Tracer gas leak detection is a non-destructive method used to help locate hidden leaks in pipework. A safe tracer gas mixture, commonly hydrogen and nitrogen, is introduced into the system and specialist detection equipment is then used to identify where the gas escapes.
Tracer gas, often referred to as forming gas, is a safe, non-flammable mixture of approximately 95% nitrogen and 5% hydrogen. It is widely used for locating hidden leaks because the hydrogen molecules can escape through very small openings and be detected using specialist equipment.
It is one of several techniques used during leak investigations. The most appropriate method depends on the type of leak, the pipe material, the property construction and the evidence available on site. To explore related techniques, visit our Leak Detection Technology page. You can also view our main Leak Detection service page for a wider overview.
What Tracer Gas Leak Detection Is
Tracer gas leak detection involves introducing a hydrogen and nitrogen tracer gas mixture into a pipe system so that escaping gas can be detected at the surface. The gas mixture is safe, non-toxic and non-damaging to property when used correctly.
The gas can pass through very small openings in pipework. This makes it useful where a leak is hidden, where water is not visibly escaping, or where other leak detection methods have not provided a clear result.
How Tracer Gas Leak Detection Works
Before tracer gas testing begins, the pipework usually needs to be accessed, isolated and prepared. The gas is then introduced into the system under controlled conditions.
If there is a leak, the gas escapes through the leak point and moves through the surrounding material. Depending on the location of the pipe, this may include soil, screed, concrete, flooring, cavities or service routes.
- Tracer gas is introduced into the pipework.
- The gas escapes where the pipe is leaking.
- The gas moves through surrounding materials or voids.
- Detection equipment is used to identify where gas is present.
- The findings are interpreted alongside other evidence from the investigation.
This method can help identify leak locations even where there is no visible water at the surface.
When Tracer Gas Is Most Useful
Tracer gas leak detection is particularly useful where a leak is concealed, difficult to hear, or not producing a clear thermal pattern. It is often used when the leak location needs to be narrowed down without unnecessary excavation or damage.
It can be useful for:
- Leaks beneath solid floors or concrete floors.
- Buried water supply pipes.
- Plastic pipework where acoustic methods may be less effective.
- Leaks where water is not visibly appearing at the surface.
- Situations where acoustic testing is inconclusive.
- Investigations where the leak position needs to be confirmed before access or excavation.
Tracer gas is not required for every leak investigation. In some situations, other methods such as Acoustic Leak Detection, Thermal Imaging Leak Detection or Pressure Testing may be more appropriate.
What Tracer Gas Can and Cannot Tell You
Tracer gas can provide strong evidence that gas is escaping from a pipe system. However, the point where gas is detected is not always the exact point where the pipe is leaking.
Gas does not always travel directly upwards from the leak. It may follow the easiest route through the ground, a floor structure, a sleeve, a duct, a service void or another pathway within the property.
This is why tracer gas readings need to be interpreted carefully. The equipment detects gas, but the investigator must assess what the reading means in the context of the pipe route and the construction of the property.
Why Tracer Gas Readings Need Interpretation
Detecting tracer gas is only part of the process. The results still need to be interpreted correctly. An experienced leak investigator understands how gas can move through different parts of a property and uses this information, together with other test results, to identify the most likely leak location.
For example, water supply pipes are often installed within protective sleeves where they pass through or beneath foundations and enter a property. If a leak occurs outside the building, tracer gas can travel along the sleeve and emerge where the pipe rises through the floor. In that situation, a gas reading may be detected inside the property even though the leak itself is outside.
Similar effects can occur where there are service ducts, voids, cavities, waterproof membranes or other construction details that influence how gas moves. This does not mean the tracer gas test has failed. It means the findings need to be interpreted within the wider context of the investigation.
Limitations of Tracer Gas Leak Detection
Tracer gas can be highly effective, but it is not suitable for every situation and it should not be treated as a single guaranteed answer to every hidden leak.
Results can be affected by:
- Whether the pipework can be accessed and isolated.
- The depth of the pipework.
- Ground conditions and construction materials.
- Air movement and ventilation.
- Pipes running inside sleeves or ducts.
- Waterproof membranes, tanking systems or damp proof membranes.
- Voids, cavities or service routes that allow gas to travel away from the leak.
- Unknown or complex pipe routes.
These limitations are why tracer gas findings are often considered alongside other methods rather than being relied upon in isolation.
How Tracer Gas Fits With Other Leak Detection Methods
Tracer gas is often used as part of a wider leak investigation. It may help confirm a suspected leak location, test a section of pipework, or provide evidence where other techniques are limited.
It is commonly used alongside:
- Acoustic Leak Detection to assess leak noise from pressurised pipework.
- Thermal Imaging Leak Detection to identify temperature changes linked to water movement or heating pipework.
- Pressure Testing to confirm whether a system is losing pressure.
- Moisture Mapping to understand how water has moved through the property.
- Utility and Pipe Tracing where the route of buried pipework needs to be understood before testing or excavation.
The aim is not simply to get a reading from one piece of equipment. The aim is to build enough evidence to identify the most likely leak location and avoid unnecessary disruption.
Why Tracer Gas Leak Detection Matters
Tracer gas leak detection matters because it can help locate leaks that are hidden below floors, underground or within concealed pipework. It is especially useful where there is limited visible evidence and where unnecessary excavation or damage needs to be avoided.
Used correctly, tracer gas can provide valuable evidence during a leak investigation. Interpreted correctly, it can help narrow down the most likely leak location and support a more targeted repair or access plan.
Frequently Asked Questions
Can tracer gas find leaks under concrete floors?
Yes. Tracer gas is commonly used where leaks are suspected beneath solid floors or concrete floors. The gas can move through surrounding materials and be detected at the surface, helping to narrow down the likely leak location without extensive excavation.
Does tracer gas show the exact leak location?
Not always. Tracer gas provides evidence of where gas is escaping or emerging, but the reading still needs to be interpreted correctly. Factors such as pipe sleeves, service ducts, voids and construction details can influence where gas reaches the surface.
Is tracer gas suitable for every leak investigation?
No. Tracer gas is one of several techniques used during leak investigations. Depending on the circumstances, methods such as acoustic leak detection, pressure testing, thermal imaging or utility and pipe tracing may be more appropriate.
Need Help With a Hidden Leak?
Every leak investigation is different, and no single technology is suitable for every situation. The most effective approach depends on the type of leak, the pipe material, the construction of the property and the evidence available on site.
To learn more about hidden leak investigations, visit our Leak Detection hub page. If you need advice about a suspected leak or would like to discuss an investigation, please contact us and we will be happy to help.
