Oxygen tank

Oxygen tank
Weapon type	Other

The Oxygen tank is an explosive weapon found throughout the game, although it is less common than Gas Cans and Propane Tanks. Unlike the propane tank, which bursts instantly when struck by gunfire, the oxygen bottle will vent gas for a period of time before exploding. Thus, an oxygen tank is, in effect, a delayed-action time bomb. An exception exists in the case of a hit from a shotgun, in which instance the tank will explode instantaneously.

Oxygen bottles can be picked up with the Use key (default: E or"X" for Xbox 360). There is no inventory space for this weapon and so a player toting an oxygen tank cannot shoot but can still melee. 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. When shot, the escaping gas makes high pitched hissing noise that serves as a warning to clear the immediate area. Its slim profile, dull green colouration, low light conditions and the fact that it lies flat when dropped makes it a very difficult target to see and shoot beyond medium ranges: particularly when a Horde is helping to block the line of sight.

The oxygen tank is relatively common in The Hospital, The Train Station, the farmhouse of the finale in Blood Harvest, the Runway Finale and in ambulances throughout the game.

Tactics

• In some situations, the delay will be a problem, as the Special Infected will see you triggering the oxygen tank and can avoid the blast.
• Oxygen tanks are best used as defensive weapons deployed at choke points when preparing for a Horde or Crescendo Event.
• Like any explosives, oxygen tanks should not be dropped or fired close to team mates engaged in a fire fight. Any player close enough to hear the telltale whistle of escaping gas must quickly pull back to avoid being hurt in the impending blast.
• A precisely timed blast will blow a passing horde to bits.
• Oxygen tanks need a direct shot to be triggered. As noted above, they are sometimes difficult to see and shoot in the heat of action.
• When retreating from Infected or getting into the rescue vehicle, oxygen tanks set up ahead of time are great at stumbling the Tank or decimating a threatening horde at the critical moment.
• If a Witch is attacking a player, an extreme measure is to deploy and detonate an oxygen tank next to her. This will inflict a great deal of damage on her and she will be pushed back away from her victim. While the explosion will harm the victim, this will be less than that inflicted by the Witch's sustained attack.
• If an oxygen tank is unintentionally punctured and you hear the hissing sound, you can still pick it up and it will revert back to its normal, undamaged state.
• Throwing it by pressing the "fire" key while holding it in front of incoming Smoker's tongue will stop the threat.
• A hit from a shotgun will instantly trigger a blast.

Notes

• Of all the usable items in Left 4 Dead, the oxygen tank is the rarest.
• While it is assumed that the tank contains oxygen there is no in game proof that it does. The green bottle color is generally, but not exclusively, used to contain inert gases such as helium or neon. Medical oxygen bottles are usually either painted black or black with a white collar. However, there is no universal color code for gas bottles, and the color of any given gas bottle cannot be used as a definitive indication of its contents.
• No flammable gas spontaneously ignites or explodes on contact with the air. There is a wide variety of flammable gases (e.g. acetylene, methyl bromide,hydrogen, silane etc.) however they require the presence of oxygen or an oxidizing agent in the right concentration plus some form of primary ignition in order to "explode".
• Industrial and medical gas bottles are specifically designed to resist point-loaded impacts and it is unlikely that one would be reliably punctured by a pistol bullet, shotgun pellets or even a commercially loaded, small-calibre rifle projectile comprising a soft lead core and thin copper jacket. The self-same gas bottles also feature anti-explosion, fire-safety features such as a valve collar that melts and releases the bottle's contents or a 'blow out' aperture that operates when the internal gas pressure rises above a prescribed level. A gas bottle that lacks this type of safety feature (e.g. an early model scuba tank) is more likely to blow out its capping valve than it is to rupture explosively. On this basis, the actual contents and design of the in-game Oxygen Bottles remain conjectural.
• If you shoot the gas tank and then pick it back up it won't explode even if it's leaking gas.this applys when it is ignited as well