Oxygen tank

The Oxygen tank can be found throughout the game and works similarly to the propane tank. However, instead of exploding instantly like the propane tank, they will vent gas for a period of time before exploding. In effect, they are a large time bomb. They can be picked up with the Use key (default: E or"X" for Xbox 360) and the player cannot shoot while holding an oxygen tank, but can still melee. There is no inventory space for this weapon, so the only method of transporting it is to pick it up and carry it. Like the other thrown items this weapon is usually found during Crescendo Events and the finale, but it can be found around some parts of the middle maps. The oxygen tank does not have as much power as a propane tank, but players should take caution, since it can be ignited while a player is holding it. When shot, it spurts flame from the hole made before exploding.

The oxygen tank can be found easily in The Hospital. Oxygen tanks can also be found in ambulances (there is one located in front of the emergency room).

You may also find about 3 in the farmhouse of the finale in Blood Harvest. Most are upstairs in the bedrooms.

Occasionally, one or more oxygen tanks may spawn in the back of the truck (the one with the wood panels) near the escape plane during the Runway Finale.

Tactics

 * In some situations, the delay will be a problem, as Special Infected will see you triggering the oxygen tank and can avoid the blast.
 * Be wary during firefights, as the oxygen tank will make a hissing noise before exploding. If you happen to hear this when you know someone hadn't intended on shooting the tank, try to locate the oxygen tank and distance yourself from it.
 * A precisely timed blast will blow a passing horde to bits. Propane cans need a direct shot to be triggered and a passing horde may block the tank until a majority of them pass.
 * When retreating from Infected or getting to the rescue vehicle, oxygen tanks set up ahead of time are great in slowing down the Tank and/or destroying the horde.
 * If a Witch is attacking a player, and someone throws an oxygen tank near her and shoots it, the Witch will lose a great deal of health, and she will 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.
 * The oxygen tank can delay the Tank and let you make an escape during the run to the rescue vehicle, as it navigates around it to avoid damage, giving you a few extra seconds of precious time.
 * If an oxygen tank is unintentionally punctured and you hear the hissing sound, you can pick it up and it will revert back to its normal, undamaged state. On the other side, this can be unfortunate because otherwise you could trigger it by shooting it and then pick it up and toss it like a grenade.
 * Throwing it, by pressing the "fire" key while holding it, in front of incoming Smoker's tongue will stop it.
 * Of all the usable items in Left 4 Dead, the oxygen tank is the rarest.
 * Also a Hit by a shotgun will instantly trigger a blast.