Based on the PPM you listed (if indeed this is accurate), I would expect a
D-value anywhere from 7 to 14 minutes using the Steris Cycle Development Guide,
with an average D-value around 11 minutes. This range in D-values has to
do with the percent saturation of hydrogen peroxide, with the lower D-value
having a higher percent gram saturation (closer to the point of condensation).
In other words, at 700 PPM and 65% gram saturation one would expect a
D-value of approximately 14 minutes, and at 95% gram saturation one would expect a
D-value of approximately 7 minutes. This is why temperature and humidity are
so important in this process. Given your BI log of approximately 6.28 log,
your cycle should be GREATER than approximately 44 minutes (7 minutes/log
reduction x 6.28 log). Truthfully, you may see positives even at 44 minutes.
So to answer your question, I do not find it at all surprising that you did
not see total kill at 35 minutes.
On a side note, my firm now fabricates condensation sensor technology
coupled with or without high concentration hydrogen peroxide monitoring to aid in
performing D-values, cycle development qualification, etc. Please email me
directly if interested and I will send you the appropriate information. As you
can imagine, demand has been very strong.
Yours in Service,
ARDIEN CONSULTING SERVICES
The Barrier Isolation Technology Specialists
Serving the Pharmaceutical Industry Since 1994
Rick Nieskes - Barrier Isolator Consultant
825 Lynnewood Drive
Waukesha, Wisconsin 53188
Email: [log in to unmask]
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