Since the sterility of a product cannot be confirmed with a non-destructive test before its application in patients, special techniques of quality assurance are required. In addition to the visual inspection of failures such as punctures, tears etc. it is necessary to consider other possible factors that impair sterility during transport and storage. One factor is the microbial challenge as a result of environmental air flow through the porous component of packaging. Whereas the relevant physical parameters for sterilization are used to control sterilization processes, the relationship between flow of environmental air into the sterile barrier systems and the probability of loss of sterility is not introduced as a data-based approach for shelf life calculation. Such an approach seems to be obvious because porous packaging material can only maintain sterility if its filtration efficiency is sufficient and not overburdened by the airborne microbial challenge so that sterility is not compromised.
The compatibility of the capacity to retain the airborne micro-organisms and the airborne microbial challenge is calculated according to following formula in order to meet the maintenance of sterility at the sterility assurance level (SAL) of 1:1,000,000: