7.1 Installer Tests I: Blowdown, Initial Pressure, Cross-Connection & Piping Purge
Key Takeaways
All installer-performed tests use oil-free, dry nitrogen NF as the test gas.
Blowdown clears the distribution piping after it is installed but before station outlet rough-ins, alarm devices, indicators, relief valves, manifolds, and source equipment go in.
The initial pressure test holds each section at 1.5 times operating pressure, never below 150 psi, with the source valve closed, while every joint is checked with an oxygen-safe, ammonia-free leak detectant.
For the cross-connection test, every system is reduced to atmospheric pressure, only the system under test is charged to 50 psi with nitrogen, and each outlet and inlet is checked with matching adapters.
The initial piping purge test flows intermittent, high-volume nitrogen through each outlet until a clean white cloth shows no discoloration, starting nearest the zone valve and working outward.
Which Systems Must Be Tested
NFPA 99 requires inspection and testing of new piped medical gas and vacuum systems and of additions, renovations, temporary installations, and repaired systems. A system is considered breached wherever the pipeline is entered, whether by physical separation or by removing, replacing, or adding a component. The tests are performed by the installer first and then by an independent verifier. This section and the next cover the installer's tests. Their test gas is always oil-free, dry nitrogen NF.
Test 1: Initial Piping Blowdown
When: after the distribution piping is installed, but before station outlet/inlet rough-in assemblies and other components are installed. Those components include pressure and vacuum alarm devices, pressure and vacuum indicators, pressure relief valves, manifolds, and source equipment.
How: blow the piping clear with oil-free, dry nitrogen NF.
Why before components: chips, dust, or a stray deburring curl blown down the pipe should come out an open end, not lodge in an alarm switch, a relief valve, or an outlet's secondary valve seat.
Test 2: Initial Pressure Test
| Item | Requirement |
|---|---|
| Scope | Each section of piping, in both gas and vacuum systems |
| Timing | After blowdown, after the station outlet/inlet rough-in assemblies are installed, and before components that test pressure would damage, such as alarm devices, indicators, and line pressure relief valves |
| Source valve | Remains closed |
| Test pressure | 1.5 times the system operating pressure, but not less than 150 psi gauge. This applies to vacuum systems too. |
| Leak check | Hold pressure until each joint has been examined with a leak detectant that is safe for oxygen and contains no ammonia |
| Leaks | Locate them, repair (where permitted) or replace, and retest |
| Witness | An ASSE 6020 inspector, an ASSE 6030 verifier, or the AHJ or its designee; a form documenting the witnessed test goes to the verifier at the start of verification |
Calculating the initial test pressure
| System | Operating pressure | 1.5 times operating | Test pressure used |
|---|---|---|---|
| Oxygen | 55 psi | 82.5 psi | 150 psi (the minimum governs) |
| Medical air | 50 psi | 75 psi | 150 psi |
| Nitrogen | 185 psi | 277.5 psi | 277.5 psi |
| Instrument air | 160 psi | 240 psi | 240 psi |
| Medical-surgical vacuum | (vacuum) | — | 150 psi minimum pressure test |
Warning
Ammonia-based leak detectors and household soaps are not acceptable. NFPA 99 requires a leak detectant safe for use with oxygen that does not contain ammonia. Ammonia attacks copper alloys and can cause stress-corrosion cracking of brass and bronze components.
Test 3: Initial Cross-Connection Test
The goal is to prove that no cross-connections exist between the different medical gas and vacuum systems:
- Reduce all piping systems to atmospheric pressure.
- Disconnect all test gas sources except from the one system being tested.
- Charge the system under test with oil-free, dry nitrogen NF to 50 psi.
- With the individual faceplates installed and adapters matching each outlet or inlet label, check every outlet and inlet in every installed system. Test gas must come only from the outlets of the system being tested.
- Repeat for each installed medical gas and vacuum system.
- Confirm proper labeling and identification of outlets and inlets during the test.
Testing systems one at a time with all others empty is the whole point. If the medical air system holds 50 psi and gas comes out of an oxygen outlet, there is a crossed pipe somewhere. That is exactly the error that has delivered the wrong gas to patients.
Test 4: Initial Piping Purge Test
| Item | Requirement |
|---|---|
| Purpose | Remove particulate matter from the distribution piping |
| Method | Using appropriate adapters, purge each outlet with an intermittent, high-volume flow of test gas until the purge produces no discoloration in a clean white cloth |
| Order | Start at the outlet closest to the zone valve and continue to the farthest outlet in the zone |
Purging from nearest to farthest moves debris along the pipe and out, rather than pushing it back into sections that were already cleared.
How These Tests Fit Together
- Blow down the bare piping.
- Install outlet rough-ins and pressure test every section at 150 psi minimum, with the joints witnessed.
- Install the remaining components.
- Run the 24-hour standing tests (Section 7.2).
- Install faceplates and run the cross-connection test and the purge.
Throughout, keep nitrogen in the lines and openings sealed, so moisture and dust do not get back in.
Record Keeping
Record the date, the system, the test pressure, who performed the test, who witnessed it, and the result for each test. The witness form for the initial pressure test, and the forms for the 24-hour standing tests, must be given to the verifier at the start of verification. A verifier cannot begin without them.
What initial pressure test pressure does NFPA 99 require for an oxygen system that operates at 55 psi?
82.5 psi
66 psi
150 psi
110 psi
How is the installer's initial cross-connection test set up?
Every system is charged to 50 psi at the same time, and then each outlet is checked for odor with an analyzer
All others at atmospheric pressure, one system at 50 psi nitrogen, every outlet checked with matching adapters
Each system is charged with its own source gas at normal line pressure and checked only at its zone valve
The vacuum system is run while the gas systems are pressurized
When performing the installer's initial piping purge test in a zone, where should the installer start?
At the outlet closest to the zone valve, then out to the farthest
At the outlet farthest from the zone valve, then work back toward the valve
At any outlet, in any order, as long as each one is eventually purged clean
At the source valve, then each riser
Sections you finish are checked off in the contents.