Propane tank

The Propane tank can be found throughout both Left 4 Dead and Left 4 Dead 2. An in-game propane tank is presented in the form of an everyday bottled propane gas canister most commonly associated with domestic heaters and barbecue grills. They show up very frequently in Survival Mode.

They can be picked up with the Use key (default: "E" for PC or "X" for Xbox 360) and will blow up with an explosion similar to that of a pipe bomb when shot. Like the oxygen tank, this weapon is commonly used during finales in order to set up traps - in this instance, selecting a weapon or pressing the Use key whilst carrying a Propane Tank causes the tank to simply drop and thus allows it to be placed fairly accurately.

A Propane Tank can also be thrown like a grenade (using the designated USE key) but the distance it travels is relatively short and it must still be set off with a gun shot. Nevertheless, a skilled player can use this ability to even the odds when, for example, a horde is in sight. Like Gas Cans, this weapon can be used to batter Infected with melee. Note that Propane Tanks will explode when enveloped in flame from a Molotov or a burning gas can.

The Propane Tank's blast radius seems to have been increased in the Crash Course DLC.

A Survivor too close to the center of explosion would be staggered for 1.5 seconds, similarly to the explosions of Oxygen tank, Pipe bomb and Boomer killed.

Tactics

 * The explosive power of the Propane Tank is useful for making a Tank stagger and lose his balance. This gives Survivors more time to move. Also, they are very useful when the Tank is on fire, and you want him to succumb to the flames. Propane tanks will stun the Tank for 3 seconds if he is close enough to the center of explosion. The damage dealt will be low, close to 20 even if the boss is in the center of explosion. Same applies to the explosions of oxygen tanks & pipe bombs. Boomers killed close to the Tank will apply the same stun as well, but will not damage him.
 * For a finale, try placing a group of propane tanks in a perimeter around the area you are guarding, this can be an extremely effective means of buying time when you need to heal or grab ammo.
 * Try placing these near the areas where the rescue vehicle shows up during finales, as it can clear the area before you reach the vehicle, giving you a better chance of reaching it on higher difficulties.
 * When shooting the Propane Tank, try to keep your distance because of its large explosion radius.
 * If used as a trap, try to give yourself a clear shot at it. Make sure that you don't have to jump out of a good cover spot to shoot it or else you may get overwhelmed by the Infected and your friends might not be able to save you.
 * When a horde is moving around a propane tank, be sure to time the shooting on the tank so that it is surrounded by the horde. Doing this will make a more efficient use of the Propane Tank. This can make shooting the Propane Tank harder with weaker weapons however, as the horde will block your shots.
 * On the last two chapters of the No Mercy campaign, the propane tank can be used to make a Tank fall off the edge. Propane tanks usually spawn in the unfinished part of the hospital, and sometimes the finale. When a Tank comes near an edge, the propane tank (if placed properly) can knock him off to his death. This tactic is useful on campaigns, especially when playing on Expert, and also Versus, when a Tank rushes.
 * If a Witch is attacking a player, and someone throws a propane tank near her and shoots it, the Witch will lose a great amount of health, get stunned for a few seconds and be pushed back a couple feet. Additionally, the explosion hurts less than her clawing so this will spare that player a few health points and delay the Witch's attack.
 * If you place a lot of them near a Witch and set it off, the Witch can, rarely, remain undisturbed. It happens more frequently when the Witch hits a tree, a car, or when she falls off something.
 * The Propane Tank, like the gas can and the oxygen tank, can be thrown with the "fire" button while holding it.
 * An extremely useful tactic in Left 4 Dead 2 is to get a bile bomb and a propane tank (if possible) and put the propane tank down, then throw a bile bomb somewhere close to it. Then shoot the propane tank. This will eliminate all surrounding infected and will draw any nearby zombies to it. This is extremely useful on expert, but try to shoot the propane tank with a Magnum or a Hunting Rifle to prevent the zombies from blocking it. This is not effective on Left 4 Dead as the only horde drawing player item is a pipe bomb, which explodes by itself.
 * Clustering several propane tanks together can create a massive explosion with a large radius. This can do some support damage to a Tank (~20 per explosive item) but can also cause massive damage to yourself or teammates if they are too close to the blast.
 * The Grenade Launcher can add to the explosive properties of the propane tank with its own explosion, increasing its potency.
 * The Propane Tank can be used to negate fall damage with its explosive knockback. If you jump from a height while holding a propane tank, drop it below yourself as you fall, and immediately shoot it, the propane tank will explode below you and interrupt your fall, decreasing your velocity and, therefore, the fall damage you receive.
 * Note that you will take damage from the propane tank itself, though this will typically be much less than potential fall damage.