A gas cylinder is a containment apparatus that will store a gaseous compound under pressure for use in medical settings. The physical form of the stored compound can be gas or liquid, with the ultimate output from the apparatus being gaseous. Gas cylinders allow for the portable and safe storage of compounds needed in a medical setting. The sizing of gas cylinders has been attributed to a nationally recognized letter, with the more commonly used medical sizes listed below. Gas cylinders are labeled from A to M, with increasing volume as the letters of the alphabet proceeds. The E-sized cylinders are the most commonly used size in medical settings. An E cylinder has a service pressure of 1900 psi but may be filled up to 10% more to 2200 psi. Higher filling pressure allows for expansion at temperatures greater than 70 degrees Fahrenheit