When does a business need a gas tightness test (CP16)?
A business needs its gas pipework tested for tightness, and usually purged, whenever work is done that could affect it: a new supply or meter, new or extended pipework, an alteration, or the gas being turned back on to a unit that has been capped off. The test proves the pipework holds gas without leaking. The purge clears air out of the pipes, or gas out of pipes being taken out of use, so nothing unsafe is left inside. At business premises the result is usually recorded on a CP16.
What the law asks
Regulation 22 of the Gas Safety (Installation and Use) Regulations 1998 covers testing and purging. Anyone who does work that might affect the gas tightness of an installation must test it for tightness straight afterwards, at least as far as the nearest valves on either side of the work. When pipework is purged, it must be done safely, so that no air or unwanted gas is left in it and none escapes where it could cause harm.
How the test and the purge are carried out at business premises is set out in the Institution of Gas Engineers and Managers standards:
- IGEM/UP/1 for commercial and industrial installations of any size
- IGEM/UP/1A for smaller low pressure installations, up to 1m³ of pipework volume at an operating pressure of up to 40 mbar
The CP16 is the industry’s usual form for recording the work. Like the CP17 and the CP42, it is not named in law. It is how the business shows the test and purge were done.
When the test is needed
| Situation | What is usually needed |
|---|---|
| New gas supply, new meter or new pipework | Strength test, tightness test, then purge |
| Pipework extended, for example new kitchen appliances | Strength test on the new section, tightness test, then purge |
| Pipework altered or repaired | Tightness test, purge where air has got in |
| Gas turned back on to an empty or capped off unit | Tightness test before the supply is restored, then purge |
| Smell of gas or a suspected leak | Tightness test once the area is safe |
| Pipework taken out of use | Purge out, then cap off |
A commercial kitchen refit is the most common case. New ranges, fryers or combi ovens often mean new pipework, and a kitchen cannot have its CP42 until the pipework feeding it has passed.
What the engineer does
A strength test is for new or extended pipework. The engineer isolates it and raises the pressure above the working pressure for a set time, to prove the joints and fittings can take it.
A tightness test proves the installation does not leak at its working pressure. The engineer first checks the isolating valve is not letting gas by, lets the pressure settle, then watches it over a set period. How much loss is allowed depends on the size of the installation and the rooms the pipework runs through. Calculating that is part of the test, which is why the pipework volume is worked out before the gauge goes on.
A purge replaces what is in the pipes. Bringing pipework into use, the air inside is pushed out with gas, through a purge point vented safely, until a gas detector confirms the pipes hold gas and nothing else. Taking pipework out of use, the gas is pushed out with air or nitrogen. Larger or higher pressure systems are usually purged with nitrogen, under a written procedure.
Plan for the gas to be off while this happens. In a restaurant or a hotel kitchen, that usually means booking it outside service hours.
What the CP16 should show
- The address and the part of the installation tested
- The pipework volume and how it was worked out
- The strength test pressure and duration, where one was needed
- The tightness test pressure, duration and result
- How the pipework was purged, and the final gas reading
- The engineer’s name and Gas Safe registration number
Keep it with the CP17 or CP42 for the same installation. An insurer, a landlord or an incoming tenant may ask to see both.
Who can do it
Testing and purging commercial pipework is its own qualification. An engineer registered for domestic gas only is not qualified for it. Before booking, check the engineer’s Gas Safe ID card lists commercial testing and purging, at the size of installation you have.
Testing and purging in London
Neos Engineering carries out commercial gas testing and purging, with a CP16, across London. For pipework under 1m³ the price is £1,500 + VAT (£1,800 inc VAT), plus hire of the purging equipment. Larger installations need a site survey first, then are charged at our commercial hourly rates. Annual checks are on our commercial gas safety page, and pipework alterations on our commercial plumbing page. For who must arrange the gas work in a shared building, see who is responsible for gas safety in a commercial building.
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