Vacuum decay is more sensitive than pressure decay due to the volume and pressure that is being measured.
-A Pressure decay test in which the outside of the package is pressurized will measure the pressure change of air flowing into the package from the high pressure environment, which has several times the standard volume of air than the same space placed under vacuum.
-A leak of a specific size can only allow a certain molecular flow of air through the leak.
-A Vacuum decay will be dramatically more sensitive as it measures the change in vacuum level.
-A leak of a specific size will pass a similar molecular flow through the leak, and that mass of air will have a greater impact on the vacuum measurement space when compared to the same space under a pressure decay environment.
-Thus vacuum decay will always be more sensitive.
Pressure decay also introduces the possibility of forcing environmental contaminants through a defect into the samples, violating a non-destructive test
