Posted 09/08/2006 09:58:39  |  By Terry McAuley | independent sterilisation consultant | Australia

I have some comments on performance testing of S type cycles.

If a steriliser actually uses a vacuum system to achieve air removal - but only claims their machine is suitable for processing packaged items (ie a Type S with a limited claim) or packaged items and Hollow B devices, should this type of machine have to have an air removal and steam penetration test done on it?

My opinion is yes - because the air removal system (ie vacuum pump) is a critical aspect of the safe and effective operation of that machine to process packaged and Hollow B items. For example, most information I read now on Downward Displacement air removal type sterilisers indicates they are only suitable for processing unwrapped solid items. If manufacturers of sterilisers with Type S cycles are relying on the vacuum to remove air from the package or Hollow B device - then surely there should be a test to establish it (the vacuum pump)is operating effectively - just as we would if the machine is being used to process hollow A items.

I know about the performance tests described in EN 867-5 but this standard does not describe a device to performance test a cycle that claims only the ability to process Hollow B and packaged items. The issue isn’t about sterilisers that claim ability to sterilise Hollow A items. It is very clear how we should performance test these machines - ie Hollow A equivalent PCD or calibrated BD pack according to EN 867-5 - although what hasnt been clarified is whether a Hollow A PCD or the porous load PCD should be used - particularly if the machine/cycle is used to process both types of items!!

The problem we have in Australia and New Zealand is there are manufacturer's products from all over the world imported into our countries - and a lot of stuff from the US/Canada. The US small (and some of the larger) steam sterilisers often use the Joselyn principle for air removal - and it is known that it is not the best way to remove air from lumens!

End users believe that the salespeople of sterilisers are telling them the truth when they say the machine will sterilise their types of items - when clearly in many cases this is not correct! Until we mandate that sterilisers must have independent validation of label claims, this problem will continue and people will purchase these cheaper and so called "simpler" machines with S cycles - because there is no clear requirement to performance test them.

Because this cycle type (S) is recognised in EN/ISO 13060 we on the Australian standards committee incorporated them into our documents AS/NZS 4815 and soon into AS/NZS 4187. However, we have developed requirements for the performance testing (ie an air removal and steam penetration test) of Type S cycles claiming air removal and steam penetration capability from either Hollow B (or Hollow A) devices put this into the Standard - even though, to my knowledge, such a test is not yet commercially available.

In summary, I believe that urgent review of EN 13060 is necessary to clarify the issues I have raised above and to ensure that small steam sterilisers, whether they are used in hospitals, primary care and office based practices meet the same performance and safety requirements when reprocessing reusable medical devices.

I would be happy to be involved in such a review.

Ms Terry McAuley
Sterilisation and Infection Control Consultant
+61 438109692

Posted 13/09/2006 20:00:00  |  By Mathieu Giang | AFNOR

Commenting template CEN/TC 102 - Document: prEN 13060 [PDF file]

Posted 17/05/2008 14:02:52  |  By CEN/TC 204/WG 11

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As an answer to request regarding "Formalin tablets as a source of sterilant":

This subject was discussed by CEN/TC 204/WG 11 at its meeting in Vienna 2006-05-04 and the following statement was agreed.

The purpose of EN 14180 was to create a standard that could guarantee a formaldehyde sterilization process that was reproducible within certain limits and where all essential parameters for sterilization were known and could be derived by physical calculations. This included the most important variable i.e. the concentration of formaldehyde in the gaseous steam and formaldehyde mixture being defined as sterilant.
To secure a reproducible and uniform gas mixture in the chamber it is necessary to proceed from a liquid formalin solution with known concentrations of both formaldehyde and water and further to vaporize this solution into a steam and formaldehyde gas mixture, consequently with known concentrations of both formaldehyde and steam.
Only by using this method you could get a known result in the chamber and a reproducible gas concentration that also is possible to derive from physical calculations. The essential requirements of EN 14180 in clause 5.1.3, 5.2.2, 5.2.3 and 5.2.4 could not be met otherwise.
Therefore means to obtain sterilant by vaporization of a solution is defined in 3:20 and the cycle variables, including concentration, and parameters intended are defined in 3.10 and 3.9 respectively. Heating of paraformaldehyde and using it alone as sterilant could if air is evacuated result in a known gas concentration.
However, then the gas penetration is only managed by diffusion of gas instead of thermodynamics and the necessary humidity to ensure the killing of spores is missing. Such a method could not be classified as sterilization but only disinfection as being well established in scientific publications.
Further, if mixing this vaporized formaldehyde with steam to become a sterilant the result will not be a uniform and predictable sterilant. In this case you will obtain the necessary humidity but the physical thermodynamics will force as much steam into the chamber as the actual load weight requires to be heated to sterilization temperature. As this amount of steam will vary with loads you could not secure predictable steam versus formaldehyde ratios in the chamber and thus no reproducible concentrations of the sterilant.

With best regards,
CEN/TC 204/WG 11