix
- In the pilot, CDC team leader Alan is frightened that Knock Out Gas released into the air vents will have this effect on his brother Peter, a research scientist infected with The Virus who has holed up in Air Vent Passageways in the Research, Inc. where he works. Alan needn't have worried, the halothane 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 Meat Moss from an infected monkey blood sample.
Immortal Xavier St. Cloud on 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 WW1 battlefield, killing everyone except immortal Duncan-but can't behead him before immortal Darius shows up and he scurries off.
The Return of Ultraman "Poison Gas Monster Appears!" dealt with Japanese usage of it in World War 2 in the form of a poisonous kaiju named Mogunezun, whose toxic breath is strengthened when it consumes leftover canisters of mustard gas illegally dumped by the Imperial Japanese Army. Kishida also gets a bit of involvement when he is devastated to learn that his family had been involved in the criminal acts committed with chemical weapons during the war.
In Stargate SG-1 we see this being used by the heroes, with the Tok'ra developing symbiote poison that dispersed as a gas. The U.S. military stockpiled a large amount in case of an invasion of Earth, only for the Trust to get their hands on some and subsequently kill untold numbers of innocent Jaffa in gas attacks on Goa'uld controlled worlds.
Star Trek: Picard: In "The Impossible Box", Narek modifies his tan zhekran (a Romulan puzzle box) so that it emits a red, poisonous gas that will kill Soji.
One That Mitchell and Webb Look sketch had 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 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.
True Lies: "Independent Dependents" has an arms manufacturing company's headquarters seized by some armed men, with it being revealed they had made nerve gas with the attackers planning to sell this on the black market. It's tested on one unfortunate hostage, who dies very quickly.

At the end of the first episode of Walking with Beasts, an earthquake shakes loose a massive bubble of carbon dioxide from beneath the region's lake. The gas sweeps through the surrounding Eocene jungle, killing any animal caught in its path (fortunately, the protagonist Leptictidium family are spared because they were upwind of the lake). This was Truth in Television, being a realistic depiction of a limnic eruption, which likely occurred periodically in the region the episode is set.
At least one The Young Indiana Jones Chronicles episode depicts a poison gas attack in terrifying detail. Other World War I-era episodes mention poison gas as well.

Music

Played for Laughs in the Flight of the Conchords song "Robots", set in Humanity's Wake after a Robot War:
We used poisonous gases (with traces of lead)
And we poisoned their asses (actually their lungs)
Sabaton:
- Several songs from The Great War Concept Album based on World War I reference the use of poison gas during the war. In particular "The Attack of the Dead Men" tells the story of Russian soldiers who were thought to have been killed by the poison, charging through a wave of gas at the Germans without gas masks.
- The song "Father" from the EP "Weapons of the Modern Age" is about Fritz Haber, the father of chemical warfare. The song abhors him for his "dark creation," but points out that he also worked on chemical fertilizers, making it difficult to judge the man. It also subtly alludes to the future applications of his work in the last verse.
The Talking Heads song "Air", from Fear of Music, is a particularly paranoid example. It could be a metaphor, but if taken literally, then it's from the point of view of a someone convinced that perfectly ordinary air "can hurt you, too".

Roleplay

Carina Appelbaum from v2 of Open Blue included vials of deadly gas amongst her many other mysterious chemical weapons, which explained why the crew and marines on her ship all wore gas masks.

Tabletop Games

Chemical weapons aren't commonly used in BattleTech, but there have been a few high-profile incidents:
- During the 4th Succession War, Hanse Davion famously used a chemical weapon known as Green Smoke against the Capellan Confederation. Green Smoke is harmless to humans, but it's extremely corrosive against the Triple Strength Myomer that the Capellans were using to give their Battlemechs improved speed and melee combat ability. And the only reason they were using it was because it was a Flawed Prototype that he'd tricked them into stealing so that they would use it and have an Archilles Heel he could exploit that they didn't know about.
- The Knights of the Inner Sphere, an elite unit that promoted valor and honorable conduct was famously killed off by a massive gas attack in the early years of the Word of Blake Jihad.
Dungeons & Dragons:
- Numerous spells exist to produce poison gases, ranging from the nausea-inducing Stinking Cloud to the extremely lethal Cloudkill, which in some editions can kill weak victims with No Saving Throw.
- Several mundane poisons can be delivered in gaseous form, such as Burnt Othur Fumes and Insanity Mist, which attack the body and mind respectively.
- The 1^st-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.
- A number of monsters have innate toxic gas attacks. The two best known ones are iron golems, which can produce a Cloudkill-like cloud of gas around their bodies, and green dragons, whose breath weapon is a cloud of poisonous chlorine gas (except in 3rd Edition, when poison didn't deal hit point damage so their breath weapon was a cloud of Hollywood Acid instead).
Exalted: Smoke, one of the elements of Autochthon, consists of horrifically toxic and corrosive fumes and is defined by its ability to destroy matter and kill living things. In its natural state, the Elemental Pole of Smoke serves as Autochthon's stomach, where scrap, waste and broken machinery are disposed of and broken down for reuse, but it also serves as a powerful way of scouring corrupted areas of his body from taint and gremlin infestations. The primary Lesser Elemental Dragon of Smoke, known as the Shogun of Genocide, is wholly dedicated to his role as an eradicator of life and can kill entire cities with the fumes of his passing.
In Flying Circus, poison gas is a weapon that both NPCs and PCs can deploy in combat, with the technology lingering from its use in the Great War. This hazard is prominent in the Poisoned Cities, where exposure to their pervasive fog result in progressively dangerous effects.
Games Workshop games:
- Warhammer 40,000:
  - The Astra Militarum have the Bane Wolf, a variant of the Hellhound flame tank, that fires a cloud of toxic chemicals capable of killing almost all infantry in a single blast.
  - The specialist Death Guard Sorcerers known as Malignant Plaguecasters are living links to the Garden of Nurgle. Every breath that the Plaguecaster takes fills the air with the noxious gasses of the Plague God's blighted realm. The 8th Edition rules represent this with the 'Pestilential Fallout' ability that will cause mortal wounds on any enemy close to the Malignant Plaguecaster whenever he successfully manifests a psychic power.
- Necromunda:
  - The Pollution result on the 1st Edition Campaign Events Table saw sections of the underhive filled with poisonous fumes from heavy discharges of toxic waste. The in-game effect of this event was to make tunnels and vents (territories that allowed gangs to set up fighters outside their deployment zone) unusable until the gas cleared.
  - 3rd Edition Escher gangs have access to the 'Nightshade' chem-thrower. Developed from the gas injectors used in House Escher's gene-labs, the chem-thrower is able to fill a corridor with clouds of chemical fog. The exact nature of the gas emitted by the chem-thrower varies from the relatively mild choke gas to insidious bio-toxins that attack the target's cellular structure, liquefying their flesh and internal organs. In-game chem-throwers are a deadly weapon that causes has a chance to inflict an Injury against an opponent without any saves and ignores their Wounds characteristic but can be resisted with respirators.
- Kharadron Overlords in Warhammer: Age of Sigmar have alchemists (called Aetherkhemists) whose main armament is an atomizer that slings clouds of various toxic gasses at whatever's threatening them. The sheer number of attacks can lead to entire squads getting gassed by a single one of them if you're lucky, and armor will not help much. There are also Balebreath masks, which will let heroes give heavy metal poisoning to any close-by enemies with a breath, and one of the City-Ports has the Breath of Morgrim artifact, which is the same but scaled to Ironclad's figurehead size.
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.
Shadowrun has two types of nerve gas: Green Ring 3 (from Real Life) and Seven-7, a fictional gas that can penetrate normal chemsuit protection.
Traveller: Several adventures in Supplement 6 76 Patrons involve PC attempts to acquire nerve gas produced by the Mega-Corp Schunamann und Sohn, AG.
In Vampire: The Requiem, the "Brothers of Ypres" Bloodline are descended from a World War I veteran who became a vampire amid a gas attack and developed Poisonous Person powers as a result. Their signature Discipline "Asphyx" lets them exhale clouds of poisonous gas and even transform into a toxic cloud.

Video Games

1916 - Der Unbekannte Krieg: To win the game, the soldier needs to reach the ladder to get out of the trenches. Said ladder is on the other side of a cloud of poisonous gas. The soldier needs a gas mask to get through it.
The original Alone in the Dark (1992) has a smoking parlor where the smoke will drain Carnby's health unless you extinguish the ashtray with a water jug.
ANNO: Mutationem: In Freeway 42's lab area, Ann finds the path blocked by a haze of toxic gas that'll immediately drain her health if she steps close, then having to activate the ventilation system to dispel the gas to get by.
ARK: Survival Evolved: Some features of the in-game world are filled with poisonous gas — on the default map of "The Island", the Swamp Dungeon is the key example, and the Aberration DLC adds a resource which is gathered from places that will occasionally emit toxic gases. The player can craft gas masks to counter these.
Ashes 2063: In Afterglow, part of the quest in the second hub is getting through a network of tunnels that have been automatically sealed due to a leak of several different toxic gasses. Scav has a gas mask that he always wears, but NPC conversation advises that just that won't be enough — a fully sealed hazmat suit is needed to brave the gas. As per the usual trope, once you get inside the contaminated area, it's entirely taken over by a green miasma that goes away once you activate the ventilation system override.
Assassin's Creed Rogue: Shay gets two types of gas grenades, Sleep and Berserk. As the name suggests, sleep gas is nonlethal, but berserk gas drives anyone who breathes it to a homicidal rage before causing rapid death. Also, Hope lays a trap for Shay in Sequence Six involving a warehouse rigged to fill with toxic gas at the turn of a crank.
Green gas makes players faint in Backyard Football.
Banjo-Tooie:
- Glitter Gulch Mine has a couple caves filled with green gas that depletes your air meter as if you're underwater.
- A couple of minigames in Grunty Industries will leak a suffocating gas if you botch them.
- One area inside a lava-filled cave in Hailfire Peaks is apparently full of noxious fumes, even though nothing is visible, as you'll lose air when you're in the room.
- Inside the cheese wedge of Cloud Cuckooland, apparently the smell is so bad that Banjo loses air, albeit a lot slower than in other instances of deadly gas.
- The HAG 1 releases a purple gas described as "cyanide and mustard gas flavor" at a certain point near the end of the Final Boss fight, limiting the amount of time you have left to beat Gruntilda.
  Gruntilda: Mmmm, cyanide and mustard gas flavor. My favorite!
Battleborn:
- Pendles' smoke bombs and Miasma ultimate involve the use of poisonous gas.
- Between the phases of Geoff's boss fight, the fumigation systems in the buildings he resides in are needed to be activated in order to release a gas that's normally used to drive out Bliss bugs. While Geoff is a Spider Tank, he thinks he's an actual giant spider and thus is driven out into the open by the gas. That being said, the gas is lethal to players.
Phosgene gas can be used in Battlefield 1's multiplayer. Players exposed to it have their health drained unless they put on a gas mask, which restricts their vision and hearing and prevents them from using their gun's sights. It also serves as an Achilles' Heel for some elite classes that are unable to equip a gas mask.
The Intruder Excluder level in Battletoads has traps that shoot small puffs of gas, instantly fatal.
In BioShock, Ryan kills off the vegetation in Arcadia with a yellow-brown herbicide then uses a similarly colored gas to kill Julie Langford.
Bravely Default 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 We Have Reserves, as he doesn't feel any guilt over the massive friendly fire the weapon causes.
In Breath of Fire: Dragon Quarter, after Ryu, Nina, and Lin return to the End Sector Borough to find three Rangers have ambushed them with a tank of poison gas.
The Ploughman and Chuffer "chemical projectors" in Brigador launch canisters that release "tubarão", a highly-corrosive, pale-white gas that dissolves structures, vehicles, and people alike. Bits of lore mention it being used in an incident known as the "Moerbeke Rain", after which miltants rounded up the scientists who created the gas and exposed them to it. They're said to have found with "insides turned to paste".
Call of Duty:
- Call of Duty: Black Ops 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, and planned by Dragovich to be released all over the United States. It's available as a tactical grenade in multiplayer, though it's nerfed to an incapacitant rather than instant death. It also appears in Call of Duty: Black Ops II in its full strength, manufactured by the Coalescence Corporation.
- Call of Duty: Modern Warfare 3 also has deadly green gas used on the battlefield. Makarov's men use dirty bombs in most major European cities, crippling the nations and paving the way for Russian invasion.
- Call of Duty: Advanced Warfare 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.
- Call of Duty: Modern Warfare (2019) has an unspecified gas used by General Barkov on Urzikstani civillians. In Warzone, this gas is said to be called Nova-4. It is significantly weaker than its Black Ops counterpart — however, it can still kill people in a few minutes.
- Subverted in the campaign for Call of Duty: Black Ops Cold War, in which Nova-6 exists, but only in a liquid form. Played straight, however, in its Call of Duty: Zombies mode, which features a new Nova variant called Nova-5 in the map DIE Maschine. It is completely non-lethal to humans but lethal to zombies.
This pops up a few times in The Cat Lady in the form of the deadly hydrogen sulfide. Mitzi's boyfriend uses it to kill himself, Susan uses it to kill the second Parasite, and the Eye of Adam uses it to attempt to kill Susan and Mitzi, claiming his own father's life in the process.
Caves of Qud has Corrosive Gas Generation as a possible mutation you can start the game with, and that other mutates can sometimes have. It lets the mutant spew out a great cloud of acidic gas (that they're immune to) for a few turns, which slowly spreads out and dissipates. The great thing about the mutation is enemies don't even need to breathe; the acid is so ridiculously corrosive it will eat through solid rock, so it both affects robots and plants and lets you tunnel through solid rock and walls. Allies aren't Friendly Fireproof, however, so you're on your own if you want to be a walking caustic sauna.
In Code Vein, the city in which the game takes place is flooded with miasma that accelerates bloodthirst and causes revenants to frenzy and become Lost, requiring specialized masks to filter it out of the air while exploring. It has no impact on gameplay, but is a focal point of the story (in that the player character can revive mistle, which can purify it) and crops up twice in cutscenes:
- The first happens not long after the game begins, in which a Lost attacks your current partner, Oliver, and damages his mask. He frenzies quickly, becoming the first boss.
- The second happens during a flashback revolving around events before the game. While fighting the Queen, the player character has their mask knocked off, getting a lungful of the miasma (complete with pained gasps and screams and clutching their throat), and appears to almost frenzy not long after, forcing Jack to kill them.
Command & Conquer:
- In Command & Conquer: Tiberian Sun, the Brotherhood of Nod weaponizes Tiberium in the form of a Chemical Missile, which detonates over the target area and saturates it with noxious clouds of highly corrosive gas. Its effects on infantry are... unsettling, to say the least.
- Before that, the Covert Ops addon for Command & Conquer: Tiberian Dawn had Chemical Troopers, a variation on the normal Flamethrower infantry who sprayed Tiberium gas, instantly fatal to any non-Chemical Trooper infantry. They reappear as enemies in Command & Conquer: Renegade, and the protagonist can use their gun.
- Command & Conquer: Generals: The GLA Toxin Tractor fires a stream of liquid anthrax (among other horrible things) that kill infantry very quickly. If fired into a garrisoned building, the liquid becomes a gas that instantly kills everything inside.
- Command & Conquer: Red Alert: In the first Soviet mission briefing, Stalin's inner circle are discussing the use of a poison gas on a town full of unwilling test subjects.
In Conker: Live & Reloaded, the gas grenade, when thrown, expels a cloud of poisonous gas, blinding and damaging anyone caught in the cloud.
Crystalis has an entire swamp filled with toxic gas. If you don't have a gas mask, you'll probably die before you reach the town hidden inside because of how rapidly it drains your Hit Points.
In Dark Devotion, the Pestilential Idol is a grenade which produces a cloud of toxic green gas when thrown. You can also obtain a spell book that creates such a cloud in your immediate vicinity.
The Plague Doctor in Darkest Dungeon, when not stabbing things with a surgical knife, tends to use gas grenades that inflict some of the game's nastiest hero-applied Damage Over Time. The gas plumes from one skill even form little skulls just to make it clear how dangerous it is.
The Dark Souls games have several of these as spells, Colour-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 color. There are also spells that generate clouds of yellow gas that do no damage but grievously damage the equipment of anyone passing through.
Dead Island 2: While the game's primary poison vector, Caustic-X is utilized more often in a liquid form, a Superior-tier ranged-weapon mod causes the death of a zombie to generate a gas cloud of Caustic-X that has the same effect on its victims: dissolving flesh right off the bone.
The Dead Mines: The player character is sent into an abandoned mine leaking toxic gas to the surface.
In Dead Space, one mission has Isaac fighting his way through the ship's hydroponics lab, killing necromorphs that are poisoning the atmosphere. He can survive due to his air-tight engineering suit, designed to operate in vacuum.
Deus Ex Universe:
- Greenish poison gas — and it's always greenish poison gas — is quite common in Deus Ex. It's available in movable/puncturable barrels, for a little variety from the usual kind, as well as gas grenades. At one point, you can play with some in the ventilation system and gas a whole facility of people.
- The green poison gas returns in Deus Ex: Human Revolution, 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).
Diablo III: Do not stand in Ghom's gas attack, because other than the fact that it deals significant amounts of damage per second, ew.
Divinity: Original Sin II:
- Poison clouds can be created by magic, grenades, and Trick Arrows; they inflict both Poison elemental damage and the Poisoned status, which causes further damage over time.
- Taken to its logical conclusion with Deathfog, which instantly kills any living character who enters it, ignoring any protective gear, Protective Charms, or poison immunity.
Doom³ 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 when you finally hit the "Vent Gas" switch, at which point it is instantly drained from the entire location and ceases being harmful. The Mars base must have some powerful gas vents.
In Dragon Age II, 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.
In Dragon Quest IV, there's a yellowish gas coming out of Mamon mine because that's where Estark is buried. While it makes the locals sick and eventually kills them, it has no effects on player characters.
In Eastward, the MIASMA is a dark fog that instantly kill anything and turns a surrounding area into a wasteland.
The last stage of Enemy Front have the Germans using Mustard gas to take down the rest of the partisans, you included. Said gas is depicted as a green fog that blurs your vision if you're caught in it, besides draining your health.
In The Elder Scrolls IV: Oblivion, vents of poisonous gas are among the many Death Traps to be found in Ayleid ruins, still discharging their fumes after thousands of years abandoned.
IG-88 in Empire at War: 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 EverQuest, the gods created a poison gas (the "Greenmist") to wipe out the Shissar.
Fallout:
- Fallout 3, Fallout: New Vegas, and Fallout 4 have stagnate pools of watery fallout that are signaled by their noxious fumes; while the fumes don't do anything, the radiation will poison you.
- In Fallout: New Vegas: Dead Money, the Sierra Madre is contaminated by the Cloud, a highly toxic red smog that also corrodes metal. It's able to penetrate the hazard suits that were (possibly) meant to protect people from the Cloud but sealed them in, forcing them to mutate into the Ghost People. On Hardcore mode, it slowly saps the Courier's HP outdoors, with more concentrated pockets causing faster health loss, as if the DLC wasn't hard enough.
Final Fantasy:
- In Final Fantasy VII, Tifa is nearly executed this way.
- In Final Fantasy Crystal Chronicles, the plot is about removing miasma (deadly purple gas) from the world.
- Late in Final Fantasy XIV: Stormblood, the Garlean Empire restarts developing a chemical weapon called "Black Rose", a lethal gas that kills by completely halting the flow of aether in all living things. Gaius van Baelsar, the original Big Bad of A Realm Reborn, had its production halted because it was far too deadly a weapon, one more fit for genocide than conquest. The Ascians restarted its production, ostensibly as a means of quelling rebellion, but in truth to further their own dark goals. As we learn later in Shadowbringers from information gleaned from a Bad Future, the destruction of the world of The First would cause a massive influx of light aether that would make Black Rose more potent, such that it would poison the entire world of Hydaelyn. Thankfully, not only does the world of the First survive, but Zenos has the gas destroyed so it doesn't interfere with his rematch with the Warrior of Light.
Foxhole has green ash grenades, a deadly poison gas. Exposure will kill you in about three seconds if you don't have a gas mask to protect yourself.
GoldenEye (1997) 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.
Harvest Moon: 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 Hexen, the Flechette item works differently depending on your character class. If playing as a Cleric dropping a Flechette creates a cloud of deadly gas that will severely damage anything trying to walk through it (including your character). Also, certain levels contain special mushrooms that emitted deadly gas. The mushrooms are covered in green pustules, make weird squeaking noises, and release the gas when damaged.
In Hollow Knight, the Volatile Mosskin and Fungified Husk enemies release largish clouds of toxic gas around them as their primary attack, and both also explode into a cloud of toxic gas shortly after being killed.
inFAMOUS: First Light: After Fetch has outlived her usefulness to Shane, he traps her in a building and starts pumping in poisonous gas.
Fetch: Poison gas? You pussy.
Shane: Well, can you blame me? It's not like shooting you to death has worked out for anyone.
One of the mortar weapons in Interstate '76 is the Chemical Mortar, which upon hitting the ground releases a cloud of gas that will automatically kill the driver of any vehicle that passes through it. Unfortunately, because mortars are almost impossible to aim and A.I.-controlled foes will automatically dodge incoming mortar rounds, it's very much a Cool, but Inefficient weapon: it's more likely to kill you than an enemy (since if you're driving fast, the shell will come down right in front of you).
Iron Storm, being an Alternate History FPS that extends WWI-era fighting and technology many years after the real world's WWI had ended, naturally features mustard gas grenades.
The Jagged Alliance 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
In The King of Fighters '95, poisonous gas makes an appearance... but only in cut scenes, as Rugal uses sleeping gas to kidnap the KoF champions and bring them to his presence.
In KZ Manager you must buy Zyklon B to gas your inmates.
The Legend of Zelda:
- The Legend of Zelda: The Wind Waker: Although not itself deadly, there is a purple poison gas that temporarily disables Link's ability to attack or use items, and there are usually enemies in the gas. Later, there are purple flying skulls with the same ability.
- The Legend of Zelda: Twilight Princess has one area with a deadly purple gas/mist that can be temporarily locally dispelled by waving a lantern about.
- The Legend of Zelda: Spirit Tracks: Stagnox's main defense for its abdomen is its toxic gas, especially during the first stage of the fight against it.
Horrible Gas in LittleBigPlanet. 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 electrified materials and the plasma balls of the Metal Gear Solid pack are just as lethal. Fire, on the other hand, takes two hits to kill a Sackperson.
The gas you can throw in MAG is substantially less dangerous than the other examples on this page, but it's effective as an area denial weapon.
In an old Apple ][ text adventure game with graphical aid, Mask Of The Sun, 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.
Samara's recruitment mission in Mass Effect 2 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 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 Game Over.
The Metal Gear series often will fill rooms with poison gas, which necessitates either very brief stays or a gas mask.
Metroid Prime Trilogy:
- Metroid Prime:
  - Two new enemies introduced in this game are Blastcaps and Puffers, which upon exploding release green gas that is harmful to Samus until it dissipates: light green for the former, dark green for the latter. Blastcaps are rooted in place, but Puffers float around the room.
  - The Ventilation Shaft in Phazon Mines gets filled with toxic gas once you near its exit for the first time, due to holes in the ceiling that perpetually spawn Puffers. The fans aren't running, so the room will remain full of gas until you find the panel to scan to turn them on. You'll need the Power Bombs for that.
- Metroid Prime 2: Echoes:
  - Three marines in one early room succumbed to an industrial-grade pesticide when a gas trap was engaged to kill some indigenous creatures. However, Samus' basic suit is enough to shield her from the poison.
  - Dark Aether's entire atmosphere, as well as the gas that Emperor Ing's second form releases into the room.
In Mr. Driller, drilling into "X" blocks will cover the player character in a toxic gas that robs them of 20% of their Oxygen Meter.
The main area of the Twin Labyrinths in La-Mulana has a deadly gas 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.
The New Order Last Days Of Europe: One of the many things that turn the Republic of Komi into one of the most volatile warlord states in the shattered remains of the Soviet Union is that the capital of Syktyvkar has massive stockpiles of chemical weaponry that the various cliques are fighting over as they fight for control of the nation. Usage after leadership is settled varies; the more good-hearted leaders only touch it in emergencies when the core republic is directly under attack, others are a little more indiscriminate, and the batshit insane Sergei Taboritsky will use them liberally, think they're not enough, and commission even worse gases until much of the Russian wilderness is turned into a poisoned wasteland.
No One Lives Forever has cyanide gas, which gives you hallucinations while draining your Hit Points. Oh, and it looks green. The cyanide bullets have the same effect.
Both damage-dealing Aeromancy psionics in Odyssey: The Legend of Nemesis create clouds of poison gas, rather than being straight-up Blow You Away as the name would imply.
In Onimusha 3: Demon Siege, Jacques gets trapped in a room that quickly fills up with toxic gas and soon loses consciousness, until his son Henri manages to relay on how to escape the room and shut off the gas.
Green gas barriers are a standard obstacle in the Overlord series, usually put in place to keep you from advancing too far until you've gotten your Green Minions back.
In Parasite Eve 2, Aya is trapped in a sterilization room where gaseous chemicals are released, slowly draining her HP unless she jumps in the garbage chute to escape. It's used again later 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 Game Over.
The outer edges of Ichiban in Party Animals has green gas that will kill players who linger in it for more than a couple of seconds, explaining why knocking players off the platform is one way to win on this map. Over time, the gas wafts into the arena, shrinking the battlefield.
Perfect Dark
- In the original game, 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, the scientists kind of forgot that they're still in the room as well.
- Perfect Dark Zero: In the 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.
Pikmin:
- Played with. The planet that the games take place on is extremely heavily hinted to be Earth and is noted to have an oxygen-rich atmosphere. Problem is, the player characters come from a species to whom oxygen is highly toxic, so they must remain in their environment suits at all times. Further toyed with in Pikmin 3, which introduces a second alien species who can tolerate oxygen, but there's too much of it around on the Pikmin world (three times as much as their homeworld), so, while they might survive, leaving their environment suits would have bad effects on them regardless.
- Pikmin 2: Poison takes the form of clouds of purple mist, which lie close to the ground and will suffocate any Pikmin who stumbles into them, except for the poison-immune White Pikmin (captains, who are protected by their full-body spacesuits, are also safe). This gas is released by half-buried pipes found scattered around the game and is also produced by a number of enemies, such as the flatulent doodlebugs, the poison-venting munge dweevils, or the Titan Dweevil boss by means of one of the weapons it carries about.
Pokémon: 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 perfectly harmless. Not to mention there's also a move specifically named "Poison Gas". It poisons things.
Portal: The second game, and all the side media like the Ratman comic, firmly establish Deadly Neurotoxin as GLaDOS' weapon of choice.
- In the final level of Portal, after you 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 Schrödinger's Cat), which she then used to kill them.
- Portal 2:
  - Neurotoxin 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 Fridge Logic: Why does it take the neurotoxin six minutes to kill you in the first game, but only three seconds in the second game?
  - Part of Chapter 5 involves shutting down the production facility so that GLaDOS will be deprived of it as a weapon. It then makes a reappearance, albeit briefly, in the Final Boss fight.
  - The Perpetual Testing Initiative DLC mentions an alternate Earth's governing body, a sentient cloud which can come in under doors and leech the skin off people.
The Powder Toy has caustic gas, which dissolves everything it touches and is sometimes used in bombs.
[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 (however, he's apparently growing resistant to it).
- [PROTOTYPE 2] has a Suspiciously Similar Substitute for Bloodtox called Whitelight. Unfortunately, Mercer wised up this time around and pulled a switcharoo so that the gas is completely harmless to infected but kills or zombifies humans. In their infinite wisdom, Blackwatch continues to stockpile the stuff in their bases ("bioweapons", see) so if you're feeling especially dickish you can toss some containers around the streets and cause your own localized zombie outbreak.
In Ratchet & Clank (2002), 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 Ratchet: Deadlocked, the atmosphere is apparently capable of sustaining life again.
Resident Evil 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 until after some arbitrary time limit passes, at which point it'll kill 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 this Let's Play says: "Diffusion? Who needs it?"
- In Resident Evil: Outbreak 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.
Rise of the Triad has several rooms fill up with deadly gas shortly after you walk in. There's always at least one gas mask somewhere in the room and picking it up will protect you from dying. Since the enemies are never clever enough to do the same, you can then just wait for them to die. The gas drains away by itself after a minute.
RuneScape: In "The Path of Glouphrie", brightly colored poison gas is used as part of a Death Trap.
The Borely Haunted Mansion in Silent Hill 3. 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.
Sniper Elite V2 features the all-too-real nerve agent, Tabun, as a major plot point. Wolff and the Soviets plot to fill the last V2 with it and stage a German "last resort" attack on London.
Sonic the Hedgehog:
- Sonic 3 & 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 Super/Hyper Sonic isn't immune to. The only way to dispel the cloud is to destroy the Toxomister that made it.
- Sonic Chronicles: The Dark Brotherhood has gas that simply acts like a wall in terms of gameplay... except to characters like Big.
Star Fox Adventures has gas in a few places that make Fox fall over in his Oxygen Meter 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.
- 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.
In one level of Star Trek: Elite Force 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 Alexander Munro, have to use your 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.
Star Wars Legends:
- Gas traps are a common obstacle in Star Wars: Knights of the Old Republic. You too can break into computers to use the gas systems against your enemies. Even weirder is the Star Wars: The Old Republic'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.
- In Star Wars: Republic Commando, the second run through the detention block level ends with you defeating the ambush with the anti-jailbreak system, which releases deadly gas in a rather fruity pink color. Fortunately, your squad is immune since the designers remembered why Storm/Clonetroopers are Faceless Mooks and have your armor 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.
Stubbs the Zombie: 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.
In The Suffering, one of the bosses, a former warden responsible for gas executions and killed himself in the gas chamber, is an anthropomorphic, poisonous gas cloud, 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 to let the people he kills know that they are about to die.
Super Mario Bros.:
- Super Mario 64 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.
- The spin-off Super Princess Peach has rooms in Fury Volcano that are filled with a deadly smoke. Standing in the smoke hurts Peach gradually, but she can use her Joy Vibe to blow it away, though the smoke will slowly build up again.
Some enemies in The Swindle deploy clouds of poisonous gas, either on death or as bombs. When you get a lungful, the screen goes really blurry, and if you don't get to the escape pod quickly enough, you die.
The Gas Grenade from Syphon Filter. In the first game, it's the only way to beat the Final Boss, who's wearing full-body armor that makes him Nigh-Invulnerable but still requires him to breathe.
The caves of Sylph's Mountain in Tales of Phantasia are flooded with miasma that damages you as you walk through it. You have to push the boulders around to plug its source.
TimeSplitters Future Perfect features a gas-chamber deathtrap on Khallos' train. Lampshaded by Harry Tipper:
"Aw bummer! Green gas! That's the worst kind!"
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 Life Meter-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.
The first Ubersoldier has a stage where you sabotage a German chemical plant with tanks that leaks deadly toxic gas that the game reminds you to stay away from.
Unbound Saga have areas clouded in green "Radiation vapor", which you must escape within a given time limit before the vapor drains you of your health. Said areas tend to contain either Beast Man or mutant mooks, immune to the radiation.
Gas in Warframe is one of the six composite elements, gotten through combining Heat and Toxin. It can cause enemies to be covered in a toxic fog that damages others nearby, making it very useful in huge crowds. The dart gun Zakti is the only weapon in the game that does Gas damage normally, and with its darts exploding into gas clouds that can cause more gas clouds, it's an area-of-effect monster.
Waxworks (1992) features a gas trap in the Ancient Egypt level, as well as a plant that spews acidic gas at you in the mines level, the latter of which also gives you a death screen treating you to the sight of your own eye melting down your face as you choke on your blood.
In the white chamber, it's possible to die from toxic gasses that result from not getting rid of the dead body inside the fridge.
Nerve gas is a tactical aid option in multiplayer matches of World in Conflict. True to real life, it's horribly lethal to infantry while leaving structures and vehicles unharmed, which makes it useful for digging infantry out of buildings which you want to use for yourself.
In The World Is Not Enough, there is one point in the game when security cameras 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.
This is somewhat common in World of Warcraft. You would be surprised how many people don't understand how to not stand in it. It's also weaponized by the Forsaken in the form of 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.
Worms features the worlds least-deadly deadly gas, as it doesn't actually kill affected worms, just slowly reducing their life points to 1.
In Ys II: Ancient Ys Vanished – The Final Chapter, one area is filled with toxic gas, which the Roda Tree Leaf protects against.
Zombie Army Trilogy: The second season DLC trio in Zombie Army 4: Dead War features a zeppelin loaded with Blood Bombs; bombs that release a gas that turns the living into zombies. Your characters, and the resistance base, witness the effects in Alpine Blitz, but manage to evade the gas in the airtight Safe Room.

Web Animation

In one Homestar Runner 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.

Webcomics

Champions of Far'aus: Sea serpent Serpentus's paralytic venom, when sprayed like mist, falls somewhere between this, The Paralyzer, and Knockout Gas, as Skye loses feeling in her legs and passes out within a few moments of breathing it in, and comments made by Serpentus heavily imply that prolonged exposure is lethal.
In Darths & Droids, following the plot of the Star Wars prequel trilogy, the room where the characters were supposed to hold some negotiation is filled with toxic gas.^note The players continue talking in character, while holding their breath.
The Land of Tombs and Xenon in 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).
In Yokoka's Quest, Yokoka and Mao's original home had toxic air, which has given them an immunity to poison through long exposure.

Web Original

In The Salvation War, 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.
SCP Foundation 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.
During the Pandoric War in Look to the West, an experiment in creating tear gas accidentally creates a nerve gas. The industrialist responsible is horrified, and tries to keep the discovery out of the hands of his own government by giving the information about it to a friend, then disappearing, unaware that the friend is a Societist, and has his own plans for it.
In The Fire Never Dies, the Reds make use of chemical weapons in several key battles, such as Erlanger, Wilmington, and Washington. While their weapons are described as less sophisticated than their European counterparts, the Whites never manage to get proper countermeasures in place due to their mediocre industrial base.

Western Animation

In Arcane: League of Legends, Silco threatens the Chembarons with a cylinder full of poison gas.
Avatar: The Last Airbender: Avatar Roku, Aang's predecessor as Avatar, died when he received a faceful of toxic volcanic gas.
In one episode of My Life as a Teenage Robot, Jenny and Killgore end up in a unknown location and try to escape. Upon entering a new room, poisonous gas seeps in, causing Killgore to panic until Jenny points out that since they're robots, the gas won't have any effect on them.
The New Adventures of Superman: In "Luthor's Lethal Laser", Luthor and Brainiac attempt to kill a shrunken Superman by fumigating him with kryptonite gas.
Private Snafu: In "Gas", Snafu is stalked by a sentient cloud of poison gas: hampered by his extremely poor gas mask protocol.
One of the many types of gases used by the vile borg, Noxious in Skysurfer Strike Force.
Star Wars: The Clone Wars: In "Dooku Captured" falling rocks in the cave system open fissures in the floor that release toxic gas, nearly killing Anakin and Obi-Wan before Ahsoka and Rex blow open the entrance.
In Teenage Mutant Ninja Turtles (2012), the yellow gas on the Kraang's planet that they recreate in the TCRI building is toxic to Earth beings.
- Conversely, to a Triceraton, Earth's oxygenated atmosphere acts as such, though it's slow-acting. The victim suffers from hallucinations, but given enough time, breathing it would likely cause permanent brain and lung damage and eventual death.
The Venture Bros.: In Season 6, Rusty, Billy, and White create "God-Gas" which is intended to inflict mind control on anyone who inhales it. The gas ends up causing the affected to experience realistic hallucinations that drives them mad.
Voltron: Legendary Defender: Thaseryx is filled with nitrade gas.
Done retroactively in one episode of Young Justice (2010). Poison Ivy has a plant with flowers that emit aerosolized Joker Venom, which is seen infecting people. A later episode confirms that in the Young Justice setting, Joker Venom is lethal.

Real Life

All of the halogens have this tendency, and are a rare case of Technicolor Toxin in 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 properly secured in an ampoule, or you're already dead. The heavier halogens are non-gaseous, but they are extremely volatile and the vapours are almost as nasty. Bromine produces a rich reddish-brown gas that's the same colour as its liquid form, while Iodine sublimates into a bright violet gas and melts into a liquid of the same colour when sufficiently heated.
- 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. And how about the toothpaste in your bathroom, or the fluoride ions in the water you drink? Without those, your teeth would be in considerably worse shape; something that's normally very dangerous is helping make your life that little bit better, thanks to the wonders of modern chemistry.
- Note: do NOT try to overheat or burn teflon. It will release deadly gases, not fluorine itself but some particularly vile fluor-compounds. Among these are hydrofluoric acid vapour (see below) as well as perfluoroisobutylene, which is ten times more toxic than phosgene (a war gas).
- Even fluorine pales in comparison to 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 ''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 Nazi Germany weaponized it: 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.
Carbon monoxide (CO). It kills by attaching itself to hemoglobin, substituting oxygen. Carbon monoxide is generated by burning carbon-containing substances in insufficient amount of air for enough oxygen to form carbon dioxide. Such event can occur by closing the chimney plates before the embers have cooled down. Carbon monoxide is colourless, odourless and tasteless, and can be detected only by special means, such as fire warning gear. It is used as the iron ore reduction agent in Steel Mill as it will strip the ferric and ferrous oxides the oxygen and form metallic iron. Unfortunately, carbon monoxide poisoning due to ruptured tube or leaking valve is an all too common way to die in a Steel Mill.
A good number of toxic gases were used as weapons in World War I along with chlorine – phosgene, lewisite, mustard gas, among others. Adolf Hitler experienced this personally and refused to allow their use during World War II (at least not on the battlefield), 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 Knockout Gas 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 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.)
Hydrogen sulphide is highly toxic, causing instant collapse with loss of breathing at 1000 ppm, while lower concentrations can have some nasty side effects, such as eye irritation, headaches, nausea, coughing, shortness of breath, and irritability, even if they aren't deadly. During the Permian-Triassic extinction event, it seems that a severe anoxic event produced copious amounts of H₂S, which caused the extinction of 96% of all sea creatures and 70% of all land creatures. It's less likely to cause surprise poisonings than other, less toxic gases, though, due to its extremely strong smell ^note. However, at concentrations above 150 ppm, it paralyses the olfactory nerve, completely deadening the sense of smell (and for several days, by the way). So if you stop smelling it then you are either perfectly safe, because it has gone, 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 1000 Ways to Die 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 King of the Hill 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 Silent Hill 3, 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.
- A "mixture" like this was used as a murder method in a case from Case Closed. Except the victim, who was supposed to clean up her and her older sister/roommate/killer's bathroom with this poisonous mixture and die for it, purchased noticeably softer cleaners and averted the trope. The killer "had" to knock her sister out and kill her via staging a supposed Bath Suicide. It even gets lampshaded by Conan-as-Kogoro at the end.
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. In the event of a mercury spill, the proper course of action is to drop what you're doing and evacuate the area, then call authorities to have a hazmat team with proper equipment and training clean it up.
Zyklon B, manufactured by IG Farben, was the compound utilised in the four false 'shower' rooms of the Auschwitz-II/Birkenau extermination facility by Nazi Germany as part of their infamous Final Solution. The active ingredient is hydrogen cyanide, which is permeated in diatomous earth and released 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.
Although inert gases do not actively attack the respiratory system, they can still be dangerous enough to kill a person through oxygen deprivation. This is why you're supposed to evacuate the area after using a fire extinguisher containing carbon dioxide or most other gaseous extinguishants; they work by cutting off the fire's access to oxygen, and are equally good at cutting off your access to oxygen. (Ironically, halon [bromotrifluoromethane or bromochlorodifluoromethane] is actually the exception in this regard, despite the conspicuous warning signs saying not to hang around in a halon-protected area if the halon discharges. Halon works by breaking down into halogenated free radicals which inhibit the combustion reaction directly, even in the presence of oxygen; this makes it very useful for fighting fires in places that can't be immediately evacuated, like aircraft, spacecraft, tanks, and submarines, since it can be used in occupied compartments without the danger of asphyxiating the occupants. The warning signs are because halon has acute, though generally benign, effects on the central nervous system, and because the breakdown products produced when adding halon to a fire are somewhat toxic with prolonged exposure.)
Similarly, nitrogen itself is not toxic, but if it were to be introduced into an enclosed compartment with little to no ventilation at moderate or higher concentrations, it can displace the remaining oxygen in the space and cause death by asphyxiation. One example of this happened in the very first Space Shuttle mission in 1981, where two technicians walked into an area located in the Shuttle's Mobile Launcher Platform that happened to be pressurized with pure nitrogen as a precaution against a fire accident; the nitrogen lethally asphyxiated the two poor workers. The main problem is that, because you can breathe out the carbon dioxide normally, you won't notice you're asphyxiating until you collapse.
Even pure oxygen can kill a human if it is breathed in for longer periods of time, especially if it is pressurized.
Saddam Hussein used poison gas in his genocidal Al-Anfal campaign, making him the first dictator after Hitler to have perpetrated genocide with poison gas.
Chilean dictator Augusto Pinochet ordered his DINA to manufacture sarin gas, according to FBI reports.
In 1995 the Aum Shinrikyo cult released sarin gas into the Tokyo subway, with the hope that they would kill enough people to coerce the government into letting them take over. Fortunately only 13 people died despite the enclosed area and all the perpetrators were caught.

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