The administration of medical gases to patients is subject to a variety of hazards that can result from human error due to preoccupation, a mental lapse, or carelessness. This publication was developed to reduce the possibility of inadvertent substitution of the wrong medical gases by personnel when using equipment for administering anesthesia, resuscitation, and therapy.

CGA V-1, Standard for Compressed Gas Cylinder Valve Outlet and Inlet Connections, establishes assigned standard connections for threaded outlets on cylinder valves, which results in the removal from service of all cylinder valves having nonconforming threaded outlets. CGA V-1 also describes the details of the Pin Index Safety System for flush-type medical gas cylinder valves. This system reduces the possibility of inadvertent substitution of the wrong gases on equipment with yoke-type connections. The Pin Index Safety System has been adopted by national and international standards organizations including the Canadian Standards Association (CSA) and the International Organization for Standardization (ISO).

The Diameter Index Safety System defines noninterchangeable removable connections for use with medical gases at pressures of 200 psi (1380 kPa) or less. Removable, threaded connections are readily and commonly engaged or disengaged in routine use and service and are often found on regulators, resuscitation equipment, anesthesia equipment, therapy equipment, and other similar equipment.

The Diameter Index Safety System supplements but does not replace:

• any of the means for medical gas identification currently in use;
• the Pin Index Safety System;
• the existing threaded outlet standards for cylinder valves; or
• automatic quick coupler valves that also provide noninterchangeable connections for medical gases and suction equipment.

CGA does not designate where the Diameter Index Safety System should be applied.