Hi

in pre vacuum steam sterilizers we test it with a daily test (bowie and dick test) and it is recomended that the pack of the test should be exposed to temperature 34 to 37 C with exposure time equal to 3.5 m ..
my question is why is the exposure time equel to 3.5 m and not more or less?

thank you
laila

Laila

The B&D (chemical) indicator changes its properties in a defind environment.
The environment in which air removal efficiency can be demonstrated was defind by the indicator manufacturer at the appropriate working temperature (134C). The exposure period is defined too and differs between manufacturers (3.2 to 4 min.)

miki

Hello!

As far as I know, the 3,5 minutes are derived from:

1. 3 minutes is the minimum holding time at 134°C for a steam sterilization process
2. EN 285 allows maximum 30 seconds of equilibration time to reach 134°C everywhere in the load

So, 3 minutes plus 30 seconds gives the test time. If anyone knows a different explanation, please let us know!

Regards
Klaus H.

The Bowie and Dick test criteria for cycle time @134 is between 3minutes and no greater than 3.5minutes. If the indicator is exposed to longer than 3.5 minutes, the time + heat may cause the indicator to give an incorrect "Pass" result.

I have proves this theory to be correct as I put a Bowie + Dick test pack into a benchtop sterilizer with no air removal set at 135 for 5minutes. The test pack "passed"!

EN285 equilibration time only applies to thermometric testing and cycles with a load. Remember if the chamber is less than 800ltrs the equilibration time is only 15secs.

Hope this helps
Gary