Numerical prediction of the chemical indicator response used in steam sterilisers

Steam sterilisation is a commonly used method in the sterilisation of surgical instruments. To ensure the sterility of the sterilised goods an evaluation of the sterilisation process is required. This might be achieved either through physical measurements or indicators. Optimal sterilisation results are achieved by removing the air from the sterilisation chamber. In this paper a new computational fluid dynamics (CFD) based approach is presented, which allows to calculate the steam distribution within a sterilisation chamber with focusing on hollow loads. Additional measurements were performed using a self-developed measurement chamber to validate the CFD model. A modified process challenge device (PCD) with different tube lengths in combination with a chemical indicator (CI) was tested, to identify the volumetric influence of the lumen on the resulting air-steam mixture therein. A numerically efficient model was developed to determine a steam volume fraction threshold leading to a response of the CI. This study aims to predict the volumetric amount of steam which is necessary in order to pass a PCD test fitted with a CI. Both the CFD model and the measurements showed that often an insufficient steam penetration is indicated by PCDs which can lead to an insufficient sterilisation of hollow loads.