Some industrial processes are denominated as "special" by EN 29000 series of European standards, if the verification or checking action destroy the involved tested product or service.
Sterilization is a "special" process because sterility checking destroys the sterile status of a product (the sterile item package has to be violated) and sometimes even the product itself.
This situation conducted to "parametric release" - the product release to the market based on process documents proving the accordance with parameters approved in the validation step.
An important scientific discovery was that the inactivation of microorganisms (sterilization) by any physical or chemical mean (heat, toxic gas, radiation) is governed by an exponential low.
There is, inevitable, a probability a microorganism to survive quite indifferent the sterilization conditions are (the temperature level, the gas concentration or contact time, the radiation dose, etc).
From hear follow 2 consequences:
- The word "sterile" that common sense interprets in terms of "yes" or "no" has to be understood in terms of probability. This concept is known as "sterility assurance level" or SAL.
SAL is a concept connected with risk idea. For instance a SAL = 10-6 mean that the sterility of 1 product from 1 000 000 products stamped "sterile", can not be guaranteed.
The validation of all industrial sterilization processes begins with establishing the desired SAL.
- The results of a sterilization process essentially depend on bioburden existent on medical device before sterilization. It comes from raw materials, packages, workers and manufacturing conditions.
To benefit of the great feasibility of irradiation sterilization process, the bioburden level of different manufacturing lots, have not to be over the level established at the validation lot. This is an important responsibility of the manufacturer.