Trace Gas Guide
Choose helium, hydrogen forming gas, argon or air by selecting the least expensive gas that reliably meets the reject limit.
A trace-gas test fills a sealed part with a gas the detector can measure, then measures the gas that escapes. The decision starts with the reject limit, then considers the method, gas availability and the production environment.
Helium reaches the smallest leak paths, hydrogen forming gas offers sensitive sniffing at lower operating cost, argon provides an atmospheric alternative, and air uses the supply already plumbed to many lines.
Choose the gas and detection method together. Sniffing localizes a leak, hard vacuum reaches the smallest rates, accumulation measures gas collected around a part, and bombing supports sealed devices that cannot be connected directly.
Request for QuoteTrace gas leak testing detects an escaping tracer rather than inferring a leak from a pressure change. The selected gas is introduced into the part, and the detector measures the signal where the gas leaves the sealed volume.
For the method sequence, detector setup and application details, visit the trace gas leak testing method page. This guide focuses on the gas selection decision.
A gas choice does not replace fixture design or a controlled sequence. It determines the signal available to the detector, while the selected method determines whether the station scans a seam, measures a chamber, uses vacuum or verifies a sealed package.
Benchmark
Helium is inert, non-toxic and non-flammable. Its atmospheric background is about 5 ppm, which keeps background interference low.
Workhorse
Forming gas is 5% hydrogen and 95% nitrogen. It is non-flammable, inexpensive and widely available.
No-supply-risk alternative
Argon makes up nearly 1% of the atmosphere and is produced in bulk as a byproduct of air separation.
Drop-in upgrade
Clean, dry compressed air already used on a line can act as the tracer for air-based detection.
| Selection factor | Helium | Forming gas | Argon | Air |
|---|---|---|---|---|
| Typical sensitivity | 10⁻⁹–5×10⁻¹² hard vacuum; ≈10⁻⁷ sniff | ≈10⁻⁷ sniff | ≈10⁻⁶ | ≈10⁻⁴ |
| Atmospheric background | About 5 ppm | Disperses after testing | Nearly 1% | Available on the line |
| Cost & supply | Pricing and availability can vary | Inexpensive and widely available | Bulk air-separation byproduct | No cylinder supply |
| Safety | Inert, non-toxic, non-flammable | 5% H₂ / 95% N₂; non-flammable | Inert | Clean, dry compressed air |
| Detection methods | Hard vacuum, sniffing, accumulation, bombing | Sniffing | Argon-capable detection | Air-based detection |
| Best for | Smallest leak paths | High-throughput sensitive sniffing | Industrial leak specs | Pressure-decay-like limits |
Connect the part to the fixture and establish the seal before gas flows.
Introduce the selected gas using the programmed sequence.
Run the selected trace-gas method and measure the detector response.
Store the quantitative result and pass/fail decision for the part.
Air avoids cylinder supply, while argon is inexpensive and produced in bulk through air separation.
Helium hard vacuum reaches 10⁻⁹–5×10⁻¹² mbar·l/s; helium sniffing reaches about 10⁻⁷ mbar·l/s.
The forming gas described here is 5% hydrogen in 95% nitrogen and is non-flammable.
Yes. Clean, dry compressed air can reach roughly 10⁻⁴ mbar·l/s with air-based detection.
High-volume helium users may add recovery when helium pricing and availability are a concern.
Argon fits industrial leak specifications that need roughly 10⁻⁶ mbar·l/s sensitivity without a helium supply.
Select the gas and method together around the reject limit and whether the application needs localization, vacuum detection, accumulation or bombing.
Compare trace gas with pressure, vacuum and flow methods in the leak test method chooser. For an air-based route, see the pressure-decay buyer’s guide.
For HVAC and refrigeration components, see HVAC & Refrigeration Leak Testing for peer air and trace-gas production method routing.
SniffingScan the seam to localize an escaping tracer.
Hard vacuumMeasure helium under vacuum for fine-leak detection.
AccumulationMeasure tracer collected around the part.
BombingVerify sealed devices without a direct connection.
Z-ChargePrepares and charges the part for the trace-gas sequence.
Z-IonHelium detector for sniff and vacuum testing.
Z8Runs air-based methods alongside production testing.
