Tag Archives: steam sterilizers

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Types of Sterilization (Steam, Dry Heat, and Ethylene Oxide)

The need to safely and quickly eliminate all microorganisms from equipment is our driver to choose the best sterilization method available. Although there are numerous physical and chemical processes used for proper sterilization of equipment, there are just a few main ones. With that said, there are three main types of sterilization methods common within the scientific community today. They are steam, dry heat, and ethylene oxide (EtO) sterilization. Understanding how each one of these works as well as their advantages and disadvantages is critical in helping make sound decisions on which method is ultimately best.

Types of Sterilization

Steam Sterilization

types of sterilization: steam

Steam sterilization (aka autoclaving) can be characterized as an effective, fast, safe, and affordable option for sterilization. An autoclave, which is a large steel chamber circulating steam, destroys microorganisms and bacterial spores via high temperatures and pressure. The steam needs to be maintained at approximately 120 degrees Celsius for a minimum of thirty minutes.

While there is a long list of benefits to autoclave sterilization, its non-toxicity and safety for humans are huge ones on the list. Not only can steam sterilization tout the ability to penetrate packaging and sterilize liquids, it also eliminates fire risks unlike dry heat. No doubt that the ability to rapidly sterilize equipment makes steam sterilization attractive to so many. It’s also one of the most economical and environment-friendly sterilization choices available. In addition, it’s known for being easy to control and monitor. Some disadvantages though include that it can’t sterilize heat/moisture sensitive material, has the potential to cause burns, and requires multiple utilities like water and electricity.

Dry Heat Sterilization

A thermal processing option commonly used is dry heat sterilization. This process removes moisture content from coatings and other materials. According to the CDC, this method should only be used “for materials that might be damaged by moist heat or that are impenetrable to moist heat (e.g., powders, petroleum products, sharp instruments).”

Let’s go over some of the benefits of using dry heat for sterilization. First, this non-toxic and environment-friendly option only requires electricity to operate. On top of that, it’s water-conservation friendly and has relatively low operating costs. In contrast, dry heat poses a fire risk and cannot sterilize liquids. Of particular note, dry heat is a very time-consuming sterilization process (4x to 5x longer cycles than steam sterilization). To elaborate on why it takes longer for sterilization with dry heat, it’s largely because of the issues of heating air with very little moisture content. What this means is that in order to accomplish proper dry heat sterilization, increased time and higher temperatures (approx. 180 degrees Celsius) are necessary.

Ethylene Oxide (EtO) Sterilization

Another commonly used way to sterilize equipment with gas is through EtO sterilization. The gas reacts in a way that disrupts cell growth and division, resulting in killing the microorganisms. This process occurs in a dry heat oven.

As for some of the pros to dry heat sterilization, it can be used for heat or moisture sensitive environments; be used on a variety of materials without distortion and functionality disruption; has the ability to penetrate packaging. Moreover, it requires only electricity and there’s cycle flexibility with single-dose cartridges. However, most obvious is the fact that EtO is toxic to humans and doesn’t rate high on the safety factor. Because of its toxicity, items need to be aerated prior to use which is quite time-consuming along with lengthy cycle times. The bottom line is that it’s a carcinogen and is flammable. One must be aware that EtO must be degraded before emission. In general, EtO sterilization is more complex than other methods as it does require multiple steps in the process for effective use.

Conclusion

Choosing a sterilization method is key critical for a variety of reasons. As we know, inappropriate sterilization can cause a lot of problems, with the worst scenarios involving fatalities. As you can see, there are advantages and disadvantages to each and what you are sterilizing becomes an important aspect to consider when making your selection. Based on the literature and research, if one stood apart from the others, it would easily be steam sterilization with its lengthy list of advantages. In conclusion, steam sterilization is a solid, all-around choice and it should be looked at as a first, go-to option for sterilization needs.

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7 of the Most Popular Autoclave Questions

We answer the top questions being asked about autoclaves and the sterilization process.

At Beta Star, our mission is to provide simple and reliable sterilization solutions. Delivering sterilization simply begins with a consistent understanding of steam sterilization solutions through the use of autoclaves, also called steam sterilizers. In preparing for this article, our team dove into Google’s online search results to identify seven of the most frequently asked questions related to autoclaves and the sterilization process they execute. 

1) Why is the standard autoclave temperature set to 121oC?

Sterilization of media, the centric purpose of autoclaves, is designed to reduce the presence of live pathogens that could contaminate the development of pharmaceutical drugs, invalidate the results of research institutions, or allow outside pathogens into vivarium laboratories.

The death of the pathogen, whatever type it may be, is completed by the destruction of the structural and metabolic cell components required for replication. Without the ability to replicate or infect, the pathogen is no longer a threat to the environment around it. While specific pathogens or specific environments may require higher temperatures, 121oC is widely held as the minimum temperature for efficient sterilization. 121oC is necessary, because at 100oC (the boiling point of water under unadulterated atmospheric conditions) endospores are not killed and thus sterilization cannot be fully achieved. In fact, Geobacillus stearothermophilus is used as an indicator to confirm that a successful sterilization cycle was completed. This answer is further vetted in conjunction with question number five.

2) Why are autoclaves being used for media preparation?

Autoclaves are used to prepare many different types of media for their final purpose. They are used to provide sterile media that may be consumed in different applications, such as in vivarium laboratories and food & beverage manufacturing. Media is also studied in microbiology laboratories, tested in innovative research institutions, and distributed for life-saving applications like pharmaceutical medicine or orthopedic facilities. The most important aspect of the autoclaves that deliver sterilization, are their ability to give a biological blank slate to the user. From this blank slate:

  • Media (water, food, etc.) may be consumed safely without contaminants
  • Studies may be completed without the altering presence of an unknown or uncontrolled pathogen
  • Research tests can be completed and replicated, thus ensuring adoption and acceptance of the test results
  • Providing life-saving applications, such as orthopedic devices or COVID-19 testing kits, that are packaged free from pathogens

3) Who invented the autoclave?

The first autoclave-like pressurized vessel, similar to what is now known as a pressure cooker, was built by Denis Papin in 1679! However, it would take another 200 years before the autoclave as we know it would be built. In 1879, Charles Chamberland, working Louis Pasteur (the inventor of the pasteurization process) created the first autoclave for medical and scientific purposes. Want to see a cool photo of a 115-year-old autoclave? Check out the photo of an autoclave built in 1905 by Northwestern Steel and Iron Works.

4) What are autoclave bags used for?

Autoclave bags are used to hold biohazardous items until it is time to be sterilized in an autoclave. The high-density propylene that they are typically made of can withstand temperatures up to 135oC, the high end of nearly all autoclave cycle parameters.  When searching for autoclave bags to use at your facility, it is recommended that the manufacturer of those bags meet the following regulations:

5) How does autoclave sterilization work?

Sterilization in an autoclave (often aptly referred to as a steam sterilizer) works through the manipulation of four aspects vital to effective sterilization: time, temperature, pressure, and steam. They all play an important role in the process of effective sterilization:

  • Time: Proper time ensures that the pathogens have been in the presence of a sterilizing environment (steam at temperature) for a long enough time to facilitate the proper killing of all pathogens.
  • Temperature: Proper temperature of the steam that comes in contact with all pathogens, a minimum of 121°C, ensures the proper destruction of the pathogen’s ability to reproduce.
  • Pressure: Manipulating the pressure in an autoclave’s prevacuum cycle ensures that no air pockets are left remaining in the sterilizing chamber. Air pockets provide insulation to pathogens from the sterilizing environment and are removed during pressure ramping so that the pathogens do not escape proper sterilization.
  • Steam: Transfer of heat is most efficiently done using steam. The steam fills the chamber so that it can come in contact with the entirety of the sterilization load.

6) What are autoclaves used for?

At a foundational level, autoclaves are used to execute the steam sterilization process. They are designed to kill 99.9999% of all pathogens after a successful sterilization cycle is run. This is commonly referred to as a 6-log reduction in living pathogens. For the respective industries that we operate in, autoclaves are commonly used for:

  • Biomedical / Pharmaceutical: In these laboratories, autoclaves are frequently used for the research development of drugs and vaccines.
  • Common Laboratory (Research): in these laboratories, research tools and instruments are the most frequently autoclaved items.
  • Vivarium: to maximize throughput, bulk autoclaves are used in vivarium facilities to sterilize cages and bedding for the protection of research subjects.

7) Can autoclaves kill viruses?

Autoclaves are capable of killing all types of pathogens, including viruses through the effective use of the four tools for sterilization mentioned in the answer to question 5. This has become especially poignant as the world grapples with the COVID-19 pandemic. Killing viruses are important in some applications for sterilizing medical tools and PPE before they are discarded.

Sources

(Question 1) Science Direct
(Question 1) National Center for Biotechnology Information (NIH)
(Question 3) Smithsonian Institute
(Question 4) Tufpak
(Question 5) CDC