Improving parametric load release with the Non-Condensing Gasses sensor
In steam sterilization for medical equipment
J.L. Coster (TU Delft - Mechanical Engineering)
J. Dankelman – Mentor (TU Delft - Mechanical Engineering)
P.D. Robertson – Mentor (TU Delft - Mechanical Engineering)
J.P.C.M. van Doornmalen – Mentor
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Abstract
Steam sterilization is widely used in healthcare and pharmaceutical settings to ensure the effective decontamination of instruments and materials. While pressure is often associated with sterilization processes, it is not a sterilization parameter itself; instead, steam composition plays a crucial role. This thesis investigates the use of a Non-Condensable Gases (NCG) sensor to actively measure steam composition, with the aim of improving the parametric load release process.
The sterilization conditions currently applied originate from research conducted in the 1960s and remain in use today. These conditions include a sterilization temperature between 134 °C and 137 °C, a sterilization time of at least three minutes, and limits on non-condensable gases of ≤5 % within the load and ≤0.1 % in the free space of the chamber. Additionally, the standard specifies a limit of 3.5 % VNCGs per 100 ml of condensate, based on historical measurements performed in steam supply lines rather than inside the sterilization chamber.
To evaluate the potential of direct chamber measurements, experiments were performed using a sterilizer equipped with an NCG sensor and a needle valve that allowed controlled air leakage into the chamber. Four sterilization programs were tested. Each program began with a reference cycle without leakage, followed by cycles in which leaks were introduced at different stages during the conditioning phase. Two additional cycles were conducted with a load inside the chamber to assess the influence of load presence on NCG levels. Furthermore, theoretical calculations were performed to estimate the percentage of NCG per 100 ml of condensate using dilution factor calculations.
In total, 37 sterilization cycles were conducted. The results were evaluated based on sterilization time, temperature, and the percentage of NCGs measured during the holding phase. Three main findings emerged: steam composition varied significantly between cycles, air leakage occurring after the final vacuum phase produced the highest NCG peaks, and sterilization cycles could pass based on time and temperature alone while still failing when steam composition was considered. Although all cycles met the required time and temperature criteria, 9 out of the 37 cycles failed due to excessive NCG levels in the chamber.
The results demonstrate that the use of an NCG sensor can significantly improve the parametric load release process by enabling real-time monitoring of steam composition inside the sterilization chamber. This capability helps identify cycles that would otherwise be incorrectly approved, supports corrective actions when necessary, and reduces unnecessary re-sterilization. As a result, the NCG sensor contributes to improved process reliability, time efficiency, and reduced equipment wear.