Hi Maureen
The settle plate is exposed for the period of the operation, up to a
maximum of 4 hours (based upon Orange Guide recommendations). If
the operation takes longer, say 6 hours - then you expose a plate for the
first four hours, change the plate and continue to expose a second plate
for a further 2 hours. If the operation is less than 4 hours, say 2
hours, exposure of the plates is for 2 hours and the specification
amended accordingly. However for Grade A cabinet the limit is <1
cfu/4 hours anyway - so you would stay with that limit, as this limit
generally reflects the condition of a very clean environment with any
contamination warranting some sort of review dependent upon your
procedures.
Whether settle plates should be used - this should be considered as part
of your environmental monitoring policy for that environment, typically a
HACCP review or something similar would be carried out initially to
define your monitoring regime and this would consider the need for settle
plates within that environment. However, you would need a very good
rationale not to include settle plates especially for the EU market.
Hope this helps.
Treena
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