section_path: Safety concerns/Equipment hazards/Artificial atmosphere
section_name: Artificial atmosphere
paragraph_text: Artificial atmosphere
  
  There are two basic choices for an artificial atmosphere: either an Earth-like mixture of oxygen and an inert gas such as nitrogen or helium, or pure oxygen, which can be used at lower than standard atmospheric pressure. A nitrogen–oxygen mixture is used in the International Space Station and Soyuz spacecraft, while low-pressure pure oxygen is commonly used in space suits for extravehicular activity.
  
  The use of a gas mixture carries the risk of decompression sickness (commonly known as "the bends") when transitioning to or from the pure oxygen space suit environment. There have been instances of injury and fatalities caused by suffocation in the presence of too much nitrogen and not enough oxygen.
  
  A pure oxygen atmosphere carries the risk of fire. The original design of the Apollo spacecraft used pure oxygen at greater than atmospheric pressure prior to launch. An electrical fire started in the cabin of Apollo 1 during a ground test at Cape Kennedy Air Force Station Launch Complex 34 on 27 January 1967, and spread rapidly. The high pressure, increased by the fire, prevented removal of the plug door hatch cover in time to rescue the crew. All three astronauts— Gus Grissom, Ed White, and Roger Chaffee —were killed. This led NASA to use a nitrogen–oxygen atmosphere before launch, and low-pressure pure oxygen only in space.