The UK gas industry has officially entered a new era of safety and precision. In March 2026, the Institution of Gas Engineers and Managers (IGEM) released IGEM/UP/1B Edition 4 (Communication 1903). Replacing the long-standing Edition 3, this update introduces the most significant changes to tightness testing and purging procedures in over a decade.
If you are a Gas Safe registered engineer, understanding these changes isn’t just about best practice, it’s about staying compliant. Here is everything you need to know about the regulatory shift and how it affects your daily work.
The Transition Window: March to September 2026
The first thing to know is that you have a “grace period” to get up to speed. While Edition 4 was published in March 2026, there is a 6-month transition period ending on September 30, 2026.
Concurrent Standards: During this window, both Edition 3 and Edition 4 are technically valid.
Gas Safe Compliance: The Gas Safe Register has confirmed they will not “defect” businesses for using the older Edition 3 procedures during this time. However, by October 1, 2026, full compliance with Edition 4 is mandatory.
The Big Change: Installation Volume (IV) Over Meter Size
Historically, engineers determined permissible pressure drops based on the size of the gas meter (e.g., U6 or G4). Edition 4 scraps this approach for Natural Gas.
To align Natural Gas testing with the more rigorous standards already used for LPG, permissible limits are now dictated by the Installation Volume (IV).
The New Workflow: If you notice any “perceptible movement” on your gauge, you can no longer simply check a meter-size table. You must now calculate the specific volume of the system (or section) being tested.
Automatic Pass Thresholds: To save time on smaller systems, if the drop is below a certain threshold (e.g., less than 1 mbar for Natural Gas), you may not need to calculate the IV, as it qualifies as an automatic pass.
Pipework Integrity: No Room for Error
One of the most vital safety updates in Edition 4 is the emphasis on pipework integrity. The standard now aims to ensure that even a “permissible” leak isn’t hidden within the building’s infrastructure.
Isolate and Repeat: If a pressure drop is detected but falls within the “permissible limits” for the total system, you are now required to isolate all appliances and repeat the test.
Zero Tolerance: The goal is to prove the pipework itself is 100% sound. For the pipework-only portion of the test, there must be no perceptible movement on the gauge. If it moves, the test is an immediate fail.
Simplified Purging Procedures
Purging has been streamlined to remove the ambiguity surrounding different pipe diameters and meter types.
The Universal Formula: A single calculation now applies across all installations to determine the Purge Volume (PV):
PV = 1.5 x IV
By making the calculation strictly volume-based, the industry ensures a consistent and safer purge every time, regardless of the meter’s badged capacity.
New Permissible Limit Benchmarks
The new tables categorise drops based on the total cubic meters (m3) of the installation. Below are key examples of the new limits:
| Fuel type | Installation volue (IV) | Max pressure drop |
| Natural gas | <0.005 m3 | 8 mbar |
| >0.015-<0.035 m3 | 1 mbar | |
| LPG | <0.0025 m3 | 2 mbar |
| >0.01 m3 | No perceptible movement |
Crucial Reminder: For any system consisting of pipework only (or where only brand-new appliances are being connected), the standard remains “no perceptible movement” allowed.
Stay Ahead of the Curve
The shift to IGEM/UP/1B Edition 4 represents a higher standard of accuracy for the gas industry. While the transition period allows for some breathing room, the move to volume based testing requires new skills and a more methodical approach to on-site calculations.
