Verification of Gas Protection Measures

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As a natural progression from undertaking Hazardous Ground Gas Monitoring and Hazardous Ground Gas Risk Assessments, iD Geoenvironmental Limited have extended our capabilities to include the additional services detailed below, in order to offer a more complete service and assist our clients in meeting the updated requirements of current guidance, legislation, and recognised best practice surrounding the assessment of, and protection from Hazardous Ground Gases.

iD Geoenvironmental are pleased to be able to offer the following additional services to new and existing clients within the private, residential and commercial construction sectors:

  • Preparation of Hazardous Gas Protection Measures Verification Implementation Plan

  • Independent On-site Visual Inspection and Validation of Gas Protection Measures

  • Independent On-site Air-Lance Integrity Testing of Gas Membrane Installations 

  • Preparation of Independent Hazardous Gas Protection Measures Verification Reports

  • Consultancy Support and Regulatory Liaison Throughout the Installation and Verification Process.

To provide our clients with a smooth and robust verification process, and ultimately to satisfy Local Authority Regulators, Planners, and local Building Control or NHBC, all of the above services offered by iD Geoenvironmental are in full compliance with current guidance, and are specifically tailored to meet the requirements of the following key documents:


  • BS8576:2013 - Guidance on investigations for ground gas – Permanent gases and Volatile Organic Compounds (VOCs).

  • BS8485:2015 - Code of Practice for the design of protective measures for methane and carbon dioxide ground gases for new buildings.

  • CIRIA C665 (2007) - Assessing risks posed by hazardous ground gases to buildings.

  • CIRIA C735 (2014) - Good practice on the testing and verification of protection systems for buildings against hazardous gas.

Verification Implementation Plans
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Where hazardous gas monitoring and risk assessment has identified a site or development to be at risk from hazardous ground gas, with a designation of Characteristic Situation 2 or above, CIRIA C735 requires a Gas Protection Measures Verification Implementation Plan to be prepared.  


The purposes of this document are to set out the verification activities and the integrity testing (if any) appropriate to the site-specific risk assessment, the development itself and the particular design and specification of the gas protection system in accordance with BS8485:2015.


This document also enables the client and potential contractors installing the gas protection measures to agree the design and products to be used, and gain an appropriate understanding of the level of independent verification inspections and any associated integrity testing required for the development. 

iD Geoenvironmental’s site specific gas protection verification implementation plans are designed specifically to meet the requirements of the guidance and regulators, whilst providing a solid basis for an efficient and economical verification process.

Visual Inspection and Validation of Gas Protection Measures

As part of the validation process, a number of elements of the gas protection measures require on-site inspection during the construction program.


In addition to inspection of the gas membrane installations, ventilation elements of the gas protection system including sub-floor voids, airbricks, sleeper wall ventilation also require inspection and validation to confirm that they meet the necessary performance criteria outlined in the guidance.


In accordance with CIRIA C735, conflicts of interest in verification should be avoided. Verification should be carried out by an organisation independent of the gas membrane installation contractor or the developer/main contractor.

iD Geoenvironmental are not affiliated with any manufacturer or installer of gas protection measures, and as such are appointed as an independent verification consultant. Not only does this ensure our inspections and validation work meet the requirements of the guidance, but also serves to protect the interests of our clients against variations from design specifications, variations from implementation plans, sub-standard workmanship and bad practice. All inspections are documented, including photographic records and proforma certification provided for each unit.

Integrity Testing of Gas Membrane Installations

Whilst the concept of gas membrane installations being inspected and validated has been around for a number of years, it is recognised that the weak point has often been the quality and care of workmanship during the physical installation and joining of the gas protection membranes.


Whilst a gas-resistant membrane itself affords extremely low permeability to hazardous gases including methane and carbon dioxide, the quality and permeability of the joins between individual membrane sheets are a key factor in the overall effectiveness of any membrane installation.


Visual inspection alone is often insufficient to identify small leak pathways across membrane joints, with such leaks significantly reducing resistance to gas permeation across the system as a whole. To address this issue, the most recent updates to guidance on validation advocates the use of various methods of integrity testing to identify such leaks in joins between membrane components, service entries and punctures within the membrane itself. The most robust and practical method of integrity testing on site is widely accepted to be air lance testing of seams and joins.

iD Geoenvironmental are now able to offer our clients an independent air lance integrity testing service in order to validate the quality and effectiveness of gas membrane installations at the time of installation on site. Whether this is for a membrane installed by groundworkers with no previous experience, or installed by a professional and qualified installer, our air lance testing will confirm the suitability and effectiveness of the installation and allow validation before construction continues beyond the point of no return, and provide a proforma certification that gas protection measures installed for a given unit are acceptable.


iD Geoenvironmental’s specialist equipment and air lancing procedure has been designed specifically to conform to the requirements of ASTM D4437-08:2013, to enable our competent engineers to complete the air lance integrity testing in accordance with the requirements of CIRIA C735.

Gas Protection Measures Verification Reports

In line with the guidance requirements, the final aspect of the verification process is the preparation of a Gas Protection Measures Verification Report. This serves to collate all of the inspection and integrity testing records for all units on a given site into a single completion report, documenting elements that conform to the implementation plan and provide justification for elements that may vary from the original plan.

iD Geoenvironmental’s site specific Gas Protection Measures Verification Reports provide confirmation to the client, regulators and local authority that gas protection measures have been installed to a satisfactory standard, and in accordance with the requirements set out in the Gas Protection measures Validation Implementation Plan.


Our verification reports meet the requirements of all relevant guidance, to provide a robust verification document, enabling sign-off of any outstanding planning conditions associated with hazardous ground gas protection.

Consultancy Support and Regulatory Liaison

In addition to the above services, iD Geoenvironmental have the knowledge and expertise to provide advice and consultation throughout the duration of a gas protection measures project.


Whether this is advice on designs, choice of gas protection components, working practices, or amendments to the outlined plans, we are able to provide support to our clients every step of the way.


iD Geoenvironmental are keen to take up regulatory liaison on behalf of our clients at various stages throughout the project, to ensure that local authorities, building inspectors and warranty providers are up to date and satisfied with any proposed, on-going, and completed works, which iD Geoenvironmental consider is vital in ensuring a smooth, efficient and trouble-free verification process