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Correct loading of your steriliser

This month we are going to focus on the importance of loading our steriliser correctly. Whether you are using an N, S or B class autoclave it is incredibly important to ensure that the chamber is loaded correctly using the manufacturers instructions as guidance.

Overloading the steriliser

Every autoclave will have a maximum weight capacity that the chamber can accommodate. The weight will vary depending on the size of the chamber and the individual manufacturer specifications. When the perforated dental trays are used its important that instruments are laide out next to each other and do not overlap.

If instruments are overlapping or touching this may inhibit the autoclaves ability to sterilise the instruments correctly as there will be areas that the steam will not be able to reach fully. Any instrument placed on the tray should have a small amount of space between the next to all the steam to fully reach all acceptable surface area’s.

Overloading of the autoclave chamber may also result in a couple of other issues. Firstly the increased load may result in a prolonged warm up time to reach the desired sterilisation temperature, resulting in the overall cycle time being increased. Secondly, if using a vacuum autoclave, the increased load may result in pouches coming out of the unit wet.

Wet Wicking

If pouches are overloaded in the vacuum autoclave this can be a course of a phenomenon called ‘Wicking’. The definition of Wicking is ‘acting to move moisture by capillary action from the inside to the surface’

Wicking can occur from ‘Wet Pack’ pouches which have moisture on or in the pack when removed from the steriliser. Moisture may be evident as visible dampness, droplets, puddled water or crinkled pouches on or within a pack. Wicking allows microorganisms to enter through the packaging, resulting in recontamination of sterile instruments. Wet packs can also cause instrument corrosion.

Its important that if you witness ‘Wet Pack’ pouches when unloading the autoclave that you do not touch them and allow them to dry fully before handling.

Ways to avoid ‘Wet Packs’

There are several things that we can do to try to avoid unloading any wet packs from the autoclave.

· Don’t overlap your pouches – these should be placed side by side on the perforated tray which not only helps with the sterilisation but also the drying.

· Follow the correct tray loading of the autoclave. Generally you should allow a full dental tray gap between each pouched load to help facilitate adequate drying of the pouches. Basic rule is if your autoclave takes 5 trays of unwrapped instruments then it will take 3 trays of wrapped instruments.

Allow your pouches to breath

When loading your pouches its important to overload them as they need to breath in the autoclave. Its important that you select the correct size pouch for the number of instruments that you require, without them being stacked. Once the instruments have been placed you should be able to place a fingers width down each side of the instruments touching the pouch outer edge. There should also be a figures width at the top of the pouch once the seal has been stuck down.

Once the pouches are placed in the steriliser, steam will enter the paper side and fill the pouch, making it inflate slightly. By ensuring that it is correctly loaded this will minimise the risk of instruments piecing the paper once they deflate and contract.

Seavey R. Packaging systems for sterilization. Nursing Lesson Plan 618. IAHCSMM website. Published November/December 2016. Accessed December 27, 2019.


Everyone is extremely busy and we often work on auto pilot, especially when performing the same routines day in day out. Just try to remember that correct loading of our autoclaves can not only help with the sterility of our instruments but can also improve efficiency through correct working durations of our equipment.

We have created a Testing & Validation Guidance Handbook to support the wider Dental team who are looking for answers to questions such as these. The handbook has been developed to provide help and support with all things around the

decontamination process including what to do if tests fail.

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