What Is an Autoclave?

An autoclave is a machine used in industrial and scientific labs to sterilize or decontaminate items.[1] It applies particular heat under pressure to the machine’s chamber to kill harmful pathogens, such as bacteria, fungi, spores, and viruses in and on the items kept in the autoclave vessel.[1]

The items are autoclaved at a specific temperature for a given time. The procedure induces moisture in steam to transfer heat to destroy the protein structure of contaminants or microorganisms and disinfect the items.

Over time, the autoclave technology has improved from being a basic steam sterilizer to enhanced versions with pre-vacuum cycles and steam-flush pressure-pulse features.

The first steam sterilizer

Figure: The first steam sterilizer built by Charles Chamberland in 1880 for medical applications.[2]

The autoclave has a range of applications in areas including dentistry, microbiology, medicine, and veterinary science.[3]

Conduct science Advanced research autoclave

Figure: Advanced research autoclave used today in labs.

This article discusses the working mechanism of autoclaves, materials that can or can’t be autoclaved, and how to use an autoclave safely.

How Does an Autoclave Work?

Autoclave works on the principle of moist heat sterilization. It generates saturated steam under a particular pressure to kill pathogens.

Here’s how it works!

Seal the autoclave after the items, including tools and chemicals, are kept in its chamber. Then, remove the air present in the chamber by:[4]

  • Using gravity displacement units to pump steam into the vessel and replace air with vacuum.
  • Using pre-vacuum that utilizes a vacuum pump to remove the air from the vessel.[4]

As air is removed, steam is pumped into the chamber at higher pressure, which helps achieve the sterilizing temperature in the given duration.[5] The higher the pressure, the higher the temperature inside the chamber.

Higher pressure in the autoclave’s chamber helps heat penetrate deeper parts of the items in it and cause coagulation of microbial proteins, making them inviable.[5]

Steam is continuously supplied in the chamber to maintain the target temperature once it has been reached.

Normally, a temperature of 121°C at the pressure of 15 psi or 775 mmHg is used in labs to sterilize the equipment, tools, and autoclavable chemicals.[5]

Once the sterilization is over, the autoclave’s chamber releases the pressure through a whistle while the machine’s temperature and pressure return to normal.

Illustrative diagram of the working mechanism of the autoclave

Safety Tips to Observe When Using the Autoclave Sterilizer

Though autoclaves are simple to use, there are certain safety measures you need to observe before running the machine:[5]

  • Laboratory personnel should be trained before using the particular model of the autoclave.
  • Do not overcrowd the autoclave and fill the chamber with materials to its brim – proper spacing between the items allows for efficient sterilization.
  • Always place the “to-be-autoclaved” items in the secondary chamber.[5]
  • Only use autoclavable bags to pack and autoclave the packaged materials/waste.[5]
  • Wrap the materials in something to promote better steam penetration. However, do not use aluminum foil.
  • Always ensure that items in the chamber do not touch the chamber’s sides or top.
  • Do not attempt to open the autoclave’s lid while it is running.
  • Autoclave the clean and waste material separately.
  • To prevent liquid spillage, do not fill the liquid-containing vessels with more than ⅔ of their total volume.[5]
  • Never autoclave the liquid components in sealed vessels or containers.
  • Always check for previous items left in the container before pre-heating the autoclave.
  • Always check the water level of the autoclave before autoclaving the items.
  • Close the lids tightly and tighten the screw before switching on the electric heater.[6]
  • Do not open the autoclave before its pressure is fully released, and do not try to touch the materials immediately after sterilization. Let them cool down a bit.
  • Do not seal any autoclavable item as it can cause an explosion hazard.[6]
  • Never stand directly in front of the autoclave door.
  • Perform routine maintenance of the autoclave machine and regularly check its operations.
  • Report to the faculty if any malfunctions are observed, such as:[6]
    • Leaking valves
    • Insufficient temperature
    • Unexpected fluctuations in temperature or pressure during the cycle
    • No steam
    • Gasket deterioration
    • Water leaks from the chamber
    • Insufficient jacket pressure
    • Steam escaping from around the door during the cycle

What Materials Are and Aren't Autoclavable?

An autoclave is an effective way to sterilize equipment, tools, and certain chemicals. However, not all materials can be autoclaved. Therefore, before autoclaving, ensure the material or items can withstand high temperatures and pressure.

Autoclavable materials:

  • Glass: Only autoclave pyrex or pyrex type glass materials. Therefore, before purchasing, ask the vendor about the glass material.[7]
  • Metals: Most metals available in labs can withstand an autoclave environment.
  • Polypropylene-made items: It’s an autoclavable inexpensive resin used to make different bags, trays, and pans.[7]
  • Plastic items: Not all plastics are autoclave safe. Other than products made from polypropylene (PP) and polypropylene copolymer (PPCO), items made from fluoropolymers, such as Teflon PFA, FEP, or ETFE, can be autoclaved.[8]
  • Autoclave polycarbonate items with caution. Do not expose them to steam additives and alkaline detergents. Also, they can only withstand 30-50 autoclaving cycles. However, you should note that sterilizing these materials reduces their mechanical strength.[8]
  • Media solutions, paper and latex gloves placed in biohazardous autoclave waste bags, surgical tools, contaminated solid items, water, hospital linens, and animal food and bedding are autoclavable.[9]

Non-autoclavable materials:

  • Do not autoclave the plastic materials made from HDPE, LDPE, PET, and PETG resins. They can melt and damage your autoclave – instead, sterilize these materials with gas (ethylene oxide formaldehyde).[8]
  • Paper is a combustible substance, so it should not be directly autoclaved. It might catch fire.[5]
  • Do not sterilize water-proof or water-resistant materials like powders and oil with an autoclave.[5]
  • Never autoclave materials that are flammable, toxic, and corrosive (such as phenol, ether, trichloroacetic acid, and chloroform).[10]
  • Do not sterilize household bleach or chlorine-based (or chlorine-containing) products, radioactive materials, acids, low-density (LDPE) and high-density polyethylene (HDPE), materials contaminated with chemotherapeutic agents, or paraffin-embedded tissue using the autoclave.[10]

FAQs on Autoclave Sterilizers

Here are some frequently asked questions by autoclave users:

1. What three things must one do when operating an autoclave to help ensure success?

  • Wear your personal protective equipment (PPE), such as a lab coat and gloves when working with autoclaves.
  • Ensure the items in the autoclave are autoclavable and the containers containing liquid items are not tightly sealed.
  • Do not overcrowd the autoclave, ensure sufficient water is available in the machine and set the proper time and temperature before starting the process.

2. What is the autoclave cycle time frame?

The autoclave sterilization cycle consists of three phases:[3] Purge Phase, Exposure (Sterilization) Phase, and Exhaust Phase – these phases are completed in around 1-1.5 hours.[11]

The autoclave cycle time frame refers to the exposure phase, which varies based on the size, shape, density, weight, and material composition of the items being sterilized.

3. What is the autoclave temperature range?

Autoclave commonly runs at temperatures between 250° F (121° C), 270°F (132°C), to 275°F (135° C).[2] It’s essential to expose the items being sterilized at this temperature for a certain period for complete sterilization.

4. Can an autoclave explode?

Yes, it can. When the seal of the autoclave’s door is malfunctioning, the rapid release of extreme heat and temperature trapped inside the chamber can cause an explosion and severe injury to people around it.

Conclusion

An autoclave is a machine used to sterilize tools and liquid media in labs. It applies high pressure and temperature to disinfect the items in the chamber.

It’s mainly used in scientific, medical, and industrial labs to sterilize a spectrum of items. Currently, scientists are working to create sophisticated autoclaves with advanced technology, toughness, better safety, and upgraded features.

Though an autoclave is easy to use, it can be dangerous to work with if handled carelessly. Therefore, it’s essential to follow the safety guidelines that come with the equipment and ensure that only autoclavable items are autoclaved.

Furthermore, regular maintenance of the machine is required because if the door or other parts of the equipment malfunction, the high pressure and temperature can cause an explosion.

Often in such cases, the quality of the autoclave bought also plays a significant role, hence why you must purchase from trusted vendors only.

At Conduct Science, we provide high-throughput and easy-to-use autoclaves at affordable prices – click to shop for the best autoclave for your research!

References

  1. A Guideline For The Safe Use Of Autoclaves. Retrieved from https://uwaterloo.ca/safety-office/sites/ca.safety-office/files/uploads/files/guideline-for-safe-use-of-autoclaves.pdf
  2. Everything About Autoclaves. Retrieved from https://www.steris.com/healthcare/knowledge-center/sterile-processing/everything-about-autoclaves
  3. What is autoclaving and how is it relevant to liquid handling instruments? Retrieved from https://www.microlit.us/how-autoclaving-is-relevant-to-liquid-handling-instruments/
  4. What Is an Autoclave, and How Does It Work? Retrieved from https://www.generon.com/what-is-an-autoclave-uses-how-does-it-work/
  5. Anupama Sapkota (2022). Autoclave- Definition, Parts, Principle, Procedure, Types, Uses. Retrieved from https://microbenotes.com/autoclave/
  6. Scott Mechler. Your Go-To Guide for Autoclave Safety [w/ Free Checklist!] Retrieved from https://consteril.com/autoclave-safety-checklist/
  7. What Materials Cannot Be Autoclaved? Retrieved from https://www.mesaustralia.com.au/blogs/news/what-materials-cannot-be-autoclaved
  8. What is Autoclaving? Retrieved from https://www.oberk.com/packaging-crash-course/5-questions-about-autoclaving-plastic-bottles-and-glass-bottles
  9. Autoclave compatible materials – What kind of materials can be sterilized in an autoclave? Retrieved from https://celitron.com/en/blog/autoclave-compatible-materials
  10. What Can And Cannot Be Autoclaved. Retrieved from https://www.betastar.com/what-can-cannot-be-autoclaved/
  11. Autoclave Use. Retrieved from https://ehs.princeton.edu/book/export/html/380