Burst Testing Minimizing Variation
Burst testing is an excellent way to rapidly evaluate the ability of a package to withstand internal pressurization such as may occur during sterilization and/or transportation. Because of its speed and ease of use, it is often used as an in-process test.
Two versions of the test exist, F1140 Internal Pressurization Failure Resistance of Unrestrained Packages for Medical Applications and F2054 Burst Testing of Flexible Package Seals Using Internal Air Pressurization Within Restraining Plates. The two methods are very similar except that F2054 uses restraining plates to minimize the expansion of the package.
“For some combinations of materials, data from this test may have a very high standard deviation.”1 There are a number of strategies used to control variation.
Techniques to Minimize Variation
- The material used to produce the package must be the same. As the extensibility of the materials used to construct the package increases, the burst results will also increase.
- The rate of pressurization must be controlled and repeatable. The approach to pressurization, that is pressurizing at a constant flow rate or a flow rate that ramps up, must be consistent between tests. Note: different testing equipment manufacturers utilize differing approaches to flow rate.Fast pressurization rates can increase variability. On the other hand, if the pressurization rate is too slow, the package seals may begin to creep open skewing the burst test results.
- When testing packages that contain porous materials, variations in the porosity of the material will impact the effective pressurization rate. This introduces variability in the burst test results.With very porous materials or larger packages, it is possible to be unable to provide sufficient air volume to achieve rupture. The use of blocking agents to limit the porous area can allow these types of packages to be tested. Blocking agents include tape and labels as well as non-breathable coatings (such as WholeSeal marketed by DBI, Inc.). Care must be taken that the blocking agent is applied to a consistent area of the package and that it does not interfere with the seal.
- The package size and/or configuration must be consistent. As the pressure is distributed over a larger surface area, the burst value will decrease. In addition, changes in configuration can result in changes to the pressure distribution and affect the burst value.
- By using restraining plates as described in F2054, the expansion of the package is minimized. As a result, the pressure is more evenly distributed across the package seals. The gap dimension should be set to minimize the distortion of the package during inflation. In order to compare results, the gap dimension must remain constant. This approach has been shown to reduce variation as compared to unrestrained testing.
Variability is inherent to this test. When conducting interlaboratory testing or referee testing, results achieved through the use of F88 Seal Strength of Flexible Barrier Materials is the determinant factor.
1ASTM F2097-07 p.13