Assessment of the Inaccuracy Inherent in the Exponential Model of Sterilization
Rudolf Friedrich Bliema,b and Georg Werner Nowakb
Laboratorium für Betriebshygieneaand Universität für Bodenkulturb, Vienna (Austria)
For more than 70 years disinfection and sterilisation have been based on two mathematical models of cell inactivation, the exponential or first-order rate function, and the Arrhenius function, with its derivations F0 and A0. Both functions
have been inextricably linked to one another and both are based on conceptual errors resulting in systematic inaccuracies. In contrast to established practice, the inactivation of microorganisms does not follow the pattern of a first-order reaction rate function. The application of the first-order rate function is based on a limited phenomenological similarity and has no basis in theory. The inaccuracy of the model lies one to two orders of magnitude above the level of tolerance accepted for sterilization processes. The inherent inaccuracy in its application presents considerable potential for error in sterilization and disinfection processes, unless high safety factors are applied. Despite the inherent inaccuracy, its simple mathematical utility together with a very high margin of safety (Sterility Assurance Level 10-6) have established this model as the standardized basis for heat sterilization, and the model is now being adopted for disinfection processes.
This paper offers a reassessment of the model and its potential for error.
Key words Disinfection, mathematical models • Sterilization, mathematical models
