The Hospital

The Hospital is the fourth chapter of the first campaign, No Mercy. It takes place in the city of Fairfield, inside of the overwhelmed Mercy Hospital. The goal of the Survivors here is to get to the roof, where they will be able to make contact with the helicopter which has been flying around the city, while fighting hordes of Infected doctors, patients, and other people. The video walkthrough is on the no mercy campaign page here's the link for it http://left4dead.wikia.com/wiki/No_Mercy

Campaign
At the beginning, the AI Survivors will grab:
 * Bill will grab an assault rifle.
 * Francis will grab an auto shotgun.
 * Louis will grab an assault rifle.
 * Zoey will grab a hunting rifle.

Otherwise, they will keep the weapons they had in the last chapter (see The Sewer for a list of weapons they will grab there).

It's been a long run. Through apartments, abandoned subways, and sewers you've gone. But you're here now. Rescue awaits you on the roof of the hospital. Now, all you have to do is get everyone there alive, and you'll have made it. Take a breather, if you must, and be prepared to run through the forsaken halls of Mercy Hospital.

Of course, you start this level out in a safe room. There are tier 2 weapons sitting on the table, as well as an extra pistol and a box first aid kits on the wall. Stock up and get ready to move. Due to the closed quarters of this level, an auto shotgun is recommended. Take whatever you'd like, open that door, and head out.

Head to the right of the door, down the hall, and head for the light at the end which leads to some stairs. You can go to the left, though, and look for supplies, or turn at the bend into a darkened hallway, as well. However, both are ultimately dead ends. Go up the flight of stairs and onto the next floor. Take a look around, if you must, but the way to keep going is to the left; either by the immediate route, or a small detour through a few rooms.
 *  This is one of the most likely times for a Tank or Witch to appear (especially in versus mode). If you hear either of them, get ready to either fight or try to file around the Witch (if there is one), although they usually spawn directly in the way. 

Head for the stairs on the far side of the room, possibly pausing to look inside of the few rooms along the way if you really want supplies, and go down the hall until you reach more stairs. Go up, and keep moving.
 *  This is another very likely spot for a Tank or Witch to appear. From this point to the elevator, watch out! 

Take a look behind the desk here. There tend to be some supplies around this area, if the Director is forgiving. Move down a rather long hallway, lined with beds and gurneys, and you'll find yourself at an elevator. Don't you just hate waiting for the elevator when you've somewhere to be? Don't hit the button yet, though! There's a pile of ammo sitting on a bed blocking off a corner (which is a very common tactic to use for this section, though it's mostly when there are other players), and sometimes supplies are hiding off in one of the adjacent rooms down this hall. Take a look around and make use of what you can, and only when you and everyone else is ready, hit the button and get ready to wait. Oh, and there's a horde coming.

They'll be coming in from almost every direction—even dropping down from a vent over your head, breaking down walls all around you. At this point, though, there are a few different tactics which can be used to great effect:
 * Pipe bombs, obviously. Throw as many as you've got, and it easily thins out the horde.
 * Molotovs. Throw them down at one of the pathways the Infected will be charging in from, and it does most of the work for you.
 * There is a small closet on the other side of the wall where the elevator and bed are. Everyone can go in there, but be careful of Special Infected that drop out of the ceiling!
 * As aforementioned, everyone can get in the corner behind the bed. Not only does the bed keep anybody from being dragged away by a Smoker, but the wall also covers your backs quite well.

In general, just stay together, preferably close to the elevator, and you should be fine. Once the elevator finally gets to your floor, hurry and get on before more come running.

As the elevator slowly goes up, this would be a nice time to work out who needs health. Figure it out, but be ready to hit the ground running when it reaches its destination—the 28th floor.
 *  This is the final place a Tank or Witch generally spawn, usually farther down and not far from the safe room. Needless to say, with all of the holes in the walls, the Tank is definitely the more dangerous of the two here. Just avoid the open points in the walls and shoot as much as you can. 

You're almost there. The elevator lets you out to an unfinished part of the hospital, which is quite obviously still under heavy construction, judging by the wooden beams everywhere... as well as the lack of outer walls. You're almost to the safe house, though! Run through the area (carefully, you don't want to fall off the roof!), and you'll have made it. Be careful, if a Tank spawns here he can send you flying off the roof. Get everyone inside, and shut the door when they are. Congratulations, you've made it through The Hospital! Take a moment to catch your breath, and get ready for the Rooftop Finale.

Survivors
Now that humans are controlling the Special Infected, things can only get harder. However, they can't spawn until you leave the safe room. That doesn't mean that you should let them have a good chance to find just the right spot, though! Hurry up and get your supplies, and get running!

Just outside of the safe room is a treacherous corridor where Infected can quickly overwhelm the survivors. There are many rooms and a side passage on this long hallway. These serve as easy ambush points for each of the Infected. Watch out and move swiftly, but stay vigilant!

Remember that throughout the level, you need to stick together. Especially now player-controlled enemies have joined the fray. When entering and exiting the stairs, be cautious of Hunters waiting to pounce and Boomers waiting to vomit - these areas are their favourite.

A competent team of survivors should not encounter any problems until they reach the Crescendo Event at the elevator. Here, you need to find an extremely secure location and buckle down for a hard fight. Your enemies won't be merciful in any way, so return the favour, and show no mercy!

It is important to be ready for anything when the lift reaches the top and opens out onto the construction area. Here anything can happen, from Boomers lying in wait to a Tank around the bend. Whatever happens here, be ready for it.

This is a point that cannot be stressed enough. When you see the safe room, do not make a dash for it alone. If you do, you may end up getting yourself killed. Stick with your teammates, move as they do. Cover them and they'll cover you.

Infected
Boomers: Close quarters. Your favourite two words together. Here, you are the infected's main chance of success. You are their main weapon. Cover the survivors in your putrid-green bile and and make sure they can't see what they're doing. Once you've covered them, check for other special infected. If none are around, don't be afraid to get in there and use your melee attack on the survivors. Remember all of those places where you simply couldn't avoid the Boomer's bile? Use them! Take advantage of your knowledge as a survivor.

Hunters: Close quarters. Not your forte, but not enough of a hindrance to make you ineffective. You can still lurk in dark rooms and strike at the last passing survivor. Try to outsmart your targets, and hide in effective yet unusual positions. Also, considering that height is not available for you to get instant damage pounces, don't underestimate your secondary attack. Your melee is very strong and can quickly incapacitate a heavily wounded survivor. Also note that when joining in with a horde of common infected to slash at your target, you are less likely to be noticed and killed than your fellow special infected.

Smokers: Close quarters. They are certainly not made for you. You are made for long distances and heights. Don't let this discourage you, though. Use the long corridors to your advantage. The survivors do well indoors, but with a well aimed Smoker's tongue, you can outdo them. Work together with the other special infected and show them that Smokers are deadly to them no matter where they go.

Tanks: This is a beautiful hospital. Bloody, stuffed with infected, and dangerous to survivors. Perfect. As with most interiors you are a force to be reckoned with. You can be the very difference between victory and defeat. These tight corridors and compact rooms are absolutely ideal for you. As long as your enemies are not a team of perfect players, you should be able to do a large amount of damage to those immune annoyances. Lead your fellow infected, and crush the survivors once and for all!

Survival
Open Room Method


 * The doors in the hospital are easily broken by infected attacks and are nearly invulnerable to your attacks. The keyword is nearly, you can destroy the doors by unloading a ridiculous amount of shotgun blasts into them and using your melee a few times. The doors will eventually fall and break. This is required to use this method. Facing away from the lift, turn down the corridor on your right. At the very end of this corridor is a set of double doors. If your team breaks into this room, it can be used to hold out for a long time. This room contains a pipe bomb, a molotov, pills, and oddly an extra pistol.


 * This method limits the infected entry points to only through the doorway itself. Smokers, Hunters and Boomers can all easily be dealt with from here if your team is ready to cover you. Even when the Tank arrives, he can easily be beaten, as not only does he often spawn far down at the end of the corridor, but there are a lot of static gurneys for you to clamber over whilst battling the Tank inside the room. If the Tank does manage to do damage, all is certainly not lost. This room is very close to the ammunition, weapons and first aid kits. From here, a competent and cooperative team can achieve around fifteen minutes.

Trivia

 * This level is often considered one of the most liked levels in Left 4 Dead. Also one of the scariest, since patient and doctor zombies tend to appear from dark and silent rooms, and hospitals are always the scariest places in zombie themed movies/games.
 * At the start, if you go in some rooms, a zombie can be heard talking to a wall.
 * In several of the examining rooms, there is an x-ray of a hand with four fingers, which is a reference to the cover of the game.
 * In the chapter's starting safe room, there is some Graffiti on the wall, one area of which will say that "I killed..." some number of zombies, the last number of which 53,595. This is the exact number of zombies that the player needs to kill get the Zombie Genocidest achievement. This achievement in itself is a reference to the Zombie Genocide achievement from the popular zombie hack and slash video game Dead Rising, and that game's setting of the town of Willamette, Colorado, where the population is 53,594.
 * As you start the game, run up the stairs and into the large main room on that floor, to the right of the large door you most likely entered by, there is a door handle on the wall (more than likely an oversight).
 * An effective yet 'cheap' as it's considered by most players strategy; While you are on the infected team in versus, make sure your team is all hunters.(Note: This takes quite an amount of teamwork) Make your way to the elevator shaft before the Survivor team does, and tell all 4 of your team members to get in the elevator before they press the button to call the elevator to get them. Once they do, get your team to prepare themselves and as soon as the door of the elevator opens, the survivors will probably not be aware of your presence and will try to walk in as if your team is not there. Before they have a chance to do so, your team should each pounce on one survivor, this will kill all four of them quickly and easily.
 * The Hospital level may be a reference or homage to the 2002 film 28 Days Later where the main character wakes up from a coma to find the hospital completely deserted.

All of the following bugs have been fixed on both the PC and Xbox 360 version:


 * After the battle with the horde at the elevator, if a Survivor managed to become incapacitated inside the elevator for any reason and was revived once the elevator had been activated, the elevator rose but they did not. They would also have been unable to leave the elevator shaft, and have been easy prey to any other Infected.
 * Throwing a propane tank or oxygen tank at a Survivor in the lift would incapacitate them and cause them to fall through the floor of the lift, leaving them at the bottom of the elevator shaft.
 * In Versus mode, any of the Special Infected (except the Tank) were able to run ahead in the level to the top of the elevator shaft and repeatedly melee the trailer in front of the elevator, eventually pushing it in front of the doors and trapping the Survivors when they reached the top. The Tank can still hit the trailer and move it in front of the elevator, but objects hit by the Tank eventually disappear, making this a temporary obstruction.