Isaac uses an Oxygen Recharge Station on the USG Ishimura.
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 of the other elements. Two atoms of the element binded to form dioxygen with the formula O2. Oxygen was the third most abundant element in the universe and the most abundant element by mass in Earth's crust.
There are several sections of the USG Ishimura, USM Valor and Titan Station that are open to the vacuum of space. When Isaac entered one of these places, his suit automatically sealed itself airtight and an Oxygen meter started to count down. If Isaac failed to either get to an Oxygen Recharge Station, a pressurized room or utilize an air can in time, he will suffocate and die.
Upgrading
The amount of oxygen that Isaac can use can only be upgraded by applying power nodes to the RIG's oxygen containment unit, raising it's 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.
Trivia
- 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)
- Instead of air cans, the player can find oxygen research points floating around the scatters of the S.C.A.F. fleet in orbit of Tau Volantis. They can be seen attached near airlocks, floating in space or they can be exposed by destroying hatches for presumably emergency oxygen research stations built around various ships' hulls which are far away from any nearby airlocks.
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