Steam Sterilization Cycles

Steam Sterilization Cycles, Part 3: Steam-Air-Mix Cycle

Arthur Trapotsis
Written by: Arthur Trapotsis

MS Biochemical Engineering, MBA, Consultant

When using steam autoclaves, it’s critical to identify, understand, and create the proper sterilization cycle for ALL of your load requirements. So, as part of our series discussing Steam Sterilization Cycles, this third article is designed to explore the Steam-Air-Mix Cycle, a more advanced steam sterilization cycle for unique applications.

Steam-Air-Mix Cycle

Certain types of sterilization loads may require steam sterilization cycles that stray from the standard Gravity, Liquids, or Vacuum types.

Take, for example, sterilizing a liquid-filled syringe using one of the three standard cycles. Immediately a problem is presented here: As the syringe heats up, the liquid inside of the syringe expands, exerting pressure on the stopper that is supposed to hold the liquid inside. This is especially critical when the container is topped-off with liquid (no air inside). If air resides in the container alongside the liquid, that will increase in pressure as well. If the stopper is not able to resist those pressures, the stopper will be forced out of position and may even eject from the syringe body. Now, not only will the syringe be unusable, but whatever was inside of the syringe will have made a mess of the rest of the load and your autoclave chamber.

The obvious solution is to increase the autoclave chamber pressure in order to balance out the internal and external pressure of the syringe (or other sealed container). If the pressure outside of the syringe is equal to the pressure inside, then the stopper should not move. But how is this accomplished?

One way to increase autoclave chamber pressure is to simply inject more steam. Unfortunately, as the steam pressure rises, so does the temperature. When the temperature rises, the contents of the container will heat even more, causing the internal pressure to continue to rise as well.  A Steam-Air Mix Cycle solves this issue by injecting compressed air into the autoclave chamber during the sterilization phase in order to artificially raise the pressure. Steam continues to be injected into the chamber as needed in order to maintain the cycle’s temperature setting.

After the sterilization phase is complete, it is necessary to maintain an elevated chamber pressure during the exhaust phase in order to keep the syringe intact. However, as the temperature falls, the internal pressure of the container will begin to fall as well, potentially causing the reverse-effect where the external pressure from the chamber compromises the container. To solve this, the chamber pressure is slowly reduced as the temperature falls.

To get an overview of steam sterilization, check out our video here:

The Steam-Air Mix Cycle option requires you to have a compressed air supply, and it is recommended for applications where a liquid is being sterilized in a sealed container that may be affected by pressure imbalances.

As always, we at CSS hope this article—and our entire Steam Sterilization Cycles series—helps answer some of your most pressing questions. However, we encourage you contact us at any time with any additional questions or inquiries you may have—our team of experts is always here to help.

17 Questions to Ask Before Buying Your Next Autoclave

17 Questions to Ask Before Buying Your Next Autoclave

With so many models, sizes, options and components to choose from, how can you ever really know exactly what you need to make the most out of your investment?

These questions will help you to make informed decisions by outlining what is most important to consider and know about owning an autoclave.