Integrity testing a gas membrane installation is a technique used in the overall validation or verification of a gas protection system. During the validation plan at design stage, the levels of integrity testing to be incorporated should be set out. This is dependent on a risk assessment based on the Complexity of design, Number of plots/buildings, Gas regime risk on site and the Competency of the installation workforce.
Integrity testing techniques can also be employed on waterproofing systems, including green and blue roofs, SUDS systems, lagoon liners and anaerobic digestion plant bund liners. The process offers an independent test of these systems to add more credence and layer of insurance to a systems installation in line with the design. This is normally broken down in the following way:
- Seam/Joint Testing – This involves testing a taped or welded joint between a gas membrane and any penetration sealing details
- Leak Detection – Or pinhole detection is used to scrutinise an installed gas membrane protection system. This is done by testing an in-situ gas membrane for minute holes
CIRIA C735 (2014) Good practice on the testing and verification of protection systems for buildings against hazardous ground gases, offers guidance for independent validation and on differing types of integrity testing options and the frequency of their use depending on site risk.
The principle techniques are:
- Conductive geomembrane spark test (ASTM D4787-13)
- Air lance test (ASTM D4437-08:2013)
- Vacuum box test (ASTM D4437-08:2013)
- Ultrasonic pulse echo testing (ASTM D4437-08:2013)
- Standard practice for pressurised air channel evaluation of dual seam geomembranes (ASTM D4437-08:2013)
- PVC dual track seamed geomembranes (D7177-05:2010)
- Spark test (D6365-99:2011)
The most commonly used test on site are:
- Air lance test – This test is the only test suitable for welded and taped seams/joints
- Pressurised air channel test – This test is only suitable for a dual track welded seam
- Spark test – This test is suitable for extrusion welding
- Mechanical point stress test – This test is only suitable for welded joints
Leak Detection/Pinhole Testing
The principle techniques are:
- Dielectric porosity test (ASTM D4787-08)
- Tracer gas test (no recognised standard)
- Smoke test (no recognised standard)
Leak detection testing is normally used on higher risk sites. On lesser risk sites integrity testing is concentrated in crucial areas e.g. seam/joints and penetration details.
As with all integrity testing, wet weather will affect the reliability of test results. However with a robust validation plan, encompassing the required level of integrity testing, BS8485 and CIRIA requirements are met.
The results of the integrity testing completed onsite are compiled into the full validation file as lines of evidence. The integrity testing is used to build up a complete picture of the scrutiny the gas membrane installation was put under for local authority approval in line with the validation plan.