Everything's more awesome when it's on fire. Unfortunately, in Real Life most ordinary objects, structures, and creatures are not particularly flammable. Even many of the materials that we keep around specifically for burning, such as charcoal and firewood, take time and effort to get a real blaze going. But hey, since when has reality gotten in the way of a good story?
In fiction, it's common for anything that might be even remotely flammable — or even some things that aren't — to behave as though they were soaked in kerosene. The merest touch of a flame, spark, or other source of ignition will set it ablaze, and it will never burn itself out but continue burning indefinitely, usually setting anything else it comes into contact with on fire with similar alacrity. One of the most common forms of this is when fire touches gasoline in open air, and the gas acts like napalm (in Real Life, gasoline needs to be mixed with oxygen in a precise ratio to burn, and won't do so very well in the open air).
This often overlaps with Hollywood Fire, creating a near-instant raging inferno that nevertheless leaves the heroes conveniently untouched. It also almost always applies to any creature with a weakness to fire, such as most types of undead.
- Vow of Nudity: Magically enforced by Spectra's cursed necklace; any clothes Spectra dons (except itself) instantly burst into flames and painfully destroy themselves.
- Asterix: The Secret of the Magic Potion: The forest of the Carnutes burns surprisingly easily after Sulfurix tosses his ablaze fur cape into it. One may wonder why it didn't burn before.
- Frozen: To expedite Anna's freezing to death, Hans extinguishes a fireplace fire by pouring a jug of water over it. Mere minutes later, Olaf attempts to relight it with a single lit twig, and it bursts instantly into vigorous life, with a prominent "whump" sound as if the wood had been doused in lighter fluid rather than water.
- Inverted in The Artist: When George burns the film reels, they take quite a while to get a good blaze going. However, since film of that era really was made of incendium (a.k.a. nitrate), it should have turned into a massive fire in seconds.
- Cinema Paradiso: A nitrate film fire destroys the titular cinema and renders its projectionist blind. In a later scene we're shown how new cellulose film does not present the same risk, and he laments that it came too late for him.
- In The Green Hornet Strikes Again!, the ocean liner "Paradise" must have been made from flash paper. In the time it takes the Hornet to force a one-page confession from a crook, a fire in one of the holds takes over most of the ship.
- In HOUBA! On the Trail of the Marsupilami, after General Pochero's Céline Dion live-sized dolls fall from their rotating pedestals, they start catching fire for no reason at all.
- Indiana Jones:
- In Raiders of the Lost Ark, Marian's bar catches fire incredibly quickly. Granted, it appears to be mostly wood construction, but unless her patrons make a habit of spilling whole bottles' worth of her very highest-proof spirits (most liquors are not flammable) absolutely everywhere to make the fire spread as quickly as it does, there's no reason the entire structure should have burned down other than Rule of Cool.
- It gets even more ridiculous in Indiana Jones and the Last Crusade when a similar scene (very small fire caused by a dropped cigarette lighter escalates comically quickly into a giant blaze) happens in a stone castle.
- The Lord of the Rings: The Ring Wraiths will burst into flames if they come in contact with a fire source. Aragorn uses this to an incredibly effective degree in The Fellowship of the Ring when he lights up half of them and hurls the torch so hard that it embeds into one's face. Doesn't really seem to deter them for long, though.
- In Star Wars: Revenge of the Sith, Obi-wan kills the cyborg General Grievous by using a discarded blaster to shoot Grievous' few remaining organic parts. He quickly catches on fire, and Grievous' face explodes.
- Twilight: Vampires seem to have varying degrees of flammability. In the first movie, the protagonists kill and burn a vampire in a large fire. In the third film, Edward throws a lighter on a recently killed vampire. Both methods of burning result in vampire flambé. Even the latter's clothing rapidly burns away.
- Dave Barry states in his home improvement parody book The Taming of the Screw that you can make softwoods (e.g. pine) burst into flames by merely dropping it. (In contrast, hardwoods are very safe, since they automatically extinguish themselves when you light them.)
- Game of Thrones:
- Jon Snow turns a wight into a walking bonfire in short order by smacking it around a little with a lit torch. Note that this is not some dried-out, thousand-year-old desiccated mummy, but a very fresh corpse that also happens to be frozen solid at the time.
- Being undead is not a prerequisite, either: when ranging beyond the wall, it's standard practice to burn all bodies in order to prevent them being raised in the first place. When we see this happen, it takes maybe 30 seconds to set a fresh corpse ablaze where it lies. Presumably the enormous funeral pyre used to cremate Khal Drogo was just for show, if bodies catch fire that easily.
- Stannis' supplies (and horses) in Season 5 appear to be Made of Incendium if the ease by which a handful of men can turn them into an uncontrollable inferno without anybody noticing until it's too late is any indication, leading some fans to speculate that it may have been an Inside Job by Melisandre (whose magic could have done so much more plausibly) aimed at making Stannis desperate enough to sacrifice his daughter to R'hllor.
- In "Book of the Stranger", the khals apparently hold their most important meetings in gasoline-soaked huts, if the ease with which Daenarys can set the place ablaze and kill them all is any indication.
- In iCarly, it's a Running Gag that Spencer can set anything on fire by accident, even things that shouldn't be flammable, even without using fire. Not only is everything made of incendium... it's magic, too. In one episode, he sets a fire extinguisher on fire.
- Kamen Rider: In Kamen Rider 555, defeated Orphnochs erupt into blue fire and then crumple into dust.
- In the Star Trek: Deep Space Nine episode "Progress", Kira barely has to touch Mullibok's house with a lit torch to set it to burning merrily.
- AdventureQuest: Werewolves originally had a large weakness to fire. Eventually, each update made them even weaker to the point to where they would burn from the weakest fire sources. Even normal wolves aren't spared from the blazing weakness.
- BowMaster: In the third game, killing an enemy with fire results in it turning slowly into ash from the feet up, leaving only a charred skeleton wearing a helmet.
- Evolve has several fires burning in the ruined structures of its maps that never die down and don't seem to have any fuel source.
- Half-Life The headcrab zombies burn pretty easily in the sequel, though everything else does as well. Road flares and even small debris fires will send even heavily armored Combine troops aflame.
- Left 4 Dead series: The Infected can be lit up from somewhat understandable sources, such as Molotov cocktails and to a stretch, incendiary ammo. However, it's most obvious when the zombies toast themselves doing relatively not-deadly things such as vaulting over burn barrels or stepping on smoldering coals. Said things at their WORST would inflict minor burning and welting. The playable "Special Infected" can be set ablaze by small sources as well, and will actively burn for up to an entire minute (depending on HP) before suddenly dropping dead; rendered to a charred heap.
- Enemies in the game adaptation of The Thing will ignite at small fire sources. They may light each other on fire if they collide with one another, and may even light the player up as well.
- The Legend of Zelda:
- While donning the Zora's mask in The Legend of Zelda: Majora's Mask, contact with any fire source will immediately kill you, and the last few seconds before continuing show Zora Link bursting into flames and collapsing.
- The Keese in The Legend of Zelda: Ocarina of Time are extremely flammable. In fact, they'll often deliberately light themselves on fire to do more damage to the player!
- Mass Effect 2 and Mass Effect 3: Any unshielded organic enemy will light up and immolate when hit with Incendiary Ammo or the Incinerate tech attack. Never mind that they might be wearing ablative body armor, have chitinous armor or a cybernetic skin weave. They all go up in flames.
- In Overcooked!, if something on the stove burns, the fire quickly spreads to everything. Even the bare countertops burn as energetically as the charcolized remains of what's in your oven.
- Pretty much anything in Team Fortress 2 that does fire damage will instantly engulf the target in flame, although they'll self-extinguish in ten seconds or less. Oddly, though buildings visibly burn from any damage, they will never suffer "afterburn" damage.
- Sword Art Online Abridged: Whether it's lag-infested taverns, yandere-haunted workshops, stadiums filled with rioting fans, or a giant fucking goat demon rampaging against some salamanders, it's clear the game code for Sword Art Online and Alfheim Online is overly sensitive to immolating things under pressure.
- Played for Laughs in Futurama:
- In "Bendless Love", Doctor Zoidberg tries to re-coil a slinky after Bender has straightened it into a straight wire. It goes down two steps, falls over and then bursts into flame.
- Lampshaded in "The Deep South", where Zoidberg claims a giant conch shell on the bottom of the ocean as his home. Later in the episode, they return to it to find it's burned down, leaving only a charred framework.
Zoidberg: How could this happen?!
Hermes: That's a very good question!
Bender: So that's where my cigar was.
Hermes: That just raises further questions!
- The Simpsons:
- In "Fear Of Flying", a flashback to Marge's childhood shows her playing with a toy airplane when it bursts into flames.
- In "Team Homer", Bart shows off a "Down With Homework" t-shirt in class, suddenly setting off a riot in which the students tip over Mrs. Krabappel's desk, which somehow sets on fire.
- In "Homer the Smithers", Homer, sitting in for Smithers while he's on vacation, tries to make breakfast for Montgomery Burns only to repeatedly set it on fire. Even when he pours a bowl of cornflakes and milk.
- SpongeBob SquarePants: One episode has a gag where Patchy leaves a note for SpongeBob, but the ink runs in the water. As SpongeBob notes, whoever wrote it clearly didn't consider the physical limitations of living underwater, and they might as well throw it into the fire…Which they do.
- Nitrate films (made prior to the introduction of Cellulose Triacetate (safety) film in 1948) had to be stored in thick-walled concrete bunkers because they were so flammable. This video shows some examples in its first 2 1/2 minutes, and an even more spectacular example starting at 4:25. Safety film is non-flammable. Get it hot enough and it will melt, but it won't burn easily, as this video shows.
- Hypergolic mixtures. They ignite on their own when mixed. The Trope Maker could be the T- and C-stoffs used on Me 163 Komet. The T-Stoff was concentrated hydrogen peroxide (a strong oxidizer) and C-stoff was a mix of methanol (fuel) and hydrazine (a strong reductant). When they were pumped in the reaction chamber of a Walther rocket engine, they ignited immediately and burned hot. No external flame or igniter was needed.
- The quote from the memoirs of John D. Clark, a research chemist employed by the US Navy's rocketry program from 1949 to 1970. One of the many challenges that the original "steely-eyed missile men" had to overcome was finding a fuel and an oxidiser that reacted energetically enough to put a given payload into the desired trajectory while still being stable enough to be stored without elaborate refrigeration arrangements or containers made of expensive specialist materials; another was finding the aforementioned hypergolic mixtures, which would immediately react when injected into the reaction chamber, rather than building up and then reacting.
[Chlorine trifluoride] is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water — with which it reacts explosively.— John Clark, Ignition
- Black powder, usually thought of as Made of Explodium, is actually this trope; it technically deflagrates (burns violently) rather than detonating. This is more apparent when slower-burning powder mixes are used, such as in portfires (basically black powder road flares), which are used to light cannon or firework fuses, burn extremely hot for several minutes each, and are basically impossible to put out once lit except by dunking them in water.
- The element fluorine sort of invokes this trope: it causes most everything else it comes into contact with to burn. It is the most chemically reactive of the elements, often creating high heat conditions during the very vigorous reaction. Chlorine trifluoride-based fire is almost impossible to put out.
- Obese human corpses. They contain so much fat that they cause a fire hazard in crematoriums. Most European crematoriums refuse to cremate any deceased who has weighed 130 kg or more in his or her life — they need to be interred, often with aid of a mobile crane as the caskets may be too heavy for human pallbearers. Several crematoriums have actually burned down due to a conflagration of a grease fire when an obese corpse has been cremated.