Industry Standard Update 133

IGEM/UP/1B Edition 4 Tightness testing and direct purging of small Liquefied Petroleum Gas/Air, Natural Gas and Liquefied Petroleum Gas installations (1)

Date issued: 25 March 2026

This Industry Standard Update provides an overview of the key areas of change arising from the revision of IGEM/UP/1B Edition 3 Tightness testing and direct purging of small Liquefied Petroleum Gas/Air, Natural Gas and Liquefied Petroleum Gas installations (with Amendments October 2012) (2).

Introduction

During March 2026, IGEM published an update to IGEM/UP/1B Edition 3 Tightness testing and direct purging of small Liquefied Petroleum Gas/Air, Natural Gas and Liquefied Petroleum Gas installations (with Amendments October 2012)(2) (Communication 1759).

While IGEM/UP/1B Edition 4 Tightness testing and direct purging of small Liquefied Petroleum Gas/Air, Natural Gas and Liquefied Petroleum Gas installations(1) (Communication 1903) comes into effect immediately, it is understood that it will take time for all Gas Safe registered businesses to train and implement the updated procedure. 

Accordingly, the existing standard will run alongside the new version for a period of six months, until 30 September 2026, at which point IGEM/UP/1B Edition 3 will be withdrawn. During this period, Gas Safe Register has agreed not to defect any business that is not fully conversed with the new procedure during inspections and will provide guidance where necessary.

General

The main changes in IGEM/UP/1B Edition 4 are a shift on permissible limits being dictated by the meter size, and confirmation that any perceptible movement is not attributable to gas installation pipework. In the new procedure, the permissible limits on a tightness test are now decided by the Installation Volume (IV) of the installation (or the part of the system being tested). This change now aligns with the existing procedure for LPG installations. 

So, where there is perceptible movement on the gauge during a tightness test, the IV of the installation will need calculated and compared to the relevant table to ensure the drop is within permissible limits. Where the drop on the gauge is less than the smallest permissible limit (0.5 mbar for LPG/Air, 1 mbar for Natural Gas, and no perceptible movement for LPG), then the IV will not need to be calculated as it will automatically fall within permissible limits. 

However, where there is any perceptible movement of the gauge during a test, you must now confirm that this movement is not attributable to the pipework installation. 

To confirm this, where perceptible movement is detected during the test, once the drop in pressure is confirmed to be within permissible limits, all appliances must be isolated and the test repeated to confirm that the drop is not attributable to the pipework. 

If, in some occurrences, where it is not practicable or possible to isolate an appliance, then no perceptible movement would need to be applied, or consideration may be given for the installation of an appropriate isolation valve. If perceptible movement on the gauge persists after the appliances are isolated, then the test would be deemed as a fail and the installation would need to be made safe or repaired and re-tested.

On completion of a satisfactory tightness test, the appliances should be re-introduced to the installation and all disturbed joints, along with any installation pipework between an appliance and an isolation valve serving it, will need to be tested with leak detection fluid (LDF).

Purging

The direct purging of installations in Section 6 has been amended. Where previously the size of the meter and diameter of the pipework could determine the purge volume (PV), the updated procedures state that the installation volume (IV) needs to be calculated and the formula of PV = 1.5 x IV is applied on all installations to determine the purge volume. The purge procedures remain unchanged.

Overview of updated test procedures

The following is a basic overview of updated test procedures:

  • Undertake visual inspection and make sure appliances are appropriately set up, ie, cooker lids in the upright position, permanent pilots extinguished.
  • Turn off Emergency Control Valve (ECV)/control valve.
  • Connect gauge and carry out let-by test at 7 mbar -10 mbar for 1 minute.
  • Adjust pressure to test pressure for fuel gas of system and carry out temperature stabilisation for 1 minute.
  • Adjust pressure where necessary and test for a further 2 minutes.
  • For systems with pipework only or where only new appliances are connected, there can be no perceptible movement of the gauge.
  • For systems containing existing appliances, if there is any perceptible movement on the gauge, the Installation Volume of the installation must be calculated. Where the movement on the gauge is less than the smallest permissible limit for the gas being tested, there is no need to calculate the IV as you know the drop is within the permissible limit.
  • Compare the drop on the gauge with the IV of the system on the corresponding table to ensure the drop is within permissible limits.
  • Where the drop is outside permissible limits, then the escape must be traced and repaired, or the system made safe.
  • Where the drop is within permissible limits, you then need to isolate all appliances and repeat the test. This is to ensure that any drop in pressure is not attributable to the pipework system.
  • There can be no perceptible movement on this test or the test shall be deemed a failure, and the escape traced and repaired or the system made safe.
  • Where it is not practicable/possible to isolate an appliance, or to test any pipework between the isolation valve and the appliance itself with LDF, then test is carried out with the appliance connected and the no perceptible movement criteria applied.
  • Once the tightness test is complete, remove the gauge, refit the test nipple, reintroduce the gas and test all disturbed joints with LDF, along with all installation pipework between any isolation valve and the appliance it serves.

 

Permissible limits

The new permissible limits are:

Fuel gas Installation Volume (IV) (m3) Maximum permissible pressure drop (mbar)
LPG/Air (Table 2) ≤0.025
>0.025 – ≤0.035		 1.5
0.5
Natural gas (Table 3) ≤0.005
>0.005 – ≤0.010
>0.010 – ≤0.015
>0.015 – ≤0.035		 8
4
2.5
1
LPG (Table 5) ≤0.0025
>0.0025 – ≤0.005
>0.005 – ≤0.01
>0.01 – ≤0.035		 2
1
0.5
No perceptible movement

 

Summary

This Industry Standard Update is an overview of the information contained in the amended standard. Gas Safe Registered engineers/businesses should be aware that they have a responsibility to ensure that they are fully apprised of all the requirements of the whole published standard and their practical application.

You can review and download the standard at here.

Bibliography

  • IGEM/UP/1B Edition 4 Tightness testing and direct purging of small Liquefied Petroleum Gas/Air, Natural Gas and Liquefied Petroleum Gas installations 
  • IGEM/UP/1B Edition 3 Tightness testing and direct purging of small Liquefied Petroleum Gas/Air, Natural Gas and Liquefied Petroleum Gas installations (with Amendments October 2012)