You need a gas tightness test after any work on commercial gas pipework that could affect whether it is gastight, and before appliances are put into service. Purging follows a successful test: it removes the air and any other gas from the pipework so only the gas to be supplied remains and appliances can be lit safely.
Both are set out in law, in regulation 22 of the Gas Safety (Installation and Use) Regulations 1998, and in industry standards published by IGEM, the Institution of Gas Engineers and Managers. This guide explains what each involves, when you need it and what you should get at the end.
What a tightness test is
A gas tightness test, sometimes called a soundness test, confirms that a section of gas pipework holds pressure with no leaks from the pipes, fittings or connections. The engineer isolates the section being tested, applies a test pressure, monitors it over a set period and confirms whether the installation holds that pressure within the expected limits.
If it does not pass, the engineer investigates where the leak is and explains it before deciding on the remedy. A failed test is useful information: it tells you there is a problem before gas is put back into the pipework, not after.
A tightness test is not the same as a gas safety inspection. It checks the pipework, not the appliances, and it is a procedure in its own right, with its own record: the CP16.
When you need a tightness test
- After new pipework is installed. Regulation 22 requires pipework to be tested for gastightness immediately after any work that might affect it.
- After any alteration. Adding a branch, moving an appliance or replacing a valve is work on the pipework, so the same rule applies.
- After a leak is repaired. The repair is work on the pipework, so the installation is tested again before it goes back into use.
- Before commissioning or recommissioning. New plant, or plant brought back into use, is not commissioned until the pipework is confirmed sound.
- As a standalone check. You can ask for a test on an existing installation, for example when you take over a building or before a refurbishment.
Which standard applies depends on the installation. IGEM/UP/1 covers strength testing, tightness testing and direct purging of industrial and commercial gas installations. IGEM/UP/1A covers small, low-pressure industrial and commercial installations, and IGEM/UP/1B covers small installations. Your engineer will tell you which tests apply.
What purging is
Purging replaces the contents of the pipework safely. Under regulation 22, when gas is supplied to pipework that has been worked on, it must be purged after testing so that all air and any gas other than the gas to be supplied is removed safely. If the pipework is not going into use straight away, every outlet is sealed off, and those seals are tested for gastightness.
Pipework that is no longer needed is a separate job. Redundant pipework needs to be safely decommissioned rather than left in the building, and we plan that as part of the same gas work.
The right order
On a typical project the sequence is: install or alter the pipework, tightness test it, purge it, then commission the appliances. Each step depends on the one before. If the test fails, the installation is not purged. If the purge is not complete, appliances are not lit.
That sequence matters most on a plant room replacement, where a new gas service, new boilers and new controls all come together. At New Wimbledon Theatre, ComGas isolated, purged and altered the gas service as part of a full plant room refurbishment. The new installation included a gas isolation and solenoid arrangement, gas-pressure proving and detection, and emergency gas shut-off, serving three new Hamworthy Purewell boilers.
What you should get at the end
You should get the result in writing. For a tightness test, that is a pass, or the fault found and the next steps. For the testing and purging it carries out, ComGas issues a gas testing and purging record (CP16). Keep it with your building records so the next engineer can see what was done.
Planning the work around your building
The section being tested is isolated, so appliances on it are off during the test. In a school, a kitchen or a care home that needs planning. Agree the timing in advance, keep the isolation as short as possible and combine testing and purging with other gas work, so you have one shutdown rather than several.
Key facts
- Regulation 22 requires a gastightness test immediately after any work that might affect the pipework’s gastightness.
- A tightness test confirms the pipework holds pressure over a set period with no leaks.
- Purging removes air and other gas so only the gas to be supplied remains.
- The order is: install or alter, test, purge, then commission.
- IGEM/UP/1, UP/1A and UP/1B set out the procedures for different sizes of installation.
- In workplaces such as shops, restaurants, schools and hospitals, gas work must be done by a Gas Safe registered engineer qualified for the work.
- Ask for the result in writing: a gas testing and purging record (CP16). Keep it with your building records.
Frequently asked questions
Is a tightness test the same as a gas safety inspection?
No. A tightness test checks the pipework holds pressure. A gas safety inspection checks the appliances, flues and safety devices. They are different procedures, though they can be done on the same visit.
What happens if the test fails?
The installation stays out of use. The engineer investigates the leak, explains it and agrees the repair with you. After the repair, the installation is tested again before it goes back into service.
Will the gas be off during testing?
Yes, for the section being tested. We agree the timing with you in advance and plan around trading hours, occupancy and term dates.
Do I need a test if no work has been done?
Not always, but a standalone test is a sensible check when you take over a building, before a refurbishment, or if you are unsure of an installation’s condition. If you smell gas, turn off the supply if it is safe to do so and call the National Gas Emergency Service on 0800 111 999.
Talk to us about testing
ComGas carries out gas tightness testing and purging on new, altered and existing commercial installations across Surrey and the surrounding counties, as a standalone visit or as part of wider work. Read more about our commercial gas tightness testing, or call 01252 214120.