Pneumatics are similar to hydraulic systems except that they use pressurized air or gas instead of liquid. There are both manual and automatic systems available. Some advantages of pneumatic over hydraulic systems are long operating lives, little maintenance required, less subjective to shock damage, less chance of fire compared to hydraulic oil. The two types of gases used in pneumatic systems are oxygen free nitrogen (OFN), and carbon dioxide (CO2). These gases are asphyxiation hazards and are highly flammable when concentrated. In the case of CO2 improper discharge is a freezing hazard. Because of this most pneumatic systems are supported with compressed ambient air. Generally only small tools are powered with compressed cylinders of CO2 and OFN gas. Pneumatic mechanisms have been around since the dawn of man. Whistling for instance is a pneumatic operation. Pipe organs, harmonicas, and almost all musical instruments use pneumatic principles to create music. In the modern industrial setting we use pneumatics in machines such as air guns, internal mail systems, nail guns, race cars, and vacuum pumps just to name a few.