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Number of Temperature Probes for Autoclave Validation

Number of temperature sensors/ thermocouples, their positions and type of thermocouples used during the autoclave validation.
Autoclave validation has a very important role in pharmaceutical sterile manufacturing and also in the microbiology laboratory. Whole sterile manufacturing process depends on proper sterilization of equipments used in manufacturing.

In microbiology laboratory of sterile and non-sterile manufacturing, accuracy of the results depends on the sterility of glassware and media used for analysis of products. Improperly sterilized glassware and media may lead to the false results.

number of temperature sensors in autoclave validation
Data loggers are used to record the temperature at various positions within the sterilizer. Data loggers have multiple channels to record the data captured by the temperature probes or sensors. Number of probes should be used according to the size of the autoclave being validated.

Many pharmaceutical professionals have asked me, how many temperature probes we should use in autoclave validation. Some of them asked it during their regulatory audits when the inspector asked them a reference for the same.

There are various regulatory guidelines that have guidance on autoclave validation. But most of them have not defined the number of probes or thermocouples to be used in validation study.

As per PDA Technical Report 1, minimum 10 thermocouples or 5 thermocouples per 100 cubic feet for large autoclaves are to be used for sterilizer validation but it has not given the volume of large autoclaves. Hence, it is not clear how to implement this guidance.

As per HTM 2010 Part 3 Sterilization: Validation and verification - Paragraph no. 6.9, twelve thermocouples are required in validation of autoclave and one pressure sensor must be there to validate the pressure in the autoclave.

It is little bit confusing that both of above guidelines have different number of probes for autoclave validation. PDA says minimum 10 temperature probes to use but more probes are better. Therefore, it is better to use 12 or more temperature probes.

Before validating an autoclave, you must know the following things about thermocouples.
  • The thermocouple should not be touched to the wall of the autoclave because walls will have higher temperature than the chamber.
  • One thermocouple must be placed near the drain point of the autoclave and one should be placed in each corner.
  • Thermocouples should follow BS4937 standards Part 4 (nickel-chromium/ nickel-aluminium) or Part 5 (copper/constantan).
  • The width of single wire of thermocouple wire should not exceed 0.7 mm.
  • Heat distribution and heat penetration study should be conducted in triplicate.
  • It is essential to achieve 121°C for each thermocouple for defined time period (15 min).
  • The difference between the temperature of thermocouples should not be more than 3 °C i.e. all thermocouple must have temperature between 121 °C and 124 °C during the sterilization cycle.

Autoclave validation must be done carefully and accurately because a lot of deficiencies are found in autoclave validation during regulatory inspections and inspectors always check the validation protocols and reports. It becomes more critical in sterile manufacturing where production equipments are sterilized.

Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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