Decontamination
may be needed for the worst case. However, if in practice the materials are sterilised separately, this may prompt two types of worst case loads. This is important because dissimilar materials of construction affect the rate of heating (for example, metal heats up faster as it is a heat conductor, and plastics slower because they are a heat insulators). Furthermore, some items simply may not allow steam to penetrate and are thus hard to heat (such as filters, certain valves, and small tubing). Operational loading: Even when a matrix has been appropriately qualified, it is important to mimic the load exactly when using the autoclave for routine operations. Autoclave should never be overloaded and there should be sufficient space between items to allow for steam to permeate around the package. Revalidation failures: When autoclaves
are requalified (a practice that is typically performed on an annual or six-monthly basis) failures can occur. A failure will prompt a review of the physical controls, addressing some of the factors described above. They may also be a requirement to re-examine the load and to reassess worst-case. This can lead to an adjustment of operating parameters or to a change to the load. With certain failures it may be prudent to consider the division of different material types and their placement, such as reducing the metal mass in the load and check whether linen items on the top rack and metal items on the bottom rack. Another area to consider is with the positioning of items.
Containers should be spaced about one inch
apart from each other. Stacking should not be performed unless the container manufacturer gives specific information on this process. It is also important to place containers beneath other items since they will often produce condensate. Revalidation failures can be manifest as a
failure to inactivate biological indicators. This can be due to inadequate air removal, which is more common than inadequate conditions of temperature and time. Issues can also arise due to changes to load patterns, in relation to the earlier discussion over how load patterns should be assessed (such as mass in comparison with individual item configuration).
Summary This article has examined some of the failure modes around autoclaves used for sterilisation as part of the decontamination function. Some of the reasons for failures discussed include: l Matrix approach for validation. l Wet loads. l Steam supply.
l Loading method. l Packaging. l Pre-heating. l Non-condensable gases. l Condensate formation.
Sometimes more than one factor is in play and, certainly, to make a thorough evaluation of sterilisation, reliance cannot be restricted to chemical or biological indicators and a complete understanding of hazards and physical operating parameters is required.
CSJ
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3. Sandle, T. (2015) Risk Considerations for Installation of a New Autoclave in a Pharmaceutical Manufacturing Facility, Journal of Validation Technology, 21(1): 2-9
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About the author
Dr. Tim Sandle is Head of QA Compliance at Bio Products Laboratory and a pharmaceutical microbiology consultant. In addition, Dr. Sandle is a visiting lecturer, specialising in sterility assurance and decontamination practices, at both the University of Manchester and University College London.
November 2024 I
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