Oxygen:

Oxygen (O₂) supports combustion, other than does not burn. Even so, it has to be considered a potentially hazardous component from a fire hazard standpoint.  The conclusion of an enriched oxygen atmosphere involves a lowered ignition temperature, a rise flammable range, or an acceleration of the burning rate. Oxygen readily combines along with other compounds and elements, along with spontaneous ignition within some cases. While oxygen comes within contact along grease, with oil, or fuel oils, it may ignite violently. Each possible precaution must be taken to avoid this combination.

Oxygen sustains life, other than if pure oxygen were inhaled continuously for extended periods; the reactions in the body would be too rapid and would cause harmful effects.  It should always be referred to as oxygen, and not air, to avoid confusion.  Oxygen should never be used to run pneumatic equipment since of the possibility of coming within contact along with oil which might be inside the equipment.  At last, oxygen valves should be operated slowly.  Abruptly beginning and stopping oxygen flow might ignite contaminants in the system.