Pipe Bomb

"This shit looks real jury-rigged."

- Louis

"Chase this, you zombie bastards!"

- Nick

The Pipe Bomb is an IED that can be used offensively, defensively and for diversionary purposes.

The visual design is stereotypical but with the addition of a bright red LED and loudly beeping smoke detector to attract Common Infected when armed and thrown. Pipe Bombs explode five to seven seconds after being deployed.

Its blast radius is relatively small, being confined to little over three to four meters (10 to 13 feet) on the normal difficulty setting; however, since a well-deployed Pipe Bomb is usually tightly surrounded by enemies, as many as 20 or more can be killed at once. Since a Pipe Bomb blast can injure a Survivor, care is needed to ensure that teammates are at a safe distance when one goes off.

Pipe Bombs can be an extremely useful weapon in many situations. The Pipe Bomb can be used offensively to clear out an area, defensively against a Horde or to draw off enemies from an incapacitated teammate, and for diversionary purposes such as when disengaging at the end of a finale.

Tactics

 * This weapon is perfect for quickly clearing out an open area filled with loosely gathered Common Infected, saving ammo and time.
 * Apart from the Bile Bomb, the Pipe Bomb is the ideal diversionary device to deploy against the Horde during the final moments of a finale when sprinting for a rescue vehicle.
 * Deploy a Pipe Bomb to draw enemies away from a teammate who is either incapacitated or covered in Boomer bile. Infected AI places higher priority on the Pipe Bomb over Survivors covered in bile, but Commons may still attack if already engaged.
 * If the Common Infected are too close to you or your allies, they may ignore the Pipe Bomb and attack. Push them away to disengage them so they will chase after the Pipe Bomb.
 * Keep Pipe Bombs in reserve for dealing with large Hordes. Remember: this weapon's lethality is directly proportional to the number of enemies it can attract.
 * Do not throw multiple Pipe Bombs. Common Infected will run towards the first one thrown and ignore the others.
 * Let your teammates know when you are going to throw a Pipe Bomb to prevent them from wasting theirs.
 * Do not throw a Pipe Bomb when a large number of enemies are climbing a fence, barrier or wall. They are programmed to complete their climb before turning and running towards the bomb, by which time the bomb may have exploded harmlessly. Enemies only respond if they are standing on the ground.
 * Common Infected who are not killed outright by the explosion are stunned and thus vulnerable to a follow-up attack.
 * The kill radius may vary with the difficulty level.
 * Special Infected and Uncommon Worker Infected are not attracted to Pipe Bombs.
 * Witches and Tanks can be stumbled or stunned if a Pipe Bomb explodes near them, but won't chase them.
 * This can be used to stumble a Tank off a cliff, instantly killing them, or buy time when killing a Witch.
 * Be mindful of your throws; a poorly planned Pipe Bomb is capable of startling a witch or activating a car alarm.
 * Pipe Bombs are less effective in Left 4 Dead 2 since passive enemies appear to respond more slowly to their beeping and smoking, as well as the lighting, and sometimes not at all.
 * In Left 4 Dead 2, when a Pipe Bomb is thrown down a building or bridge, the Infected will still follow the Pipe Bomb and plunge to their deaths.
 * This can be used during the start of "Dead Center" or the finale of "The Parish". In "Dead Center", you can get a potential double-kill with it; by throwing the bomb from the lower floor and through the sky window of the lobby, you can cause the Infected on the current floor and those in the lobby to be killed by it; the ones on the current floor will follow the bomb, while it will destroy the ones in the lobby.
 * When a Special Infected is around a corner or behind cover and cannot be shot, a Pipe Bomb can be tossed or bounced around the angle to draw them out, injure or stun them.
 * If you decide you don't want to use your Pipe Bomb (or are about to use it accidentally), switching weapons cancels the throw.
 * While more difficult than using Molotovs, it is possible to free teammates who are pinned by Special Infected and out of your line of site with a Pipe Bomb. If, for instance, three Survivors have crossed a point of no return (i.e. jumped down a hole in the floor, such as in "The Coaster") and the fourth was dragged away from their line of sight by a Smoker, a well thrown Pipe Bomb could be used to kill or stumble the Smoker, saving the Survivor.
 * A lone Survivor can employ a similar strategy if they believe they will be pinned by an Infected. Throwing a Pipe Bomb nearby will knock any Special Infected off the Survivor once it explodes, though the timing and positioning of the bomb must must be precise to be effective.
 * Be careful not to stand too close to a Pipe Bomb when it explodes. At most ranges, it will deal relatively little damage to you, but if you are very close to it, the Pipe Bomb can cause significant damage and stumble you.
 * If you are very close to a Pipe Bomb and don't have time to get out of the blast radius, a carefully timed jump will cancel your stumble animation.
 * 'Stumbling' in mid-air cancels all downward momentum, so jumping on a pipe bomb from a height with proper timing can be used to jump down from a great height without dying. This is very difficult, however, because the timing must be exactly right: too soon and you are outside the stumble radius and fall to your death, too late and you have already hit the ground and died when the Pipe Bomb explodes.
 * Throw Pipe Bombs low to the ground, if possible. If a Pipe Bomb is thrown too high, Common Infected will stand still until the Pipe Bomb reaches a height low enough that they can locate it. This decreases the number of Common Infected that will reach the Pipe Bomb before it goes off, thereby decreasing its effectiveness.
 * Similarly, unless the Pipe Bomb is only meant to distract the Infected, do not throw it very far out of bounds. It is possible for the Pipe Bomb to land somewhere that the Common Infected cannot reach or get to, causing them to stand still until it goes off.

Behind the Scenes
According to the game's Developer Commentary, the Pipe Bomb did not have the flashing light when it was originally conceived; instead, it served as a conventional grenade. There were some issues with this, however: rushing Infected would ignore the grenade, and often run past it, making the Pipe Bomb useless unless perfectly timed. A worse problem was when the grenade would bounce off the Infected and back toward the thrower. Valve fixed the problem by making the Pipe Bomb attract Common Infected, and added the oxygen tank to perform the role of the earlier Pipe Bomb.

The Pipe Bomb is based on Counter-Strike HE Grenade. Its "price" in the Pipe Bomb's weapon file is the same as the HE Grenade's and the Pipe Bomb's sounds are in a folder called "hegrenade".

It is likely that the Pipe Bomb was a regular grenade at one time. Hidden in the game's files is a very early grenade icon for the HUD; this grenade looks exactly like the Counter-Strike: Source HE Grenade.

One of the proposed uses of the Pipe Bomb was for it to be an anti-Tank weapon. This ability is discussed in the Developer Commentary and can be seen in this video dated August 27th, 2008. While the video doesn't show the Pipe Bomb killing the Tank, it portrays it as useful against one.