Tactical Door Use

Nearly all video game protagonists stand in awe, fear and wonder at the nigh-indestructible nature of the common wooden door. But what few of them realize is that their enemies also hold the same feelings of alien terror and incomprehension for them. In fact, most of them are even more afraid of these doors than the heroes are, because while it may be a pain in the neck for a hero to get one of them open, for the enemies such a feat is nearly impossible, even if said door has already been unlocked. Many of them lie awake at night in fear that they may have to face a hero who has actually figured that out, because such a hero will inevitably employ Tactical Door Use.

When the player is able to close and open doors at will, they have complete control over where their enemies can and cannot go. When chased by a massive mob of foes, all you have to do to get out of it is hide out in a closet until they give up. Additionally, clever door configurations can let the player turn an attack on all sides into a bottleneck assault they can easily deal with.

Needless to say, the games in which this trope appears tend to be Nintendo Hard or at least approaching it, as it takes a truly outmatched and desperate individual to see doors for the brilliant tactical instruments that they are.

A form of Insurmountable Waist-Height Fence from the AI's perspective, and usually an example of Hit-and-Run Tactics. See also Tae Kwon Door and Door Judo.

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Examples:

Action-Adventure

• ANNO: Mutationem: At The Consortium's Elaborate Underground Base, Ann comes across a large red sphere of corrupted energy that chases after her until she makes her through the door into the next area.
• Metroid:
  • You can often escape enemies chasing you by exiting through the door. They will not follow between rooms but sometimes might hit you a few times inside the door before you get the next one. Backing in-and-out of them is not so useful because walking through the doorway resets each room. The exception, however, is Space Pirates in Zero Mission, who can still follow you from room to room, keeping up the chase.
  • The SA-X in Metroid Fusion will chase the player between rooms as well. SA-X encounters are scripted events, however.
  • In the Metroid Prime series, Tallon IV Metroids will explode if you trick them into colliding with a door. It's especially useful in That One Room in the Impact Crater, which has a long slog up a bunch of platforms to reach the final boss while being constantly attacked by endlessly-respawning Fission Metroids, and there are no energy or save rooms. But there is a missile room partway up, so Samus can lure the Metroids to the doorway and kill them with impunity until her health is sufficiently restored.
• In the original The Legend of Zelda, no monsters or projectiles, except Blue Wizzrobes, can touch you while you're hiding in a doorway. Now, hiding in the door also prevents you from using any of your items, sword included, but at least you can wait until the monsters move into a more advantageous location. Doesn't work on bomb holes, however; as soon as you start to enter one, you automatically move all the way into the next room.

Action Games

• In Bonanza Bros., you can use the doors to knock out guards, but the same can be done to your character if you're not careful.
• In the arcade game Mappy, pictured above, your only defense against the cats chasing you is to open and close doors. For some reason, the cats knock themselves out if they open the door on the side of the knob, so the player can use doors strategically. Rainbow doors, which only the player and not the cats can open, unleashes a one-time shockwave that picks up any cat in its path and clears them off the screen temporarily.
• Monsters in Mystic Towers have sets of rooms that they're restricted to, but you can also, in some cases, press a button to close a door on them partway through their territory and lock them on one side. Unfortunately, there's not always a second way through, and you don't need to divide and conquer because there's only one monster per room anyway. So it's fine for catching your breath, but not much else.
• The Intellivision game Lock 'n' Chase was all over this one. The maze setup was a Pac-Man knock-off, but the player character locked the police (enemy) characters into corners or otherwise trapped them to buy some safety and score points.
• Hotline Miami makes judicious use of this trope, as opening a door into an enemy will stun the enemy. Given that the nature of the game is a Nintendo Hard instant-death fast-paced mixed melee/ranged deathmatch where you are frequently outgunned and always outnumbered, and killing enemies unstealthily will frequently cause more mooks than you can reasonably handle to rush the room, you will use this to your advantage.
  • There is also a mask in the game that will make a door hitting an enemy instantly lethal.
• Downplayed in Pac-Man, where ghosts are slowed down when they try to cross the Wrap Around tunnels.
• Punching doors in Mr. Shifty will send them flying into enemies.
• In Descent, the robot enemies cannot open doors for no explained reason (since you open doors by shooting them, and enemies can definitely shoot). Some levels have wide and lengthy sections without any doors, which becomes terrifying at higher difficulties. Averted in the sequel, where certain enemies can and do open doors to let other enemies in.

First-Person Shooters

• Call of Duty: Modern Warfare (2019): Most doors are now dynamic parts of the maps they are on, and can be opened and closed at will to gain or deny passage. They can be opened in either direction, which could help with ambushing one's enemies or setting up traps for the would-be intruders.
• This is a key tactic to surviving in the Left 4 Dead series, as infected cannot open doors normally; closing a door forces them to either find a way around or slowly bust it down. They can even be used as an impromptu shield to clear a room, by damaging them enough to break a hole in it and then shooting through that to hit infected, who are forced to break the door down fully before they can retaliate. The opening room of any given level can usually be completely cleared in this manner, as saferoom doors are indestructible to anything short of a Tank.
• Quite often in Halo one can back in and back out of the doorway, letting it take the enemies' shots.
• The Half-Life mod Cry of Fear uses the Resident Evil model, although more due to thematic reasons rather than technical limitations, as can be seen on rare occasions where an enemy will suddenly break down a door as you try to open it, incidentally connecting two sections of a level together.
• Doom: While monsters can open many doors, there are several ones they cannot (particularly ones requiring keycards or opened by switches, although these are not the only examples). Similarly, players can quickly open a door, shoot into the next room and close the door again as a means of slowly picking off opposition from behind cover (or inducing monster infighting as the monsters end up accidentally hitting their buddies with fireballs).
• SWAT 4 has literal tactical door use: you have items called tactical wedges that can hold a door shut. Very useful for preventing suspects from roaming around and sneaking up on you.
• The Pelagic II in Perfect Dark is made simple by standing in front of doors and sniping guards through the portholes. Although enemies can normally open doors, the AI doesn't understand how to shoot through small openings, and the guards become confused when they take damage from a room not immediately accessible to them.
• In Duke Nukem 3D, it is possible to take out the self-destructing Sentry Drones by closing a door in their "face" as they activate and approach you—it triggers their proximity sensors and makes them go boom.
• In Killing Floor, a lot of the maps have an abundance of doors to weld shut. This is usually used to channel a horde of enemies down a select number of paths so they won't all swarm the player, though sealing yourself in so that the enemies spend time battering the doors down is also an option. You can also lay a pipe bomb on the inside so that a large group gathers at the doorway before breaking through.
• None of the zombies in Dead Island know how to open doors. If there is a workbench and vending machine on one side, and a horde on the other, it can be easy to kill off the entire horde via a battle of attrition.

Platform Games

• In any Mario game with Luigi's ghosts in it, even though these translucent ghosts are probably top of the list of foes you'd expect to be able to float through doors, once you've opened a door they can't follow.
• In Tom and Jerry Chase, the doors in some stages can be used by the mice to stall the cat, or by the cat to trap the mice with it. Equipping the "You Shall Not Pass" perk card allows mice to turn this into Tae Kwon Door.

Real Time Strategy

• In Aliens: Dark Descent, your marines are exploring large, multi-room facilities in order to rescue civilians and clear out the alien infestation. Enemies can normally go through doors, but your marines can weld them shut (or cut them open again). If you seal off an entire room with welded doors, your squad can take a break and regroup, lowering their stress levels.
• For Warcraft III:
  • It's not actually used in the game (possibly because opening then closing a gate automatically restores the gate to maximum health), but many custom maps give you the ability to open and close gates at your convenience.
  • Because the computer ignores destructibles other than trees, and because of the game physics, parking a summoner next to a gate and casting the spell will result in the summon spawning on the other side of the gate. This greatly reduces the difficulty of dungeon crawls and other Baseless Mission scenarios, since you can now kite the enemy into getting whittled down by ranged units and spells before knocking down the gate to pass through.
• Zigzagged in StarCraft II. Many natural obstacles are present that can be used this way, but the AI will now attack them as well to open up units for attack. The Terran's Supply Depot building can be sunk into the ground and walked on, allowing for a variant of this trope (if the enemy is stupid enough to let his troops get separated).

Roguelikes

• Many creatures in Ancient Domains of Mystery are incapable of opening doors. If the randomly generated dungeon is kind to you, you might find a room that you can run to, close the door, and heal up. Opening up the door again gives you the benefit of fighting the monsters one on one as they come at you. With all the numerous items in the game, sometimes you can come across wands of door summoning, which creates a door for you. Doors can be destroyed, but most monsters don't have the capabilities to do so. Sentient creatures would sooner open the door than destroy it. However, whether enemies can eat through the walls surrounding the door is another matter altogether.
• In Angband, many low-level enemies, including notorious Explosive Breeders, can be trapped behind doors. Most later enemies can just bash down doors, though one can jam them with iron spikes to make that harder.
• In Dead Cells, doors can be open or closed, and enemies can hear you through closed doors, allowing players to kite foes through them. An additional use for doors, though, is by breaking them down, stunning foes directly on the other side. The crowbar item even gives you a few second of critical hits after you break one down.
• In Dungeons of Dredmor, doors separate every room from every other room. And with the exception of the locked ones you chose to kick down rather than unlock, all of them can be closed again with ease. Since this is a Roguelike game we're talking about, erecting an indestructible barrier between you and your enemies will very often save your life, especially if you encounter a dreaded Monster Zoo. (However, beware that there do exist enemies who hold the mystical power of opening closed doors...)
• In Duskers, this trope is vital for your survival, along with Thrown Out the Airlock. It is essentially Tactical Door Use: The Game.
• In Nethack, closing the door is useful for evading monsters that have no hands (thus, cannot open doors). Locking the door is safe against most other enemies. Exceptions include oozing and teleporting monsters, certain giants that break doors down, monsters with keys, and some bosses which can just open a locked door through magic.
• Pixel Dungeon may not have invincible doors, but whenever an enemy opens a door they leave themselves open to an ambush, which is 100% accurate and does bonus damage if certain weapons or subclasses are used. Closing doors also provides cover from projectile users.

Role-Playing Games

• Geneforge starts using this trope in the second game. The enemies you face are incapable of interacting with doors in any way, and what with doors being, well, doors, they're extremely plentiful, and on the higher difficulties they can be exceedingly useful.
• Subverted in The Elder Scrolls. Though the doors are indestructible, humanoid enemies are typically smart enough to turn the knob. Double Subverted in Morrowind, where casting a Lock spell fixes that problem. PC players in Morrowind, Oblivion, and Skyrim can also use console cheats to do the same thing. Additionally, open doors may provide cover when fighting enemy ranged attackers in an empty room, leading to a case of Concealment Equals Cover in cases where the door should not be able to stop an arrow or a spell.
• Fallout:
  • While the enemies in the isometric games can open doors, they cannot unlock them. Which means if you are going to be initiating a fight where the enemies are divided into different rooms, you can use your lockpicks to isolate them into neat little cells where you can brutally dispatch them at your leisure. You can also use this with undamaged force fields, and in the first game, at least, to protect your woefully fragile and suicidal companions from powerful enemies.
  • The creatures in Fallout 3 figured out doors. This allows the player, if fast enough, to set loose a Deathclaw on enemies hiding inside a structure. Or...innocent people inside. This turns into terrible options, however, if a bad thing breaks into a building and kills a quest giver.
• In the Retaliation add-on for Mass Effect 3 multiplayer, this option was added to the Firebase Reactor map. The players can now trap enemies inside the eponymous reactor by sealing its doors just as it is about to overheat, killing everyone still inside.
• Completely averted in Dark Souls. Either the enemies can just walk straight through after you, or it's a boss door and something worse is on the other side. If you're really unlucky, both.
• In Legend of Grimrock, a viable tactic to defeat powerful monsters is to open the door they are behind, attack once, and then immediately close the door again before they can strike. Monsters can't open doors, so it's just rinse and repeat.
• In the old computer game Dungeon Master, this trope is taken to its logical conclusion. Not only are monsters unable to open doors, allowing you to open the door, attack, and slam it shut again, all doors open and close vertically. This means you can lure a monster into the doorway and trigger the door, which will try to close, inflict heavy damage on the monster, rebound, try to close again, inflict more damage on the monster, and so on and so forth until the monster moves away from the doorway or is killed. It is often faster and more effective to crush monsters under doors while attacking them instead of engaging them in combat directly.
• Very effective version in Diablo I. Closing doors will stop certain demons in their tracks. Combine this with a grate nearby that allows you to shoot through to the other side of the door, and soon you've got a pile of dead demons lying on the other side of said door.
• Actually averted in the final boss battle for Eye of the Beholder 2, the dragon you have to fight will burn his way through the doors as you use them to try and block it until all the doors are destroyed so they're only of limited effectiveness.
• A rather infamous tactic in Phantasy Star Online; enemies are confined to the room that they spawn in and will not follow you through doors even if you can traverse through them at will. You can combine this with any kind of ranged weapon to mow down tough foes while in the safety of an adjacent room.

Simulation Games

• In FTL: Faster Than Light you can upgrade your ship's doors to be nigh-indestructible. If enemy boarders teleport onto your ship, just lock them out of your vital systems and open all doors between them and the vacuum of space...no more boarders.
  • The Advanced Edition introduced the Hacking Drone, which in addition to making a given system go haywire, locks the door to its room. Combining it with boarders allows the player to slaughter everyone inside while preventing them from fleeing to the medbay.
• In Dwarf Fortress the player can instantly lock or unlock any door in the fortress, without any dwarf under the player's control having to actually walk up to the door to effect the change. And any goblins sieging the fortress will instantly become aware of the change in the doors, even if they can't see the doors in question. Combine that with the fact that the goblins aren't that smart, and will always choose the shortest route possible into the fort, and the player can manipulate the goblins into marching back and forth across a Death Trap strewn corridor by repeatedly locking and unlocking a door. With clever use of Pressure Plates, this can even be automated.
• This is the easiest way to escape bees/wasps in the Animal Crossing games—find the nearest building and run like hell.
• In Space Station 13, this is the AI player's only weapon both for and against humans. Most crewmembers just treat it like a doorknob for places your laws don't say they can't go, but it can lock and shock doors freely depending on whether or not its laws allow it, and typically the only evidence it's permitted to tell the crew about traitors is whether or not the latter wants it to open the door to the Captain's Quarters. Some servers even allow it to crush people or vent the entire station in one button, though it's a quick way to get banned if you aren't a lawyer.
• Video Game/Valheim: The Stagbreaker is a ridiculously huge hammer that becomes a Game-Breaker in burial chambers, where enemies behind closed doors won't immediately attack. The Stagbreaker lets you deal area damage behind the door, killing the skeletons behind it and attracting others to the same spot, letting you flatten them with impunity.

Survival-Horror

• Resident Evil's early installments used this, with loading screens between rooms.
  • There are at least two instances of enemies attacking you through doors - a hunter attacks Chris through one in the REmake, and zombies shamble through one loading screen in Resident Evil 2.
  • Later games from Resident Evil 4 onward avert this with enemies who can get through doors even outside of scripted events, but they also gave you an advantage by allowing you to kick the doors open, stunning any enemies who were trying to break through on the other side.
  • In Resident Evil 2 (Remake), players can actually "hide" behind certain doors by standing behind them as they open. This trick is particularly useful against Mr. X, as he won't be able to realize he's been had until he's walked a fair distance from the doorway, allowing fleet-footed players to slink past him when being chased. It doesn't work if he's already in the room or opening said door before one could hide, however.
• This is a key survival tactic in Amnesia: The Dark Descent. Though the enemies can and will batter the doors down, blocking doors can give you crucial time to escape or find a good hiding place. And it gets used against you in one sequence where not only can your pursuer smash through doors rather quickly but you have a series of closed doors in your escape path, all of which need to be pulled inward to open in order to slow you down even more. Fortunately the monster can't climb the ladder that you use to escape at the end of the tunnel.
• Call of Cthulhu: Dark Corners of the Earth has you do this in an early sequence of the game, desperately locking doors behind you and trying to find a way out.
• Zig-zagged in Silent Hill 4. Regular enemies can be stymied (temporarily) in the few areas that have doors you can close behind you, but neither the Victims nor Walter are balked by silly things such as doors—in fact, Walter even chases you across screen transitions.
• This plus Resources Management Gameplay comprises the core gameplay behind Five Nights at Freddy's. The third game takes this trope further with the air vents that can be sealed off at various points.
• Project Zomboid: Zombies cannot open doors normally, unless you tweak the "Zombie Lore" in the settings so they become able to. So if you are being chased by a horde, closing a door behind you will at least give you a moment to catch your breath and think. You might be able to sneak out of the side window if they are busy, because once a zombie starts trying to break down a door, it takes a fair bit to distract them - and one banging down a door is fairly noisy so it is useful to keep them there too. For long-term fortification purposes, it is a good idea to board up all ground-floor doors and windows and dangle some rope from an upper-storey window, giving you a way in they cannot use. These doors become very hard to break down, so you have a good chance to brain them in from behind while they are focused.
  • A skilful tactic is the "door flash" technique, where doors to a room are quickly opened and shut to give a quick peek of what's on the other side without (hopefully) alerting any zombies on the other side. Even if there is a zombie right there when you do it, you can sometimes stop their deadly lunge. Learning the door flash is essential for scavenging and navigating urban areas with at least a modicum of safety.
• Siren 1: Shibito on patrol will notice if a door that was closed is now open and vice-versa, so it's best to leave doors in the same state you found them in to avoid setting anyone off and possibly being discovered. You can also lock some doors to slow Shibito down, though this isn't as useful since they can just break the door down if they need to and most doors that can be locked are to tiny shacks or other areas where that door is the only way in or out; locked doors are more of a hindrance to you than to them, since on the rare occasions they do it you have to look for a key or spend a lot of time working to unlock the door and leave yourself vulnerable. This is later expanded upon when the game introduces Dog and Spider Shibito, further-evolved forms that get back up much faster than regular Shibito as well as being able to respectively move faster and traverse walls; because they're hunched down on all fours, however, neither form can open doors, so a relatively easy way to deal with them is to lure them into a room with only one door, knock them out, then close the door while they're down.

Turn-Based Tactics

• X-COM plays with it. The doors cannot be locked, and both your men and aliens can get through them. However, doors can be used to hide or set up ambushes.
  • In X-COM: UFO Defense and XCOM Terror From The Deep, a door only closes if a unit goes through the threshold. The OpenXCom port makes opening and closing a door a contextual action, though the AI doesn't do it. Dangerously, automatic doors (like those found on UFOs) cannot be closed under any circumstances, but will automatically close at the end of the turn.
  • XCOM: Enemy Unknown: Regular doors can be bashed open by a running unit, or opened silently by placing the operative on the adjacent tile and clicking the door. The latter is a free action, and doesn't attract any attention, which is useful in multiplayer. Rolling shutters can only be opened with the second method. Also regardless of door type, you can't close it again.
  • XCOM 2's door usage works a lot like the prequel, with a few alterations: opening a door is an action that pops up at the bottom bar, and you can close doors back up to block sightlines. With the way Concealment works^*a concealed soldier is invisible to the enemy unit if there's cover between them and the alien, even if the soldier is inside the enemy detection radius, it makes quickly scouting the inside of an enclosed space very simple. To mind, running through a door is a hurried, noisy action, and as a result, automatically breaks concealment.
• The Jagged Alliance series is also in the same boat. Doors can be closed after you open it, and can hide you from enemies. However, keep in mind all enemies (as well as guards/militias and civilians) can open just about any door even if it is locked, and they seem to close the door immediately after opening it unless they are interrupted right after opening.
• Invisible, Inc.: Door management is extremely important in keeping your Alarm Level low, especially on higher difficulties:
  • Opening/closing a door that a guard can see will prompt them to leave their post to check it out. This is a standard way of setting up ambushes, and is covered in the tutorial level. Just make sure opening the door won't bring your agent into the guards' line-of-sight.
  • Closing a door behind your agents after they pass through it will reduce the risk of getting caught in guards' peripheral vision and accidental body discovery.
  • If a guard has gone into Hunting mode (read: they've made direct contact with the agents and are actively, permanently scouring for them) and you close a door in front of them, they'll subvert your tactic by simply kicking the door down, permanently ruining it.

Unsorted

• Empire Of The Overmind. Monsters can open doors but not unlock them. Certain locations have doors which can be closed and locked. If you can lure a monster into the location, you can go outside and close and lock the door, trapping the monster inside the area. One such location has a respawn point where monster re-appear after being killed. If you close and lock the door, you can kill the monsters and they'll respawn inside the room.
• Door Door, one of Square Enix's first games, was entirely about trapping enemies behind doors. Enemies would march right inside if a door was opened in the right direction, and any door they were trapped behind would never reopen.
• In Meritous, enemies cannot shoot at you if you are in another room. By taking advantage of the doors that separate rooms, you can either offensively use the barrier of a door to hit-and-run, or you can defensively retreat and evade from enemy attacks when they get too dense to dodge properly. It becomes a must in the lategame when enemies become more deadly.
• Similar to the Dwarf Fortress example above, dynamic Tower Defense games can be played this way. Players have to leave an opening so the oncoming creeps have a path from the start to the exit, but players can build the towers in a maze pattern with two exits, and by building and demolishing towers, can alternate which exit is open; this forces the creeps who were heading towards one exit, having to go back through the maze to reach the other exit, while being whittled down by the towers' cannons.
• In RuneScape, the Birthright of the Dwarves quest ends with a boss battle against the leader of the Red Axe]] and his right hand man atop the Red Axe palace. A common strategy in this fight is to separate one of the two using a door in order to take them down one at a time.
• In Among Us, Impostors can not only turn off the auto-open feature of a map's doors (forcing whoever's at a door to flip breakers to open it), they can close individual doors to trap Crewmates in a room, usually to either set them up to be killed or to try to frame them for a kill.

Wide Open Sandbox

• Minecraft zigzags this one. Wooden doors cannot be locked, while iron ones have one built in because they need power to open or close. Villagers can go through wooden doors at their leisure, sometimes making them Too Dumb to Live. Zombies alone of the hostile mobs can use doors... as in, they'll break down wooden doors given enough time (and only on the highest difficulty at that). One way around this is to place a door so it is actually open when in its "closed" state and closed when "open", the AI will not know what to do.
• In Foxhole, heavy gates can only be opened by your faction. Thus it's possible to escape enemies by closing the gate behind you, but you can also trap them within your fortifications.
• Terraria plays it straight most of the time. Zombies look like they try to break down doors, but they cannot. The exception is the rare Blood Moon event, when they can, but even then it takes minimal effort to lock them out anyway. Even a single block behind the door will make it impossible to open in that direction, thus preventing them from entering. Goblin Thieves in the Goblin Army event are slightly more annoying, as they actually break the door down rather than opening it, but it's still rather trivial to stop them.

Non-Video Game Examples

Anime & Manga

• JoJo's Bizarre Adventure:
  • Stardust Crusaders: When injured and chased by Enya's undead horde, Polnareff quickly runs to a nearby room and shuts the door thinking they'll be too mindless to open it.
  • Steel Ball Run: After Diego transforms into a raptor, Johnny and Gyro quickly run outside to hold the door while Diego has it ripped apart.
  • JoJolion: Fleeing from Kei's Born This Way, Josuke is hit with a blizzard attack after running to a nearby house and immediately shuts the door to stop the blizzard.

Comic Books

• In Sonic the Comic, when the Metallix Mark 3 pursues Sonic, Tails pressed the switch to close the door and Metallix was crushed beneath it.

Films — Animation

• The Super Mario Bros. Movie: While fleeing from a group of Dry Bones, Luigi runs towards a castle and shuts the entrance before they could catch him.

Films — Live-Action

• Scream: Ghostface has received his share of doors to the face.
• Terminator 2: Judgment Day: When being chased by high-security mental hospital orderlies, a hopelessly outnumbered Sarah Connor who moments prior had been feigning being heavily drugged, takes advantage of closing barred doors behind her to slow down her pursuers, who are forced to pull out their keys to unlock each door in turn. When she starts getting slowed down by having to do the same thing at the next several doors, she even breaks off the key in the lock from the other side to slow them down even more.
• Subverted in Jurassic Park.
  We should be okay... Unless they figure out how to open doors. *click*

Live-Action TV

• Carnival Row: Phil pins the Darkasher beneath a sliding metal door in the sewer tunnel.

Western Animation

• Aqua Teen Hunger Force: In "Vampirus", when killer vampires break into their house, the Aqua Teens shut themselves in Meatwad's room by blocking the door. Which didn't help since they had a hole in the roof, letting the vampires get through.
• Star Wars Rebels: The small crew of the Ghost often uses closing doors in order to put a barrier between themselves and approaching Imperial forces. On one occasion, this completely fails because Ezra had earlier cut a large hole in the door to get through it without having to crack the lock, meaning that when they try to use it to block their attackers the blaster bolts go right through the hole.

Real Life

• A real life example: if there's a fire inside a home or building, it is usually a good idea to close the doors behind you as you get out to safety. Closed doors can significantly slow down the spread of the fire since the fire has to eat through the door first before it can spread to other rooms. If a door is open, then there's nothing stopping the fire from spreading. Moreover, closing the door creates one less opening to vent new oxygen in to fuel the fire. Some larger buildings have doors specifically designed for just that purpose, out of material strong enough to actually withstand the fire until it runs out of oxygen, limiting the damage to a portion of the building. This is usually why building security can be extremely anal retentive about removing doorstops and keeping certain doors shut even though those doors don't pose any obvious security risk. Most people are quick to assume the security people are just being, well, anal.

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