I breathe in air all day long.
What do you mean it’s hazardous?
Air is considered to be a hazardous material when it’s packaged in a cylinder because it’s under pressure.
All gases can present a potential hazard because they are under pressure. Every cylinder has a pressure rating for its maximum filled pressure. Depending on the pressure rating of the cylinder and the system components, compressed gases may be pressurized in excess of 6000 psig. It is important to always use the appropriate pressure regulating and pressure relief devices to prevent over-pressurization and potential catastrophic failure to containers and/or piping.