7.4 Tie-Ins, Breached Systems, Operational Flow & Gas Concentration Tests
Key Takeaways
A system is breached at the point of pipeline intrusion, and retesting covers the altered zone plus components in the immediate area: downstream of the intrusion for pressure gases, upstream for vacuum.
Each joint in a final tie-in is leak-tested with the system gas at normal operating pressure, using an oxygen-safe, ammonia-free leak detectant; vacuum joints are tested with an ultrasonic leak detector or a similar method.
After a pressure-gas tie-in, an outlet in the new piping and one in the existing piping immediately downstream are purged, then operational pressure and concentration tests are run before patient use.
Every 50 psi gas outlet must deliver 3.5 SCFM (100 SLPM) with no more than a 5 psi drop, and every vacuum inlet must draw 3 SCFM without dropping an adjacent inlet below 12 in. HgV.
Concentration criteria: Oxygen USP at least 99%, Oxygen 93 USP 90-96%, nitrous oxide at least 99%, nitrogen NF at most 1% oxygen, and medical air 19.5-23.5% oxygen.
Breached Systems: How Much Must Be Retested?
NFPA 99 requires inspection and testing of any system that is breached and of components that are added, renovated, or replaced. Examples include new gas sources such as bulk systems, manifolds, compressors, dryers, and alarms.
- A system is breached at the point of pipeline intrusion, whether by physical separation or by removing, replacing, or adding a component.
- Inspection and testing are confined to the specific altered zone plus the components in the immediate zone or area. That means upstream of the intrusion for vacuum systems and downstream for pressure gases.
Example: adding two new oxygen outlets to an existing patient room zone breaches the oxygen piping in that zone. The new piping gets the installer tests. The zone downstream of the intrusion point, including existing outlets in that zone, gets the applicable verification tests. Unaffected zones on other floors do not.
The Final Tie-In Test
The final connection of new work to a live system is often brazed without a nitrogen purge, as Section 3.2 allows, because the existing line still holds system gas. NFPA 99 compensates with the final tie-in test:
| Step | Requirement |
|---|---|
| 1. Leak test | Each joint in the final connection is leak-tested with the gas of system designation at the normal operating pressure, using a leak detectant safe for oxygen with no ammonia |
| 2. Vacuum joints | Tested with an ultrasonic leak detector, or another method that detects leaks in an active vacuum system |
| 3. Purge (pressure gases) | Immediately after the connection is made and leak-tested, purge an outlet in the new piping and an outlet in the existing piping that are immediately downstream of the intrusion, using a heavy, intermittent purge |
| 4. Before patient use | Positive-pressure gases are tested for operational pressure and gas concentration |
| 5. Records | Permanent records of these tests are kept |
Operational Flow Pressure Drop Test
This test is performed at each station outlet or inlet, or terminal, where the user makes connections and disconnections, using the gas of system designation or the operating vacuum.
| Terminal | Required performance |
|---|---|
| Gas outlets at 50 psi (oxygen, nitrous oxide, medical air, carbon dioxide, and others) | Deliver 100 SLPM (3.5 SCFM) with a pressure drop of no more than 5 psi, at a static pressure of 50-55 psi |
| Medical support gas outlets (nitrogen, instrument air) | Deliver 140 SLPM (5.0 SCFM) with a drop of no more than 5 psi, at a static pressure of 160-185 psi |
| Medical-surgical vacuum inlets | Draw 85 NL/min (3 SCFM) without reducing vacuum at any adjacent inlet below 12 in. HgV |
| Oxygen and medical air outlets serving Category 1 spaces | Allow a transient flow of 170 SLPM (6 SCFM) for 3 seconds |
Reading a result: an oxygen outlet holds 54 psi static and drops to 48 psi while flowing 3.5 SCFM. The drop is 6 psi, which exceeds the 5 psi limit, so the outlet fails. Typical causes are an undersized drop, a partly closed in-line valve, debris in the secondary valve, or a kinked flexible connector in a headwall.
Medical Gas Concentration Test
After each system is purged with its gas of system designation:
- Each pressure gas source and outlet is analyzed for gas concentration by volume.
- The analysis uses instruments designed to measure the specific gas dispensed.
- Results must meet the table below.
| Gas | Acceptable concentration |
|---|---|
| Oxygen USP | At least 99% oxygen |
| Oxygen 93 USP | 90% to 96% oxygen |
| Nitrous oxide USP | At least 99% nitrous oxide |
| Nitrogen NF | No more than 1% oxygen, or at least 99% nitrogen |
| Medical air USP | 19.5% to 23.5% oxygen |
| Other gases | Named gases within plus or minus 1%, or per specification |
Why every outlet? The concentration test is the final proof against a cross-connection. It also catches an outlet still holding nitrogen test gas after the system was switched to oxygen. A patient connected to such an outlet would receive nitrogen. An oxygen outlet reading 97% fails Oxygen USP. It passes only if the system is designed to supply Oxygen 93 USP from concentrators, where 90-96% is acceptable.
Planning Tie-Ins in Occupied Facilities
- Coordinate shutdowns with the responsible facility authority and clinical staff. Use zone valves and service valves to limit the affected area, and arrange portable cylinders or auxiliary connections for patients who need gas during the work.
- Contain debris when breaching live piping. NFPA 99 requires breaching methods that leave no particles in the pipe and keep debris in the work area.
- Some jurisdictions add other requirements. For example, the California Plumbing Code requires plumbing work in existing, occupied inpatient facilities to be done by personnel certified to ASSE 12010 (infection control).
- Do not return the zone to service until the final tie-in, purge, operational pressure, and concentration results are in hand and documented.
A crew makes the final brazed tie-in of a new oxygen branch to a live main without a nitrogen purge. How must each joint in that connection be leak-tested?
With nitrogen at 150 psi, brushing any household dish soap solution onto every joint
With system gas at operating pressure, using an oxygen-safe, ammonia-free detectant
By a 24-hour standing pressure test of every medical gas system in the whole building
By listening for leaks with the zone valves open
During the operational flow pressure drop test, a medical-surgical vacuum inlet is flowing 3 SCFM. What must remain true?
The inlet under test stays above 19 in. HgV
The vacuum source runs at no more than 50% capacity
No adjacent station inlet drops below 12 in. HgV
The area alarm does not activate for 3 seconds
What concentration result is acceptable at an outlet of a medical air system during the gas concentration test?
19.5% to 23.5% oxygen
At least 99% oxygen
90% to 96% oxygen
No more than 1% oxygen
Sections you finish are checked off in the contents.