In the UK the most common method of determining that a gas membrane does not contain any defects is by carrying out a visual inspection. In many, and perhaps the majority, of cases no inspection or testing at all is carried out. In some types of development/construction it is difficult/impracticable to carry out integrity tests and in these situations a more onerous verification process may need to be adopted
Ciria C735 states that tests on welded seams and tape joints should always be carried out (where practical) when gas membranes are used for gas protection in buildings.
Integrity tests on seams and details i.e. pipe penetrations, are carried out in the UK, Europe and the USA, generally based upon ASTM standards. Tests are carried out routinely at fabrication and on site.
SEAM/JOINT & DETAIL TESTING
The principle techniques as defined in Ciria C735 are:
• conductive geomembrane spark test (ASTM D7240-06:2011)
• air lance test (ASTM D4437)
• vacuum box test (ASTM D4437)
• ultrasonic pulse echo testing (ASTM D4437)
• mechanical point stressing (ASTM D4437)
• standard practice for pressurized air channel evaluation of dual seamed geomembranes (ASTM D5820-95:2001) •
PVC dual track seamed geomembranes (D7177-05:2010) • spark test (D6365-99:2011).
In the UK, the test methods that are commonly used are:
• AIR LANCE TEST (ONLY TEST SUITABLE FOR WELDED AND TAPED SEAMS/JOINTS)
• pressurised air channel tests (suitable for Dual track welded seams only)
• spark tests (suitable for Extrusion welded seams only)
• mechanical point stressing/PICK TEST (only suitable for welded joints and should be used in hard to reach areas and in conjunction with one of the above tests)
Integrity tests to find small holes in membranes are more limited in number/type and are generally not well defined by published standards or derived from rigorous scientific testing and assessment. Three main types of testing are currently available in the UK:
It is worth noting that pinhole integrity testing is usually only required on higher risk sites and in all instances wet weather WILL affect the reliability of the test results (Ciria C735). Some companies are offering pick tests and tracer gas testing as a means of testing tape joints in the membrane, Ciria 735 recommends that air lancing is the only test that should be used to test these areas.
Written by Michael Corban, Co-Author of CIRIA C735 "Good practice on the testing and verification of protection systems for buildings against hazardous ground gases" 2014