5.3 Station Outlets & Inlets, Manufactured Assemblies & Pressure Indicators

Gas-Specific Means Physically Impossible to Misconnect

NFPA 99 requires each station outlet and inlet for medical gases or vacuum to be gas-specific, whether it is a threaded connection or a noninterchangeable quick coupler:

• Threaded outlets and inlets must be noninterchangeable connections that meet the mandatory requirements of CGA V-5, the Diameter Index Safety System (DISS). DISS uses different diameter combinations for each gas, so an oxygen fitting cannot be threaded onto an air outlet.
• Quick couplers use gas-specific keys, pin spacings, or shapes.
• Gas-specific parts must be impossible to interchange between outlets for different gases. This applies to outlets in columns, hose reels, ceiling tracks, and other special installations too.
• Common parts such as springs, O-rings, fasteners, seals, and shutoff poppets may be shared across gases, because they do not affect gas-specificity.
• Vacuum inlet components needed to keep the inlet vacuum-specific must be marked as vacuum or suction parts. Inlet components that are not vacuum-specific need no marking.

Valves Inside the Outlet

The secondary valve is what lets a technician remove a damaged outlet's primary assembly without shutting down the whole zone.

Nonstandard Operating Pressures

Where a station outlet operates at a pressure other than the standard pressure for its gas, it must be:

1. Gas-specific
2. Pressure-specific where one gas is piped at more than one pressure. An oxygen outlet at 80 psi must not accept a 50 psi oxygen adapter.
3. DISS, or meet item 4, if operated above 80 psi
4. Designed so the adapter cannot be removed until the pressure has been relieved, if operated at 200 to 300 psi. This protects the user from an adapter blown out under pressure.

Support gas outlets, such as nitrogen at 160-185 psi, are therefore normally DISS.

WAGD Inlets

Station inlets for WAGD must:

• Not be interchangeable with any other system, including medical-surgical vacuum
• Have WAGD-specific components legibly marked as WAGD inlet components
• Suit the flow and vacuum level required by the facility's anesthesia gas machines
• Be located to avoid physical damage

Factory Tubes, Spacing and Protection

Outlets are also labeled with the gas name or symbol and color code (Section 5.5). In sleep labs, where an outlet is downstream of a flow control device, the outlet label must warn not to use it for ventilating patients.

Where Outlets Fit in the Installation Sequence

1. Blow the piping clear with nitrogen NF before the outlet rough-in assemblies are installed.
2. Install the rough-in assemblies, then run the initial pressure test.
3. Install the outlet valve bodies and faceplates, then the 24-hour standing pressure test.
4. The cross-connection test uses adapters that match each outlet's label, with faceplates installed.

Manufactured Assemblies

Manufactured assemblies are factory-built devices such as headwalls, columns, booms, pendants, and medical gas rails (MGR) that arrive with outlets and internal piping already installed. NFPA 99 sets leakage limits for them, requires their components to meet flame-spread or combustibility limits, and requires MGR assemblies to connect to the pipeline through brazed fittings. Columns, booms, pendants, and similar special installations must be on the patient side of their zone valve. Hoses inside these assemblies must follow the flexible connector rules: no longer than necessary and never concealed in walls, floors, or ceilings.

Pressure and Vacuum Indicators

Indicators must be readable from a standing position. At a minimum, they are required:

1. Next to the alarm-initiating device for the source main line pressure and vacuum alarms in the master alarm system
2. At or in area alarm panels, to show the pressure or vacuum at the alarm sensor for each system that panel monitors
3. On the station outlet/inlet side of each zone valve

Indicators and alarm sensors are among the few devices that may use threaded connections, often through gas-specific demand check fittings. Those fittings let the device be removed without shutting down the line. They are installed after the initial pressure test, because test pressure could damage them.