Industry Standard Update 133 (Edition 2)

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: 15th April 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(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the new version for a period of 6 months, until 30th September 2026, at which point IGEM/UP/1B Edition 3 will be withdrawn.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 conversant with the new procedure during inspections and will provide guidance where necessary.

We have received feedback from industry that the original ISU 133, published on 25th March 2026, has caused some confusion and misinterpretation. Therefore, we have worked with industry to produce this second edition of the ISU, which supersedes the original.

General

The main changes in IGEM/UP/1B Edition 4 are that permissible pressure drops on a tightness test are determined by the Installation Volume (IV) rather than meter size alone, and that where there is any perceptible movement of the gauge this is not attributable to gas installation pipework. 

Tightness testing procedure

The procedure for carrying out tightness testing remains broadly unchanged. However, the method for assessing results and the required follow-on actions have been revised.

Where a tightness test is undertaken, if there is no perceptible movement, the installation can be considered gas tight. If there is any perceptible movement of the gauge, the observed pressure drop shall be determined whether it is within permissible limits. These limits are defined by gas type, and Installation Volume (IV). 

Therefore, the IV of the installation (or part of being tested) shall be calculated, and compared with the relevant table for the fuel gas type (Permissible Limits Table below). Where the drop is outside of permissible limits, the escape must be traced and repaired, or the installation disconnected from the gas supply and made safe.

Where the drop in pressure is found to be within permissible limits, it must then be determined that the drop in pressure is not attributable to the installation pipework. 

To do this, all appliances shall be isolated from the gas supply, and the test repeated on pipework only. There can be no perceptible movement of the gauge during this test for it to be deemed a pass. Where it is not reasonably practicable to isolate appliances, the test shall be carried out with appliances connected. Where perceptible movement is recorded, then the test shall be deemed a fail and the escape traced and repaired, or the installation disconnected from the gas supply and made safe.

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 lead detection fluid (LDF). There must be no smell of gas.

Overview of updated test procedures

The bullet points below state 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) or appropriate valve
  • Connect gauge and carry out let-by test at 7-10 mbar for 1 minute
  • If let-by passes, raise the pressure to the relevant tightness test pressure for the fuel gas 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 (IV) of the installation must be calculated 
  • Compare the drop on the gauge with the IV of the system on the corresponding Permissible Limits table, to ensure the drop is within permissible limits
  • Where the drop is within the permissible limits, then all appliances shall be isolated and the test repeated on pipework only (this is to ensure that any drop in pressure is not attributable to the pipework system)
  • There can be no perceptible movement when testing pipework only, or the test shall be deemed a failure, and the escape traced and repaired or the system made safe
  • Where the drop is outside of the permissible limits, then the escape must be traced and repaired, or the system made safe
  • Where it is not practicable/possible to isolate an appliance, 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. There must be no smell of gas.

 

Permissible limits

The new permissible limits are as follows:

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

 

Perceptible Gauge movement

A movement of 0.25 mbar or less on a fluid (water) gauge is considered to be “not perceptible”. Therefore, if the gauge is seen to move, it can be inferred that the pressure within the installation has altered by more than 0.25 mbar. Where an electronic gauge is used, the pass criteria of “no perceptible movement” is considered to be a maximum of 0.25 mbar, except for those gauges that read to one decimal place, where “no perceptible movement” is considered a maximum of 0.2 mbar.

Purging

The procedure for carrying out purging operations remains unchanged. However, the method for determining the purge volume has been revised. 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. 

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:

www.igem.org.uk/resource/igem-up-1b-edition-4-tightness-testing-and-direct-purging-of-small-liquefied-petroleum-gas-air-ng-and-lpg-installations.html 

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).