Decontamination


sulphide) should be removed before the steam leaves the boiler. Of these, air is the principal non-condensable gas that can impede steam sterilisation, and carbon dioxide and oxygen are important contributors to corrosion in boiler systems. When they are not, these modify the steam and prevent it from being pure water vapour and, instead, it exists as a mixture of steam and gas.


Non-condensable gases become an


unwanted contaminant that can prevent the steam from contacting the item (hence they function as heat insulators, reducing the transfer of heat).8


This is something that is


unlikely to be detected by thermometric studies or biological indicators, where quantities of gas accumulate in packaging and prevent steam penetration. Non-condensable gases can also affect reliability, either by causing corrosion or blocking extraction vents.9


To verify, the volume


of non-condensable gases should not exceed 3.5 ml for every 100 ml of displaced water (as per standard EN 285: 2015).10 Pre-heating phase: During the preheat


process (as an autoclave warms up) operational problems can range from poor steam penetration, superheat, and damage to packaging. This can arise when the autoclave doors have a different temperature than the chamber or walls; or where the jacket temperature is not uniform or lower than intended; or if an item being sterilised touches the wall of the autoclave. Superheated steam is a problem, since this means the steam has been heated beyond its saturation point and is therefore less microbicidal, compromising process efficacy and the achievement of sterility. Packaging materials: Packaging needs to be well designed and of sufficient porosity so that steam can pass through packaging. In addition,


packaging should be water repellent to provide a sterile “field.” Furthermore, the packaging material must not change significantly during sterilisation or release any substances that might interfere with the action of the steam. How the set was packaged is a related factor. It is important to consider if the wrapper is too large (this traps condensate inside the set), whether the package was taped too tightly (this traps condensate inside package), the size of peel pouches for load contents (such as too much metal mass in the pouch). Pre-packaged item control: Before using


wrapping material, both the packaging material and the items to be wrapped should be held at room temperature (20⁰C to 25⁰C) and at a relative humidity of 30% to 60% for a period of time to acclimatise. Failure to do so will affect the efficiency of the sterilisation process. Post-packaged item control: When packages


are removed from autoclaves, they should not be wet (as discussed above) or torn or punctured. Furthermore, the integrity of the package should remain suitable for the assigned expiry time (and all autoclaved items should have an expiry time since the integrity of the package, especially with the seal, will not last indefinitely). Pressure control: Given that autoclaves


destroy microorganisms by direct steam contact at the required temperature and pressure for a specified time, pressure control is important. Weak pressure control can cause variations in steam velocities. This often arises because maintenance of the pressure-regulating valves (PRV) in the system is not always dependable. PRVs can change the condition of the steam and, in theory, can dry the steam as it passes through the valve. Validation matrix determination: When qualifying an autoclave, it is unlikely every load


configuration can be validated. Often a worst case (or worst cases) is selected, based on evaluating a matrix of all the items and the different, intended load configurations.11


If


there is an error in the way the matrix has been developed, this can lead to a sterilisation failure. The process of developing a robust matrix


involves evaluating items for their challenge for being sterilised. This can relate to mass and the number of objects, but not always. For example, a length of tubing with a narrow bore can sometimes be more challenging to sterilise than a large metal bucket. Once worst-case loads have been selected, a matrix is developed to determine the loads to be qualified. The objective with the matrix is to identify anything relating to the load that can affect the distribution of the incoming steam or which can affect uniformity of temperature. The assessment should also consider anything that can take heat away from the chamber can affect temperature uniformity. The orientation of the equipment is also important, and this affects whether the item is capable of free draining. Where there is uncertainty about what constitutes worst case, some initial work can be undertaken thermometrically (heat penetration evaluation tests); this allows data to be collected about heat distribution, and this ‘hard to heat’ study is recommended. Account should be taken with liquid loads (for example, the viscosity of the liquid), since this can affect heat penetration. Shape is additionally important, especially where there is the potential for trapped air (and thus difficulties with air removal are created) or with condensate collection. A further factor is the type of material, such


as elastomeric (rubber-like) materials and stainless steel. If these types of materials are used in combination, then a balance of both


36 www.clinicalservicesjournal.com I November 2024


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