What Is the Smallest Hole Detectable in a Seal?
What is the smallest hole detectable in a seal with common measurement technologies?
This question is often asked, probably because the answer is not easy to find. Look to ISO 11607-1 2006 for guidance and at the end we find Annex B (informative); this annex contains a list of standardized test methods and procedures that may be used to demonstrate compliance with the requirements of this part of ISO 11607. A careful review of this listing reveals six ASTM standards designed to facilitate the detection of leaks in flexible packaging. If we ignore D3078 and F2096, which only apply to "gross leaks", there remain four standard test methods to consider. All these tests may be used for testing seals involving porous substrates such as Tyvek®.
The least sensitive method is described in ASTM F2338-09 "Standard Test Method for Non-destructive Detection of Leaks in Packages by Vacuum Decay Method"; this method was validated by detecting "channel defects created using a 125 μm wire".
Next is ASTM F1886: 1998/F1886M-09 "Standard Test Method for Determining Integrity of Seals for Flexible Packaging by Visual Inspection"; this method was validated by detecting channel defects with both 75 μm and 125 μm wires; however the standard's precision and bias statement shows that detection of 75 μm channels is somewhat unreliable. As detection accuracy can be affected by the inspector's visual acuity, visual aids may be used.
ASTM F2228:2002 "Standard Test Method for Non-Destructive Detection of Leaks in Medical Packaging Which Incorporates Porous Barrier Material by CO2 Tracer Gas Method" appears to be better as it used 100 μm calibrated channels in its precision and bias testing with a good rate of defect detection.
The most sensitive method for seal leak detection is ASTM F1929-12 "Standard Test Method for Detecting Seal Leaks in Porous Medical Packaging by Dye Penetration." Precision and bias checks show that when several laboratories tested seals with channels created by a 50 μm wire, the channels were detected 99 percent of the time. The standard states, "The 95% confidence interval is 97.7% to 99.1%", this test requires package destruction.
To answer the original question, I conclude that the smallest hole detectable in a seal with common measurement technologies is one with a diameter of 50 μm. Dye penetration testing achieves this when testing pouch and blister tray sealing with the advantage that it requires little equipment and achieves consistent, reliable detection.
Rolande Hall, FIMMM Pkg Prof