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Autoclave validation | study on temperature Probes

In microbiology, Autoclave validation and Sterilization are important for every Pharmaceutical to ensure good manufacturing quality. The sterility of glassware and media used for analysis is very important for product manufacturing. If any deviation in sterility, it may lead to being a false result.

So data loggers play a very important role in records the temperature at a different stage with the help of Probes.

The number of Probes used depends on the size of the autoclave being validated.

The number of probes is used for autoclave validation.

Autoclave validation temp probes
Temp. Probes image credit http://”Kitmondo LAB”

There are lots of regulatory guidelines on autoclave validation, but Among the different Guidelines, it mostly does not define the number of Probes used in autoclave validation.

During the Slow to Heat study, biological indictors are not mandatory. There is a need to ensure that one should load one load at a time in an autoclave and place more than 12 numbers of temperature probes in the load.

This is because if the load items are more or, the autoclave chamber size is more than 1000L, then we should place > than 12 No probes.

Here while placing the probes, special attention is required to the selection of location, which shall cover all corners, bottom/ upper central part, mid-central part of the autoclave, based on the load items, representative items of a load.

After placing the probes, a programmed cycle should be applied to the load by simultaneously operating the Validator (Datalogger). One should calculate the F0 value (Formula for F0S10^((Measured temperature- 121.1°)/10))x time interval) of dwell time to comply with all requirements.

First, we need to list out the number of loads to be validated in the autoclave and categorize it into porous, non-porous, and mixed loads. It is based on the nature of the load items, which covers rubber bung, silicon tube, cartridge filter, HDPE bottle. It is important to note that heat penetration is very difficult in a porous load. After the categorization of the loads, we should develop the heat penetration cycle, which is known as slow to heat cycle or hardest to heat cycle, or cold spot identification cycle in load.

Here we have to use the same cycle parameters for the slow to heat and final run for all non-liquid loads.

Based on the type of load, items in a load, post pulse rate, number of post pulse can vary because the post parameter will not have any impact on heat penetration or SAL.

All slow to heat run for the different loads should be performed in the cool chamber. After the Slow to Heat study, all loads must be validated for the three consecutive successful runs to prove the consistency, reliability, and SAL in the biological indicators at ten cold spots.

Now for the worst case for the minimum load validation/ Sterile assurance level/ Variable position validation, where one particular load can be considered as a worst-case for the above-mentioned validation out of 4 loads. one will need to perform one half cycle hold time, for instance, the full cycle time is 30 minutes so that 15 minute hold time will be half cycle. There is also a need to adopt the heat penetration study with biological indicators on the worst caseload to prove the 12 log reduction or Sterility Assurance Level (SAL) in full-cycle hold time.

Important things about Thermocouple.

  • Avoid touching of Thermocouple with the wall of the autoclave because on walls have a higher temperature as compared to the chamber.
  • The Thermocouple must keep in the right position, as mentioned in the image.
  • The Thermocouple should follow BS4937 standard part 4 (Nickel-chromium /Nickel-Aluminium) or part 5 (Copper-constantan).
  • The width of the Thermocouple wire should not be more than 0.7 mm.
  • The temperature between the Thermocouple must be controlled. It should not be more than 3⁰C. For example, the should be in between 121⁰C to 124⁰C pressure must be within 15 to 18 lbs for 15min cycle.
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