Safe room

"Safe house ahead!"

- Bill

Officially termed a safe room (also known as a safe house), this is the mission goal in both Left 4 Dead and Left 4 Dead 2 chapters save for finales. Once all Survivors are inside a safe room and have closed the door, the chapter's results scores will roll and the next chapter will load.

Appearance
A safe room is a barricaded room or building which enables Survivors to rest, heal and resupply themselves. In Campaign Mode, they also give teams a chance to take a break and discuss plans for the next chapter. Safe rooms are easily identified by red, heavily armored metal doors. Chapter ending doors are solid and have only a peephole. Chapter starting doors are fundamentally different in design, being locked with a crash-bar and featuring a large aperture window providing a wide field of view―and fire.

Safe rooms are extemporized from pre-Infection permanent structures (e.g. a hotel kitchen), from random opportunities (e.g. a railroad caboose) and by deliberate construction (e.g. the safe room at the end of the sky bridge at Metro International Airport.

All safe rooms are equipped with First-aid kits, ammunition, and weapons. Weaponry is usually of the Tier 1 class, but Tier 2 weapons will be supplied in those safe rooms prefacing final or second to last chapters. Occasionally, a safe room inventory will also offer Molotovs and Pipe Bombs.

All safe room walls bear graffiti left by previous Survivors. Valve stated in Left 4 Dead's commentary that the concept of safe room graffiti was intended to fill in some of the plot and contextual backstory that Left 4 Dead would otherwise lack.

Evidently, CEDA encouraged the construction of safe rooms. Multiple posters throughout the Left 4 Dead games carry instructions showing how to build a safe room. CEDA's checklist included the following:
 * An adequate supply of water
 * Non-perishable foods
 * A First Aid kit
 * A flashlight
 * Necessary prescription medicines

Another Checklist involves:
 * Seeking shelter underground in a windowless room
 * Ensuring all openings have been securely obstructed
 * Securing the room with plastic sheeting and duct tape
 * Listening to the radio for further instructions

Since these instructions are located in completed safe rooms it is impossible to say whether CEDA or uninfected local residents actually built specific safe rooms. Nevertheless, the standardized construction of safe room doors does suggest that CEDA had an inventory of these items on hand prior to the Infection, which they distributed quite freely once it became clear that orthodox quarantine measures were failing.

Tactics
As a general rule, the safe room is the only part of a map where Survivors are completely safe from Infected attack. However, if provoked and left to their own devices long enough, Common Infected can eventually break down a safe room door on any difficulty mode.

Door management is key factor in game play. If a door remains open, any Infected may enter the room until the door is finally closed. If an Infected horde is blocking the arc of a door's aperture, the door cannot be closed until this impediment is removed and the door's outline is picked out in white. Finally, if an Infected enters the safe room, it must be killed or pushed out of the room before the chapter will end and the next one can be loaded.

Common Infected who notice the Survivors inside will often try to reach into the safe room through the bars in the exit door. They usually pose no threat and can be disposed of very easily by gunfire or melee.

In Versus Mode, the safe room door will open automatically after a while if the Survivors delay their exit. Once it opens, it cannot be closed again.

The Survivors

 * Be proactive about the Infected outside. Shoot what is seen and clear the area for a safer, easier departure.
 * As soon as one Survivor leaves the safe room, the music cue will change, and the Special Infected will be allowed to spawn. Leave the safe room and start the chapter quickly. If Survivors dither in the safe room for a long time without attempting to leave, the Director will eventually spawn a Tank to destroy the door.
 * When in Versus mode, try to leave the starting safe house as soon as possible since wasting time gives extra time to the Infected to plan and launch a first strike. The longer a team lingers, the better the odds of the Infected mounting a well-coordinated first strike.
 * When in Versus, the safe room door will open automatically after about a minute, so it is better for a co-op team to form a plan quickly and get out into the open. When the door is opened, it is recommended that all Survivors leave the room quickly so that the Infected team will not be able to achieve what is referred to by the player community as "Insta-Spawn," the quick re-spawn of fallen player-controlled Special Infected.
 * In campaigns and in Left 4 Dead 2, safe room doors do not open automatically so players can take all the time they need.
 * The Witch has a nasty tendency to spawn very close to safe room entrances. The easy way to deal with this problem is to have the team open up on her simultaneously or let an auto-shotgunner sidle up and either Cr0wn her or let her have half a magazine on full auto. An entertaining alternative is to have a Survivor startle the Witch then run to the nearby safe room and close the door. Since the Witch cannot break down the door she will simply run away at this point and leave everybody free. (Note that this ploy does not work in Versus as the safe room door cannot be closed after being opened)
 * If faced with a Tank, running back into a safe room is questionable since AI Bot team members will not follow but will stand their ground and fight.
 * If closely pursued by a Tank, it may be possible for a player to run back to a safe room and close the door. However, there is some evidence to suggest that players who have tried this discover that either the door will not open or that it will not close.
 * On certain levels such as The Crane, Infected can reach through holes in the wall surrounding the safe room and do damage, so stay clear of these.
 * A common trick is to trap the Tank inside the chapter ending safe room and, since he cannot break the door down, he can be despatched at no risk by gunfire shot through the door or with a Molotov. This is extremely helpful online, especially on Versus mode, since it is relatively risk-free and a player's health status generates points at the end of each chapter.
 * This ploy can also be used to good effect in games on Hard or Expert difficulty. Let one Survivor lead the Tank into the safe room while other Survivors shut the door. This sacrifices the Survivor inside but keeps other teammates alive. The Survivor's inventory items will drop in the safe room while the recently deceased will respawn in the next chapter.
 * In Left 4 Dead 2, players should never run into a safe room thinking it is safe because the Director may decide to spawn a Special Infected or two inside (a rare glitch has even been seen where if both doors are closed but not everyone is inside yet, the Director may spawn a Special Infected out of sight on a two-story safe room, such as in the middle of Hard Rain).
 * Riverside First Church is the only Left 4 Dead chapter to feature a Special Infected regularly spawning inside a safe room, namely The Church Guy. On occasion, a Special Infected may spawn in a safe room and lie in wait for the Survivors.
 * Watch out for the window on the exit door, some Special Infected can attack through the window; however, the Special Infected are only allowed to spawn after someone has left the safe room:
 * Boomers can vomit through the window but the resultant horde can be easily defeated as long as the door is closed.
 * Smokers can attack the Survivor through the window.
 * Spitters can spit through the window.

The Infected

 * While the door cannot be breached, Infected can sneak in when the Survivors are nearing the goal. Often, one person will break away and attempt to run to the safe room, making themselves prime targets for the claws of a Hunter or the tongue of a Smoker.
 * The safe room is the last point where Infected can really team up on the Survivors. Make the most of the final point by organizing in front of the safe room, and then keeping one Infected inside the room for good measure. Try to position a Boomer outside to vomit or explode on your target, as the Horde that will quickly come will further slow the Survivors down. A Spitter can also spit in front of a safe room to delay the Survivors from getting inside (if they don't want to take damage), or into the safe rooms to force the Survivors to get out.
 * While the Infected cannot spawn until the Survivors exit the safe room, it also gives a good opportunity to organize a powerful first wave. Organize the Infected team early to hit them just as they are coming out. The sooner Survivors are hurt, the sooner Survivors will have to use their first-aid kits.
 * Try to hit the Survivors before they enter the safe room as a Tank, even if you spawn very close to the end. Even if the Horde is entering the safe room and have the Survivors occupied, the Survivors may try the trick stated above if they can, which you cannot escape.
 * If your team is skilled enough, try to keep Survivors in the beginning safe room. As long as one Survivor doesn't leave the safe room, you can respawn almost instantly. Also note if all the Survivors leave the safe room and go back in, this no longer works (this feature is not applied to Left 4 Dead 2).

No Mercy

 * The Apartments ― In the basement of an apartment block next to the subway.
 * The Subway ― Inside the store room of the pawn shop, presumably built by the shop's owner.
 * The Sewer ― In the staff lounge behind the hospital's main reception desk.
 * The Hospital ― In a temporary room in the construction site on the 28th floor of the hospital.

Crash Course

 * The Alleys ― In the center of a warehouse.

Death Toll

 * The Turnpike ― Inside the generator room of the overflow pipes.
 * The Drains ― Inside a converted railway carriage in the train station.
 * The Church ― Inside the church's vestibule, occupied by the Church Guy. It is unknown whether the Church Guy built this safe room or simply found it later.
 * The Town ― In the back room of a storage garage.

Dead Air

 * The Greenhouse ― Inside the kitchen of the Harbor View Hotel.
 * The Crane ― Inside one of the storage rooms in the self-storage facility.
 * The Construction Site ― Inside a hastily built structure made of wooden boards and metal bars at the entrance to the airport terminal. This is the only safe room in the game that is entirely constructed for this purpose, rather than an existing room that has been converted.
 * The Terminal ― Inside one of the airport's passenger jetways.

Blood Harvest

 * The Woods ― Inside one of the offices of the train depot.
 * The Tunnel ― Inside a maintenance locker room alongside the train tunnel.
 * The Bridge ― Inside a wooden shack at the top of the ridge next to the fallen bridge.
 * The Train Station ― Inside a converted railway carriage at the end of the railway bridge.

The Sacrifice

 * The Docks ― Inside one of the offices in the Brick factory.
 * The Barge ― A destroyed office room behind the grocery store near the Port.

Left 4 Dead 2
In Left 4 Dead 2, each level contains a safe room, with slight differences from the first game's safe rooms. Some safe rooms are larger than the first game's, such as an entire convenience store, as opposed to a single room.

Dead Center

 * The Hotel ― At the exit of the hotel lobby.
 * The Streets ― The Mall entrance by a parking lot that was being used by CEDA.
 * The Mall ― A back room in The Mall's maintenance corridors.

The Passing

 * The Riverbank ― An office room near the park.
 * The Underground ― A maintenance room on the other side of Rayford near the bridge.

Dark Carnival

 * The Highway ― A small shack off to the side of the park's main entrance.
 * The Fairgrounds ― The entrance to The Tunnel of Love.
 * The Coaster ― The entrance to the roller-coaster.
 * The Barns ― The entrance to the stadium where The Concert finale takes place.

Swamp Fever

 * Plank Country ― A large short pipe under a bridge.
 * The Swamp ― A small shack in The Shantytown.
 * The Shantytown ― A small shack near The Plantation.

Hard Rain

 * The Milltown ― A small building across the street from The Sugar Mill.
 * The Sugar Mill ― A gas station on the other side of the Sugarcane Field. Once the next level loads, the safe room door is switched from an entrance door to an exit door.
 * Mill Escape ― Same building as from The Milltown, but with the safe room doors reversed.
 * Return To Town ― A small, previously barricaded house with basic medical supplies.

The Parish

 * The Waterfront ― A small voodoo shop.
 * The Park ― A maintenance room under an overpass.
 * The Cemetery ― The back office of a store.
 * The Quarter ― A maintenance room at the base of The Bridge.