Liquids can be problematic in steam sterilization because they can take considerably longer to heat up than most other materials. Additionally, liquids are prone to “boil over” if the proper pressure/temperature relationship is not maintained in the sterilizer during the complete cycle.

Standard Operating Procedure

From PRIMUS’ field experience, the following steps can assist end users in developing a Standard Operating Procedure (SOP) that will help ensure repeatable sterilization results:

Step 1

Establish Standard Liquid Load cycle parameters for every standard configuration of liquid loads to be run in the sterilizer (e.g. 30 one-liter flasks).

If liquid volumes to be processed vary from the standard volume, use the largest volume to determine the appropriate sterilization time. This will represent the worst-case scenario which then may be fine-tuned to smaller liquid volumes.

Step 2

With the Standard Liquid Load in the chamber, insert a thermocouple or other temperature-monitoring device into the center of a liquid container.

PRIMUS offers a Load Probe option which will indicate and print the
temperature of a liquid during sterilization. This can also be used with the
Fo Option (Heat of Lethality) to control the sterilization cycle exposure

Step 3

Configure the initial liquid sterilization cycle for a long sterilization time (well over the estimated time needed). Start the Liquid Cycle and monitor the liquid temperature monitoring device once the sterilizer achieves sterilization temperature.

The sterilization temperature is controlled from the drain RTD as this is the
coolest location within the chamber.

Step 4

Record the elapsed sterilization time at which the liquid temperature monitoring device achieved the desired sterilization temperature.

The amount of time recorded above is added to the desired liquid sterilization time for the Standard Liquid Load. An example is as follows:

  • Time to reach sterilization temperature – 30 minutes
  • Time of sterilization – 15 minutes
  • Total sterilization time configured in the cycle parameters – 45 minutes
  • Once this elapsed time has been noted, continue for the desired sterilization time.

Step 5

Once the Liquid Cycle is complete, run a biological test on the liquid to determine sterilization efficacy.

Step 6

Assuming that the biological testing is acceptable, most facilities repeat the test (with the newly derived sterilization time) three (3) times to validate the Liquid Cycle.

Have a question or having difficulties? Talk to Dave Schall, our PRIMUS sterilizer expert who is here to assist you anytime at 877.679.7800 extension 1212 or email at dschall@spire-is.com.

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