The main changes to IGEM/UP/1B Edition 4 focus on how engineers carry out and assess tightness testing and purging on small domestic and light commercial gas installations. The new edition was published in March 2026 and becomes mandatory from 1 October 2026, replacing Edition 3.
Here are the key changes explained simply:
Installation Volume (IV) now replaces meter size
Previously, permissible pressure drops during a tightness test were based mainly on the gas meter size (for example U6 or U16).
Edition 4 changes this completely. The allowable pressure drop is now based on the Installation Volume (IV) of the pipework system instead.
This means engineers now need to:
- Calculate the total internal volume of the installation pipework
- Use the new IV tables to determine permissible pressure loss
- Record IV calculations during testing and purging procedures
This is one of the biggest procedural changes because it creates a more accurate reflection of the actual gas installation rather than relying purely on meter capacity.
Clear definition of “Perceptible Movement”
Edition 3 referred to “perceptible movement” on gauges, but Edition 4 now gives a precise definition.
The standard now states:
- 0.25 mbar movement on a water gauge
- 0.2 mbar movement on a high-resolution electronic gauge
Any movement beyond these values is now treated as a fail during certain testing stages.
This removes interpretation differences between engineers and creates a more standardised testing method.
Mandatory pipework-only retest
Another major update is the introduction of a mandatory pipework-only retest when appliances are connected to the installation.
Under the new procedure:
- The full installation is tested
- If appliances are connected, a secondary test on the pipework alone must also be completed
- Any perceptible movement during this retest is classed as a failure
This aims to improve leak identification and reduce ambiguity around appliance-related pressure changes.
New standardised purge volume formula
Purging calculations have also changed significantly.
Edition 4 introduces a standard formula:
PV = 1.5 × IV
(Purge Volume = 1.5 multiplied by Installation Volume)
Previously, purge calculations varied depending on pipe diameter and meter type. The new approach simplifies the process and standardises purging calculations across installations.
Caravan and Leisure Accommodation Vehicles now included
Edition 4 now specifically includes:
- Caravans
- Leisure Accommodation Vehicles (LAVs)
within the scope of the standard.
This broadens the applicability of UP/1B and gives clearer guidance for engineers working in those sectors.
Hydrogen blend clarification
The updated standard also confirms that Natural Gas containing up to 20% hydrogen blend is within scope.
This reflects the industry’s preparation for future low-carbon gas networks and hydrogen blending projects.
Scope and limits remain broadly similar
The standard still applies to:
- Installations up to 35 mm nominal bore
- Meter capacities up to 16 m³/h
- Domestic and small commercial properties
- Operating pressures up to:
- 21 mbar NG/LPG-Air
- 37 mbar LPG
- 2 bar MOP upstream limits
Why these changes matter
The new Edition 4 is designed to:
- Improve consistency across engineers
- Make tightness testing more accurate
- Reduce subjective interpretation
- Better reflect modern pipework systems
- Improve safety and traceability
- Prepare the industry for future gas network changes including hydrogen blending
For engineers, the biggest practical adjustment will be becoming confident with:
- Installation Volume calculations
- New permissible drop tables
- Revised purge calculations
- Updated testing sequences
