Steam Dryness Value for Saturated Steam Autoclave

Dear all,

If the steam dryness at the user point would be too low (lower than 0.90 - see EN 285), what would be the impact on the sterilization performance?

wet pack after the cycle, or also performance risk? Any workaround in case the steam is too wet?

Also, for metal loads, this limit is 0,95 (see EN 285), why is it a bit more strict for metal loads?


As far as I remember the EN 285 guidance has been revised and updated in the final draft stating that "all sterilizers should operate with a dryness value not less than 0,95 .

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EN285 clearly states dryness fraction of 0.95 and higher . if you have a value of .90 at the user point I would look at the feed water to your generation plant also do you have a blow down in place. what is the conductivity of your clean steam all these are critical . Also the method implied to carry out the test is critical if for example you use the wrong pilot tube size this can give you bad results.

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Hi Monepoc

The main effect of wet steam is that it will produce wet loads. Wet loads are bad news because contamination can be transferred from to the load via the packaging. The packaging (paper/cotton/linen etc) is considered as a filter against microbes to prevent re-contamination. The filter does not work if it is wet.
Wet steam can cause transfer of condensate from load items in a chamber to those items below.
Wet steam is also less efficient than dry saturated steam.
There is no work around for this. Your steam quality is essential for good performance of the sterilizer.

The limit for Non-metal loads was dropped in 2015 version. It would be very rare to have a system (sterilizer and steam service) that would process non-metal loads only so there is no point in having two limits. Metal loads require more energy transfer to heat them than non-metal. In heating, metal loads produce more condensate. EN285 is of course intended primarily for clinical sterilizers in a medical situation but is often used for Biomedical and Pharmaceutical use.