Quick answer
A gas tightness test proves that gas pipework and fittings are not leaking, by pressurising the installation and monitoring for any pressure drop over a set time. Businesses need one after new pipework is installed, after work on existing pipework, after a gas escape, and before gas is turned back on. Commercial installations are tested to IGEM/UP/1 or IGEM/UP/1B.
How a tightness test works
The engineer isolates the section of installation being tested, connects a suitable pressure gauge, and raises or holds the pipework at a test pressure. After a period to let the pressure stabilise, the gauge is monitored for a set test duration. The permitted pressure drop, if any, depends on the installation volume, the gas, the gauge used and whether the pipework is new or existing. If the test fails, the leak must be found and repaired and the test repeated.
Before gas is reintroduced, pipework that has been opened or is new must be purged safely of air, and appliances are then commissioned or relit.
Which standard applies?
- IGEM/UP/1 covers strength testing, tightness testing and direct purging of industrial and commercial gas installations.
- IGEM/UP/1A covers strength testing, tightness testing and direct purging of small, low-pressure industrial and commercial natural gas installations.
- IGEM/UP/1B covers tightness testing and direct purging of small natural gas, LPG and LPG/air installations, typically within limits on pipe diameter, installation volume and pressure. It is often used on smaller commercial premises.
- BS 6891 covers the installation of low-pressure gas pipework (up to 35 mm) in domestic premises, and domestic tightness testing follows gas industry procedures. Larger pipework is designed to IGEM/UP/2.
Which procedure is right depends on installation volume, operating pressure and pipe size. The engineer works out the installation volume and selects the correct procedure before testing.
When does a business need a tightness test?
- After new gas pipework is installed, before it is brought into use (along with a strength test where required).
- After any work that breaks into existing pipework, such as adding or moving appliances.
- When a gas escape is reported or suspected.
- Before turning gas back on after it has been isolated or the meter changed.
- As part of routine inspection and maintenance, and before issuing commercial gas safety records.
- When taking over or fitting out premises, so you know the installation is sound.
What the law says
The Gas Safety (Installation and Use) Regulations 1998 require gas work to be carried out by a competent, Gas Safe registered person, and require installations to be tested for gas tightness after work on gas fittings. Employers also have duties under health and safety law to maintain gas systems in a safe condition.
What you get after the test
A competent engineer records the procedure used, test pressures, durations, results and any remedial action. Keep it with your other gas safety records; insurers, landlords and inspectors may ask for it.
Commercial kitchens
Kitchens often combine tightness testing with checks on the ventilation interlock and appliance safety devices. See our guide to commercial kitchen gas interlocks.
CombiCert in Telford
CombiCert Ltd is a Gas Safe registered (621146) gas and heating company based at The Old School House, Park Lane, Telford TF3 4TG, working across Telford and Shropshire for homes and businesses. We are open Monday to Saturday, 08:00 to 19:45 (closed Sunday).
Commercial tightness testing: call for a quote on 07393 220694. Domestic gas pipe check £80 + VAT.
See Light commercial gas services for details, or call or WhatsApp 07393 220694, or email hello@combicert.co.uk.
Frequently asked questions
How long does a commercial gas tightness test take?
It depends on the installation volume, the gauge used and the procedure. Small commercial installations may take under an hour including stabilisation and test periods. Large installations, or those needing a strength test, purging or leak tracing, take longer. The engineer calculates timings from the relevant IGEM procedure.
What is the difference between IGEM/UP/1 and IGEM/UP/1B?
IGEM/UP/1 covers strength testing, tightness testing and purging of industrial and commercial gas installations generally. IGEM/UP/1B is for smaller natural gas and LPG installations within set limits on size, volume and pressure. The engineer calculates the installation volume to decide which procedure applies.
What happens if my gas installation fails a tightness test?
The engineer will make the installation safe, which may mean isolating the supply. The leak must be found and repaired, and the test repeated until it passes before gas is restored. If there is an immediate danger, the engineer follows the Gas Industry Unsafe Situations Procedure.
Do I need a tightness test before a new appliance is fitted?
Yes. Gas Safe engineers carry out a tightness test before and after work on gas fittings, including connecting a new appliance. Testing before work establishes that the installation is sound; testing afterwards proves that the new connection and any altered pipework are not leaking.
Can any Gas Safe engineer do a commercial tightness test?
No. The engineer must be registered with Gas Safe for commercial work and hold the relevant competence for commercial tightness testing and purging. Check the back of their Gas Safe ID card, which lists the categories of gas work they are qualified to carry out.
This guide is general information, not a substitute for an on-site assessment by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.