Oxygen (O₂) is used across medicine, manufacturing, aerospace, and chemical production, making it one of the most widely consumed industrial and medical gases in the world. In hospitals, it keeps critically ill patients alive. In steel mills, it burns impurities out of molten iron. In rocket engines, it makes combustion possible where no atmosphere exists. Here’s how O₂ is used in each of these areas and why it matters.
Medical Oxygen Therapy
The most familiar use of O₂ is supplemental oxygen for patients who can’t maintain healthy blood oxygen levels on their own. For most acutely ill adults, clinicians aim to keep oxygen saturation between 94% and 98%. People with chronic lung conditions like COPD are managed differently, with a lower target of 88–92%, because giving them too much oxygen can actually suppress their breathing drive.
Oxygen is delivered in several ways depending on severity. A simple nasal cannula provides low-flow oxygen for mild cases, while face masks and high-flow systems handle more serious drops in saturation. The key principle in modern guidelines is controlled delivery rather than giving oxygen liberally. Maintaining a specific saturation target matters more than simply flooding the lungs with extra O₂.
Beyond standard therapy, oxygen is used at elevated pressures in hyperbaric chambers. Patients breathe pure oxygen inside a pressurized room, which forces far more O₂ into their blood and tissues than normal breathing allows. This treatment is a standard of care for decompression sickness (the “bends” in divers), carbon monoxide poisoning, diabetic wounds that won’t heal, radiation injuries, and severe soft-tissue infections like gas gangrene. The high oxygen concentration accelerates healing in damaged tissue and helps the body fight certain infections that thrive in low-oxygen environments.
Steel Production
Steelmaking is one of the largest industrial consumers of pure oxygen. In the basic oxygen steelmaking process, pure O₂ is blown at supersonic speeds through a water-cooled lance into a vessel of molten iron. The oxygen reacts with impurities dissolved in the iron, primarily carbon, silicon, manganese, phosphorus, and sulfur, and either traps them in a layer of liquid slag floating on top or drives them off as gas.
Carbon removal is the most critical step. Oxygen reacts with iron to form iron oxide, which then reacts with dissolved carbon to produce carbon monoxide gas that escapes the melt. This is what transforms brittle, high-carbon pig iron into usable steel. The entire process takes roughly 20 minutes per batch, and it replaced older, slower methods that relied on blowing air (which is only about 21% oxygen) through the molten metal. Using pure O₂ made steel production dramatically faster and more efficient.
Rocket Propulsion
Rockets can’t rely on atmospheric oxygen because most of their flight takes place in the vacuum of space. Instead, they carry their own oxidizer, and liquid oxygen (often abbreviated LOX) is the most common choice. O₂ doesn’t burn on its own. It enables burning by reacting with a fuel, releasing the enormous energy needed to generate thrust.
The simplest pairing is liquid hydrogen and liquid oxygen, which produces only water vapor as exhaust. Many launch vehicles instead pair LOX with a refined kerosene fuel, which is denser and easier to store. In either case, the liquid oxygen is chilled to around minus 183°C to keep it in liquid form, then pumped into the combustion chamber where it mixes with fuel and ignites. A typical rocket carries far more oxidizer by mass than fuel, because combustion reactions consume large quantities of oxygen.
Chemical Manufacturing
High-purity oxygen is a critical ingredient in producing many industrial chemicals. One major example is ethylene oxide, a compound used to make antifreeze, plastics, detergents, and sterilization agents for medical equipment. In this process, ethylene reacts with O₂ over a catalyst to form ethylene oxide. Plants can use either compressed air or pure oxygen (99% purity) as the oxygen source, but pure O₂ improves the yield and reduces unwanted byproducts like carbon dioxide and water.
Oxygen also plays a role in wastewater treatment, where it’s dissolved into water to support the microorganisms that break down organic waste. In metalworking beyond steelmaking, oxy-fuel torches combine oxygen with acetylene or propane to cut and weld metals at temperatures exceeding 3,000°C. Glass manufacturing, paper bleaching, and fish farming all rely on supplemental O₂ as well.
Atmospheric Protection
High in the stratosphere, O₂ molecules are constantly being split apart by solar radiation and reassembling into ozone (O₃). This ozone layer absorbs the most damaging wavelengths of ultraviolet radiation before they reach Earth’s surface. UVC radiation is completely absorbed by ozone and normal oxygen, while most UVB is filtered out by ozone alone. Without this cycle of oxygen forming and reforming, life on land would face levels of UV exposure that cause rapid DNA damage in skin, eyes, and plant tissue.
Risks of Too Much Oxygen
Oxygen is essential, but it becomes toxic at high concentrations or pressures. Breathing gas mixtures with an oxygen partial pressure above normal atmospheric levels for extended periods can damage the lungs, causing inflammation and fluid buildup. At even higher pressures, such as those encountered during deep diving or hyperbaric treatment, the central nervous system is at risk. The hallmark sign of this toxicity is seizures, which can be followed by fluid accumulation in the lungs.
This is why medical oxygen is carefully titrated to a target range rather than given freely, and why divers using enriched oxygen mixtures must calculate strict depth and time limits. Pure oxygen also creates a serious fire hazard. It doesn’t burn by itself, but it makes everything around it ignite more easily and burn more intensely. Materials that are barely flammable in normal air can combust violently in an oxygen-enriched environment, which is why smoking near oxygen equipment and using oil-based products around oxygen fittings are strictly prohibited.