Pressure Decay Method


Pressure Decay Method (PDM) is a non-destructive Container Closure Integrity (CCI) testing practice applicable to most pharmaceutical package systems.
PDM is usually the preferred approach when dealing with oil-based products (high viscosity or density).

CCI testing is performed while the package itself is held within an hermetically sealed test chamber.
In the presence of failure in the package closure integrity (leakage), as a consequence of the application of pressure within the test chamber and hence of a differential pressure between the inside and the outside of the package, the air moves from the high pressure zone (outside the package) to the low pressure zone (within the package), causing a progressive pressure drop (that is a pressure decay) outside the package.
A pressure decay greater than a given threshold at end of the testing phase, points out a leakage. 
 
Once the test chamber is loaded with the package to be tested and hermetically closed, the PDM process comprises the following phases:
  • Pressurizing: the period of pressure setting within the test chamber;
  • Stabilization: the time necessary to get a homogeneous pressure distribution within the test chamber;
  • Testing: the time frame in which the pressure level is monitored by means of a dedicated transducer; two measurements are taken respectively at the beginning (1st reading) and at the end (2nd reading) of this phase.

Following the testing phase the PDM decision-making is performed by means of comparing the pressure decay DELTA “Δ” (Δ = 1st - 2nd reading) to a predetermined threshold THR:

if Δ ≤ THR the PFS is classified as conforming (no detectable leakages) 
if Δ > THR the PFS is classified as defective (a micro leakage is detected)
In case that a preset minimum level of pressure (M_LEV) is not reached at 1st reading time, the package is classified as defective as well (a large leakage is detected)