From Halopedia, the Halo wiki
A cryo-chamber, often called a cryotube, is plastasteel pod with a form-fitting gel bed that allows all of a starship's non-essential personnel to be cryonically frozen for long periods of time, most commonly during prolonged slipspace jumps. An example of this is John-117, who was stored in a cryo-chamber aboard the ship UNSC Pillar of Autumn and later unhatched from the cryosleep chamber by Tech Chief Thom Shephard along with Tech Officer Sam Marcus.
Known models of the cryo-chamber include the Mark VII Personal Suspension Unit, manufactured by Jakubaitis Standard Systems. It was widely disliked by UNSC personnel because of its inferior moisture balancing; this resulted in dry, itchy skin for a day or more after awakening, known as "cryo-itch". It was later replaced by the Mark VIII Cryogenic Suspension Chamber, although many older craft still use the Mark VII.
Cryo chambers are referred to as "the freezer" in slang. Another slang term for the chamber is "the Admiral's wife" because it is a "frosty bed". Being put in cryo is also referred to as being "put on ice."
The cryo-chambers are usually stored in a dedicated area of the ship, commonly referred to as a "cryo bay". Cryo chambers are monitored by the ship's AI, and the AI can awaken crew members at a moment's notice. Cryo-computer is designed to change the pharmaceuticals dosage if an individual appears as though they might wake from cryogenic sleep. Cryo wake-up protocols demand that crew check each other to make sure everyone revives from cryo all right. There is usually a medical pod in cryogenics bays for emergency resuscitation situations.
To prevent ice crystals from forming in one's cells, a person going into cryosleep must be injected with a chemical known as cytoprethaline. A substance known as bronchial surfactant must also be ingested to protect the lungs. Individuals in cryo tubes are given a steady supply of pharmaceuticals that control the frequency and duration of cryosleep cycles along with influencing the content of their dreams. While in cryo, humans do not age; as a result many UNSC military personnel, who routinely undergo long stretches of cryosleep during slipspace travel, effectively age slower than most civilians.
Extended periods in cryosleep can result in a condition often called freezer burn which is a pain caused by cryo pharmaceuticals trapped in muscles and joints. People are almost always stored in cryotubes naked, as covered skin generally reacts badly to the cryo process, leaving skin raw and blistered. However, it is possible for Spartans to go into cryo chambers fully armored, using their conditioning and training to ignore the pain. Cadets at Corbulo Academy regularly wore carbon-black skintight clothing during cryo training; the use of these "cryo suits" did not lead to the blistering frequently caused by normal clothing. As of the year 2557, UNSC personnel on at least some ships are given special white jumpsuits to wear when going into cryo.
Entering cryo can also be used as an emergency measure. Often a person may be placed in cryo in order to save them from succumbing to grievous injuries, such as in the case of Linda-058, who was placed in a cryo-chamber after being severely injured during the Fall of Reach, and successfully revived later despite being previously declared clinically dead. Each chamber will hold an individual for as long as necessary, and can be ejected prior to an emergency landing, thus saving some crew from harm to be recovered later. Some pods feature slow-impulse thrusters for limited maneuvering in the event of ejection. After the aft section of the UNSC Forward Unto Dawn was left drifting in space years from rescue, the Master Chief entered cryo sleep in order to survive the wait for rescue. When the UNSC Spirit of Fire was left adrift in space without a slipspace drive, its crew entered cryosleep for 28 years, only to be awakened when the ship unexpectedly arrived at Installation 00.
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