Quantitative assessment of the standard method for measuring steam composition in surface sterilisation

Steam composition, defined as the fraction of non-condensable gases (NCGs) in the steam, is an essential parameter to ensure the efficacy and reliability of the steam sterilisation process. Standard EN 285:2015 + A1:2021 defines an operative method for measuring NCG fraction (NCG%) in the steriliser steam pipes, but lacks specifications about the process profile, timing and volume of condensate, and environmental conditions. This study aimed to quantify the effects of this lack of specifications on NCG% measured values to enable a more effective and informative testing procedure. Sterilisation processes, with different profiles and load amounts, were run in a medium-sized steam steriliser. NCGs and steam condensate volumes were measured every 30 s using the standard method, and NCG% values were calculated at different time points and condensate volumes. NCG% variations associated with environmental temperature and pressure were theoretically estimated. NCG% values and test outcomes showed dependence on the process profile, load, condensate collection timing and volume. Environmental conditions had a non-negligible impact on measurements. Overall, NCG measurement variability impacted standard method reliability to qualify the steriliser and to estimate steam composition in the steriliser chamber. Real-time quantitative monitoring of steam composition during every production process is advocated to improve steam sterilisation efficacy and quality.