Oxygen is a member of the chalcogen group on the periodic table, and is a highly reactive nonmetallic period 2 element that readily forms compounds with almost all other elements. Two atoms of the element bind to form dioxygen, with the formula O2. Oxygen is the third most abundant element in the universe and the most abundant element by mass in the Earth's crust.
There are several sections of the USG Ishimura, USM Valor, and Titan Station that are open (or have become open) to the vacuum of space. When Isaac enters one of these places, his suit automatically seals itself airtight, and an Oxygen meter starts to count down. If Isaac fails to either get to an Oxygen Recharge Station, a pressurized room or utilize an air can in time, he will suffocate and die.
The amount of oxygen Isaac can use can only be upgraded by applying power nodes to the RIG's oxygen containment unit, raising its capacity. Isaac can carry a maximum of two minutes and ten seconds of air in Dead Space, three minutes of air in Dead Space 2, and seven minutes of air in Dead Space 3.
- Necromorphs do not appear to respire aerobically, and are thus unimpeded by depressurized or otherwise unbreathable atmospheres.
- A mistake in the original Dead Space was that the it was said the Flamethrower needed oxygen in order to operate (despite using a typically oxygenized hydrazine fuel). However, this mistake is corrected in Extraction and Dead Space 2.
- Air Cans do not return in Dead Space 2. All vacuum areas of the game have Oxygen Recharge Stations and Isaac starts with more Oxygen for his non-upgraded suit than in Dead Space.
- Although a fully upgraded air counter reads 180 seconds, in practice it actually lasts 205 seconds in real time. (Dead Space 2)