Gas leak detection tries to locate escaping gas; a tightness test evaluates whether a defined section holds pressure according to an approved method. These tasks use different instruments and acceptance criteria. A handheld detector can help find a suspected leak point, but its alarm cannot establish that an entire gas system meets a pressure-tightness requirement.
A positive detector finding is not a measured leak rate
An electronic gas detector can help localize an escaping gas but usually does not prove that a closed system holds pressure. A tightness test can reveal a pressure change without identifying the exact defect location. Both results depend on approved test media, environment and leak-search procedures, particularly for flammable refrigerants or fuel gas.
Different questions, different evidence
| Method | Question answered | Typical observation |
|---|---|---|
| Leak localization | Where is combustible gas detected? | Detector response near fittings or joints |
| Pressure tightness test | Does an isolated section meet its specified hold/test criterion? | Pressure change under defined time and temperature conditions |
| Combustion flue-gas spillage check | Are combustion products escaping into an occupied area? | Appropriate flue-gas/spillage detector indication |
Why a detector does not replace a pressure test
A portable gas detector responds to gas near its sensor under the current airflow, background concentration and sensitivity setting. A joint might leak intermittently or disperse gas away from the measurement point. Conversely, a pressure test evaluates the defined volume over a test period; its result can be affected by system temperature, gauge performance and isolation quality. For a broader explanation of pressure references and instrument types, see pressure measuring instruments.
Professional inspection workflow
- Identify the fuel gas, installation type and governing code before selecting a testing method.
- Follow the site’s isolation, ventilation and emergency procedures. Suspected active leaks call for immediate qualified response rather than informal testing.
- For localization, use a detector specified for the gas and environment and follow its documented check and survey procedure.
- For tightness, qualified personnel use a calibrated pressure instrument, test medium and specified duration/pressure under the applicable standard.
- Record temperature, pressure, start/end time and the exact section tested.
- Investigate failures and repeat testing only under the approved procedure.
Hypothetical temperature effect
In a sealed idealized gas volume, absolute pressure changes with absolute temperature even without leakage. If a closed system were at 293 K and cooled to 290 K, its absolute pressure would decrease by approximately 1.0%, all else equal. This illustration is not a test protocol; real systems and gauge pressures require the specified correction and conditions.
Two different Testo instruments
The testo 316-1 is a methane/natural-gas leak locator with audible and visual indications. The testo 312-4 is a differential-pressure instrument designed for defined pressure and tightness testing workflows on suitable pipe systems. Neither replaces the site’s code-required procedure or gas emergency response.
When to stop
Do not enter or remain in a suspected dangerous gas atmosphere to gather readings. Evacuate and contact emergency or licensed gas professionals according to local instructions. Never defeat regulators, alarms or gas safety controls for a test.