WARNING: Liquid oxygen is extremely dangerous. Contact your Division Safety Coordinator for help planning your work before ordering liquid oxygen.
Although oxygen is not flammable, it is a strong oxidizer and can cause flammable and combustible materials to catch fire and burn. Liquid oxygen is not only 100% oxygen by volume (compared to 20.9% in air), but that oxygen is far more concentrated as a liquid than as a gas, since liquid oxygen expands by 860 times when allowed to warm to room temperature. One milliliter of liquid oxygen has as many oxygen molecules, and thus as much oxidizing power, as nearly 4 liters of air. It should not be surprising, then, that liquid oxygen is capable of causing fires in materials that aren’t normally considered flammable, while materials which are known to burn in air will burn far more vigorously in atmospheres with increased oxygen concentration. Some materials may even ignite spontaneously on contact with liquid oxygen or in highly oxygen enriched atmospheres.
Hair, clothing, oil, grease, kerosene, tar, asphalt, and many plastics and rubbers will all burn readily in oxygen rich environments. In particular, cloth and clothing can trap oxygen gas in the porous weave of the fibers and remain incredibly prone to ignition long after the source of oxygen has been removed. Clothing that has been exposed to liquid oxygen will burn incredibly hot and fast if ignited, and will ignite more easily. All sources of ignition and incompatible materials must be kept away from liquid oxygen operations.
Vessels that contain liquid oxygen must be cleaned to very strict standards to ensure that no hydrocarbon or other incompatible contaminants are present. Oxidation of incompatible materials by liquid oxygen produces significant heat which causes the liquid oxygen to vaporize and expand quickly, potentially leading to the rupture of its container. The construction of a vessel to contain liquid oxygen must also avoid the use of any material which may oxidize or burn on contact with liquid oxygen. This makes liquid oxygen vessels unique in their construction. Liquid oxygen should never be added to any vessel of any type unless it is specifically constructed for use with liquid oxygen and has been cleaned according to strict protocols to ensure the complete removal of incompatible contamination.
Unlike every other cryogenic liquid, liquid oxygen does not pose an asphyxiation risk.
Both OSHA and Cal/OSHA have very strict regulations governing the design and construction of liquid oxygen installations. A thorough review by EHS personnel and the Fire Marshal will be required for any proposed work with cryogenic liquid oxygen.
