Aircraft carriers like USS Harry S. Truman (CVN 75) rely on underway replenishments of food and resources to stay out to sea for long periods of time, but some resources can be made out of thin air.

Truman's engineering department works night and day to make pure oxygen and nitrogen (O2N2) for use by both pilots on the flight deck and Sailors around the ship.

"Starting up the plant and making a good product is not a fast process," said Machinist's Mate 1st Class David Combs, the divisional leading petty officer for engineering auxiliaries division. "You can't rush it. If you do, that's when mistakes happen and people get hurt."

Engineering coordinates with Carrier Air Wing (CVW) 1 to ensure that they produce enough oxygen and nitrogen to meet demands, which can vary based on the aircraft. Oxygen will always be used for Aviator Breathing Oxygen (ABO), however nitrogen serves multiple purposes around the ship.

"Our ship cannot fly planes without having the liquid oxygen and liquid nitrogen that we make," added Combs. To get its supply of O2N2, Truman uses a very tedious process to liquefy and separate gases.

O2N2 is made by taking atmospheric air (78% nitrogen, 21% oxygen, 1% other) and compressing it with a low-air compressor. After it is compressed to 106 psi, it is sent to the producer/generator where the processed air is cooled below negative 200 degrees Fahrenheit. At that point, the air becomes liquefied and nitrogen is distilled from the liquid air. The result is both pure liquid nitrogen and pure liquid oxygen. The cryogenic liquid is then sent to designated storage tanks, which are able to hold 1,500 gallons of each. Once stored, it is turned into high pressure oxygen and nitrogen gases for ship-wide use.

"The whole process can take up to two weeks," said Machinist's Mate 1st Class Bobby Njoo. "We can make up to 25 gallons per hour of liquid nitrogen and up to 15 gallons per hour of oxygen."

Liquid nitrogen processes easily, but liquid oxygen produces methane. When those methane levels become too high, the oxygen will no longer be considered safe for use as ABO. When methane is present, it asphyxiates the oxygen and ends up causing anyone who breathes it to experience a lack of oxygen, or hypoxia.

"Typical symptoms experienced with hypoxia include loss of color vision, loss of vision, 'air hunger' (fast breathing), tachycardia (rapid heart rate), dizziness and lightheadedness, anxiety, chest pressure, numbness and/or tingling in the hands, feet, and/or mouth, and decreased concentration," said Lt. Natalie Slepski, Flight Surgeon for CVW-1.

Along with aviation uses, oxygen produced is also used by Truman's medical team.

"Without the O2N2 plant, [the ship's] medical needs would be greatly undermined," said Hospital Corpsman 3rd Class Deven Sheldrew. "[Medical] also uses the O2N2 plant for filling the oxygen tanks when they become low, and having this accessibility means that every patient that needs oxygen can receive it."

Prior to issuing any oxygen, engineering Sailors sample it to make sure that it is pure enough to use without suffering from any potential effects.

"Working in the O2N2 plants carries inherent risk that requires cryogenics technicians to be focused, mature and responsible," said Chief Machinist's Mate Kelly Barncord, the cryogenics chief onboard. "The cryogenics technicians in O2N2 work very hard, every day to ensure we maintain a safe environment."

Truman is deployed in the U.S. Sixth Fleet area of responsibility as part of an ongoing rotation of U.S. forces supporting maritime security operations in international waters around the globe.

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