How does an Autoclave Work and Important Things to Know

What is an Autoclave?

If you're wondering What is an Autoclave? So It is a type of sterilizer machine used primarily to sterilize equipment and supplies by exposing them to high-pressure saturated steam. This process makes them safe for use, especially in medical and laboratory settings. The key to its function is the temp for steam, which is typically around 121°C (250°F). This high temperature, achieved under pressure, is crucial for effective sterilization. In a medical autoclave, this process is used to sterilize surgical instruments, pharmaceutical products, and other items. In a laboratory setting, a lab autoclave performs a similar function for glassware, media, and other equipment. The composite autoclave is a variation used in industrial processes, especially for composite material manufacturing.

The process of how an autoclave works involves increasing the pressure inside the chamber to elevate the boiling point of water, thus allowing the steam to reach higher temperatures. The minimum sterilizing conditions in a steam autoclave typically involve maintaining this high temperature for a specific period, effectively killing all forms of microbes, including spores and viruses. When preparing items for sterilization, it's crucial to understand how to label an autoclave package correctly. This ensures that the contents are correctly identified and that the sterilization process has been completed.

Best Autoclave Machine from AngelUS Medical

Types of Autoclaves

Autoclave machines come in various designs, each tailored to specific sterilization needs in diverse settings. Here's a deeper look into the different types, highlighting the unique features and applications of each.

  • Gravity Displacement Autoclave: The gravity displacement sterilizer is a staple in many settings due to its simplicity and effectiveness. It's particularly favored in autoclave scenarios for routine sterilization of liquids, instruments, and other non-porous items. The natural circulation of steam makes it a reliable choice for everyday sterilization tasks.
  • Vacuum Autoclave: A vacuum autoclave, or steam sterilizer machine, is essential in healthcare settings. It excels in sterilizing porous items, surgical instruments, and wrapped goods. By creating a vacuum, it ensures steam penetration into more complex item assemblies, a key requirement in medical autoclaves.
  • Composite Autoclave: The composite autoclave is engineered for industrial applications. Ideal for manufacturing sectors dealing with high-strength composite materials, these autoclaves apply both high temperature and pressure, ensuring thorough curing and sterilization, critical in producing aerospace components, racing car parts, and other high-performance composites.
  • Pre-vacuum Autoclave: This variant enhances the vacuum process, making it suitable for sterilizing dense loads and items with intricate geometries. It's an advanced version of the vacuum autoclave, often used in settings where the sterility of complex instruments is paramount.
  • Large Industrial Autoclave: Designed for bulk operations, these autoclaves are a cornerstone in industrial sterilization. They are ideal for processing large quantities of products or large items, common in the food processing industry, pharmaceutical manufacturing, and even waste management sectors.
  • Table-Top Autoclave: Smaller in size, table-top autoclaves are a convenient option for small clinics, dental offices, and small laboratories. They offer the functionality of larger units but are designed for limited space and lower volume needs.
  • Dry Heat Autoclave: While not using steam, dry heat autoclaves are crucial in sterilizing items that can't tolerate moisture. They use hot air and are ideal for materials like powders, oils, or certain metal instruments.

How Does an Autoclave Work?

Working Mechanism of AutoClave

An autoclave machine is a marvel of science and engineering, designed to perform the crucial task of sterilization effectively. Understanding how an autoclave works is key to appreciating its significance in maintaining sterility in various industries.

  • Steam Generation: The process begins with the generation of steam, which is a fundamental component in sterilization. Water is heated within the autoclave chamber, raising the temperature above boiling point, typically to temp for steam levels of at least 121°C (250°F). This superheated steam is what makes the autoclave so effective in killing microorganisms.
  • Pressure Build-Up: The autoclave's ability to achieve high-pressure conditions is essential. As steam is generated, the pressure within the chamber increases. The autoclave operates at a pressure of about 15 pounds per square inch (psi), ensuring that the steam can penetrate materials effectively. This high pressure is what sets an autoclave apart from conventional boiling methods.
  • Sterilization Process: Once the desired temperature and pressure levels are reached, the sterilization process begins. Steam, now at the specified temp for steam, permeates every nook and cranny of the items inside the autoclave. This thorough steam penetration is crucial for achieving complete sterilization.
  • Exposure Time: Sterilization isn't instantaneous. Microorganisms require exposure to high temperatures and pressure for a specific duration to ensure their complete destruction. The exposure time varies depending on the load and its contents, but it's a critical factor in achieving sterility.
  • Cooling: After sterilization is complete, the autoclave initiates a cooling process to bring the temperature and pressure back to safe levels. This ensures that items can be safely removed from the autoclave without the risk of burns or exposure to high-pressure steam.
  • Safety Measures: Modern autoclaves are equipped with a range of safety measures to prevent accidents. These include pressure relief valves to control pressure levels and secure locking mechanisms to prevent the autoclave from being opened during operation.

Autoclave Loading and Unloading Procedures

How to load an autoclave

  • Prepare the Load: Ensure items to be sterilized are cleaned and arranged in autoclavable bags or containers as needed.
  • Check the Autoclave: Confirm that the autoclave is clean, in good condition, and equipped with the appropriate cycle settings.
  • Load Placement: Load items evenly, avoiding overcrowding, and leave space for steam circulation. Place heavier items on the bottom and lighter items on top.
  • Position Indicators: Insert biological indicators (BIs) and chemical indicators (CIs) as required for monitoring sterilization. Place them in the most challenging locations within the load.
  • Seal Containers: Ensure containers are properly sealed or capped to prevent contamination during the sterilization process.
  • Documentation: Record load details, including contents, date, and operator's name, for documentation and tracking.
  • Start the Cycle: Close the autoclave door securely, select the appropriate cycle (e.g., gravity, pre-vacuum), and begin the sterilization process.
  • Monitoring: During the cycle, monitor pressure and temperature indicators to ensure they reach the specified levels. Follow the autoclave's operating instructions.
  • Cooling: Allow the autoclave to cool down and depressurize before opening the door. This may take some time.
  • Unload: Carefully remove sterilized items, taking precautions to avoid burns or exposure to hot surfaces.
  • Storage: Store sterilized items in a clean and controlled environment to maintain their sterility until use.
  • Documentation: Document the completion of the sterilization cycle, including cycle parameters and any deviations.

How to unload an autoclave

  • Safety Precautions: Put on appropriate personal protective equipment (PPE), such as heat-resistant gloves and safety goggles, to protect against hot surfaces and potential contaminants.
  • Check for Completion: Ensure that the autoclave has completed the sterilization cycle and has cooled down. Do not attempt to open the autoclave until it is safe to do so.
  • Opening the Door: Carefully open the autoclave door, taking precautions to avoid steam or hot air escaping. Some autoclaves have safety interlocks that prevent the door from opening until safe conditions are reached.
  • Remove Sterilized Items: Gently remove sterilized items one by one from the autoclave chamber. Avoid dropping or damaging the items.
  • Inspect Items: Examine each item for signs of damage or contamination. If any item appears compromised or wet, it should not be used and may need re-sterilization.
  • Cooling Rack: If available, place hot items on a designated cooling rack or surface to cool down before further handling or storage.
  • Dispose of Waste: If there is any waste material, like used autoclave bags or disposable items, dispose of them properly in designated waste containers.
  • Storage: Store sterilized items in a clean and controlled environment, ensuring they remain protected from contamination until they are needed for use.
  • Documentation: Record the unloading process, including any issues or deviations observed during unloading. This documentation is important for traceability and quality control.
  • Cleaning: After unloading, clean the autoclave chamber and racks if necessary, following proper cleaning procedures.
  • Shutdown: If the autoclave is no longer in use, shut it down following manufacturer guidelines, and secure the area.
  • Maintenance: Report any issues or irregularities observed during unloading to the maintenance or quality control team for further investigation and action.

Autoclave safety precautions

Safety Precaution while using an Autoclave

  • Training and Familiarity: Only trained personnel should operate an autoclave. Familiarize yourself with the specific autoclave's operating manual and safety features.
  • Check Autoclavable Material: Verify that all items are autoclavable. Certain materials can melt, explode, or release toxic fumes when subjected to high pressure and temperature.
  • Proper Loading: Load the autoclave correctly. Overloading or improper loading can lead to ineffective sterilization and accidents. Ensure steam can circulate freely around the items.
  • Wear Protective Gear: Always wear appropriate personal protective equipment (PPE) like heat-resistant gloves, lab coat, and eye protection.
  • Check Seals and Locks: Regularly inspect the autoclave for any wear and tear, especially the door seals and locking mechanisms. A faulty seal can lead to steam leaks.
  • Monitor Pressure and Temperature: Be mindful of the temperature and pressure inside the autoclave. Do not attempt to open the door if the autoclave is pressurized.
  • Allow Cooling Time: After the cycle is complete, allow time for the items and the autoclave to cool before opening. Opening too soon can lead to burns or a burst of steam.
  • Handle Contents Carefully: When unloading, handle contents with care as they will be hot and may contain hot liquids. Use tongs or a suitable tool to remove items.
  • Routine Maintenance: Ensure regular maintenance of the autoclave. This includes checking valves, gaskets, and pressure and temperature gauges.
  • Emergency Procedures: Know the emergency procedures in case of an autoclave malfunction or accident. This includes knowing how to safely depressurize the autoclave and whom to contact for assistance.
  • Inspection Before Use: Inspect the autoclave for any signs of wear or damage, especially the door seal and locking mechanism, before each use. Report and address any issues immediately.
  • Proper Documentation: Maintain logs for autoclave use, including dates, cycle parameters, and maintenance activities, to ensure traceability and accountability.

Autoclave maintenance and troubleshooting

  1. Regular Maintenance: Regular maintenance of your autoclave is essential to ensure its longevity and reliability. This includes checking and cleaning filters, seals, and valves, and ensuring that all components are in good working condition.
  2. Daily Checks: Perform daily checks for any visible signs of wear or damage, especially on door seals, gaskets, and locking mechanisms. Ensure that the chamber and trays are clean and free of debris.
  3. Scheduled Servicing: Adhere to the manufacturer’s recommended schedule for professional servicing. This usually involves more detailed checks and replacement of worn parts.
  4. Record Keeping: Keep a log of maintenance and servicing activities. This helps in tracking the autoclave’s performance over time and can be useful for identifying recurring issues.
  5. Troubleshooting Common Issues:
  • No Heat: If the autoclave isn’t heating, check the power source and fuses. Ensure that the door is properly sealed and locked.
  • Incomplete Sterilization: This could be due to improper loading, low temperature, or insufficient steam. Ensure that the autoclave is not overloaded and that the temperature and pressure settings are correct.
  • Water Problems: Issues like no water in the chamber or poor-quality steam can often be traced back to water supply problems. Check the water level sensors and filters.
  • Pressure Problems: If the autoclave is not reaching the correct pressure, inspect the door seal and steam generator. Blocked vents or a faulty pressure valve could be the cause.
  • Error Messages: Refer to the autoclave’s manual for specific error codes and their meanings. Some issues might require resetting the system, while others might need professional attention.
  • Unusual Noises: Strange noises can indicate a mechanical issue. Listen for hissing (steam leaks), clunking (mechanical problems), or grinding (pump or motor issues). Turn off the autoclave and consult a technician if you notice unusual sounds.
  • Poor Sterilization Results: Check if the load is properly organized and not overloaded. Ensure that the correct cycle type and parameters are being used for the materials being sterilized. Test the autoclave with biological indicators to ensure it is sterilizing effectively.

Repairs and Maintenance 

How to maintain an autoclave

Maintenance Task



Wipe down exterior


Use a damp cloth to clean the outside of the chamber and control panel.

Inspect door gasket


Check for tears or damage in the door gasket.

Check water level


Verify the water level in the reservoir and add distilled water if needed.

Drain condensate collector (if present)


Empty the condensate collector if your autoclave has one.

Run blank cycle


Run a cycle with only water to remove accumulated contaminants.

Clean chamber interior


Use a mild detergent solution to clean the chamber interior; follow the manufacturer's instructions.

Clean door gasket


Clean the door gasket with soapy water and a soft brush.

Inspect drain lines


Check the drain lines for any blockages.

Check steam trap


Ensure the steam trap is functioning correctly.

Lubricate hinges and door mechanisms (if applicable)


Apply lubrication to hinges and door mechanisms if necessary.

Perform biological indicator test


Conduct a biological indicator test to verify sterilization efficacy.

Qualified technician inspection and service


Schedule a qualified technician to inspect and service the autoclave, including safety valves, pressure gauges, and electrical components.

Full preventative maintenance service


Arrange a comprehensive preventative maintenance service by a qualified technician, including a thorough inspection, cleaning, and replacement of worn-out parts.

Autoclave validation and testing

  • Installation Qualification (IQ): This is the initial validation process performed after the installation of the autoclave. It ensures that the autoclave is installed correctly and includes checking that all components are properly installed, the autoclave is connected to the correct utilities, and all safety systems are functional.
  • Operational Qualification (OQ): This step tests the autoclave under normal operating conditions to ensure it functions according to its specifications. This involves running the autoclave through its various cycles (such as vacuum, steam sterilization, drying phases) and verifying that it meets the predefined criteria for each cycle, like reaching the correct temperature and pressure for the appropriate duration.
  • Performance Qualification (PQ): This phase involves testing the autoclave's performance with actual loads. The objective is to ensure that the autoclave consistently delivers the required sterilization conditions across all parts of the load. This is typically the most extensive testing phase and may include multiple runs to validate consistency.
  • Biological Indicators (BI) Testing: Biological indicators, which contain highly resistant spores, are used to challenge the autoclave's ability to achieve sterilization. BIs are placed in various locations within the autoclave and in the most challenging locations within the load. After the cycle, the BIs are incubated to see if any spores survive. Successful sterilization is indicated by no growth of spores.
  • Chemical Indicators: These indicators change color or form when exposed to certain conditions (like temperature and steam) and are used in every cycle to provide immediate visual confirmation that some sterilization conditions have been met.
  • Physical Monitors: These include the autoclave's built-in pressure and temperature sensors and gauges. The data from these monitors should be recorded for each cycle to ensure that the physical parameters required for sterilization are being consistently achieved.
  • Documentation and Record Keeping: Maintaining comprehensive records of all validation and testing processes is essential for regulatory compliance and for maintaining a historical record of autoclave performance.
  • Regular Revalidation: Autoclave validation is not a one-time process. Regular revalidation is necessary to ensure ongoing compliance and performance, especially after any significant repairs, modifications, or relocation of the equipment.

Why is it important to validate and test autoclaves?

  • Ensuring Sterilization Efficacy: The primary purpose of an autoclave is to sterilize equipment and materials effectively. Validation and testing confirm that the autoclave can achieve and maintain the conditions necessary to kill all microorganisms, including bacteria, viruses, and spores, thus ensuring the sterility of the items processed.
  • Safety: Properly functioning autoclaves are vital for maintaining a safe environment. In healthcare, for instance, sterilization prevents the transmission of infections and diseases. Faulty sterilization can lead to contamination, posing serious health risks to patients and staff.
  • Compliance with Regulations and Standards: Many industries are governed by strict regulatory standards (such as those set by the FDA, WHO, or ISO) regarding sterilization. Regular validation and testing of autoclaves ensure compliance with these regulations, helping to avoid legal and financial penalties and, in some cases, closure of facilities.
  • Quality Assurance: Regular testing and validation are part of quality control procedures. They ensure that the autoclave performs consistently and reliably, which is essential for maintaining high-quality standards in the production and preparation of medical and pharmaceutical products.
  • Preventing Downtime and Costly Repairs: Regular testing can identify potential issues before they become serious problems. This proactive approach can prevent downtime due to equipment failure and avoid costly emergency repairs or replacement of the autoclave.
  • Documentation and Record Keeping: Validation and testing provide a documented record of the autoclave's performance. This documentation can be crucial for audit purposes, troubleshooting, and maintaining a historical record for analysis and improvement.
  • Optimizing Operational Efficiency: Regular testing helps in fine-tuning the autoclave's operations, ensuring that cycles are running as efficiently as possible. This can lead to energy savings, reduced wear and tear on the equipment, and optimized cycle times.

Autoclave applications in different industries

Medical and Healthcare:

  • Sterilization of Medical Equipment: Autoclaves are extensively used to sterilize surgical instruments, medical devices, and laboratory equipment to prevent infections and ensure patient safety.
  • Sterilization of Personal Protective Equipment (PPE): During the COVID-19 pandemic, autoclaves played a crucial role in sterilizing PPE like masks and gowns for reuse when shortages occurred.
  • Pharmaceutical Production: Autoclaves sterilize equipment, containers, and media used in pharmaceutical manufacturing to maintain product quality and safety.

Laboratories and Research:

  • Sterilization of Lab Equipment: Autoclaves are essential in research laboratories for sterilizing glassware, culture media, and instruments to avoid cross-contamination and ensure reliable results.
  • Preparation of Culture Media: Autoclaves are used to prepare sterile culture media for microbiological studies.
  • Sterilization of Waste: Autoclaves can sterilize laboratory waste, such as biohazardous materials, before disposal.

Food and Beverage:

  • Canning and Food Preservation: Autoclaves are used in the canning industry to sterilize food products, increasing their shelf life and safety.
  • Brewing and Winemaking: Autoclaves are used for sterilizing containers, equipment, and yeast cultures in the production of alcoholic beverages.
  • Baking Industry: In commercial baking, autoclaves are used for sterilizing equipment and utensils.

Aerospace and Manufacturing:

  • Composite Curing: Autoclaves are employed in the aerospace industry for curing composite materials, ensuring their structural integrity.
  • Manufacturing of Rubber and Tires: Autoclaves are used for curing rubber and vulcanizing tires.

Research and Development:

  • Material Testing: Autoclaves are used to subject materials to extreme conditions of temperature and pressure for research and testing purposes.
  • Chemical Synthesis: In chemistry labs, autoclaves are used for various chemical reactions that require high temperatures and pressures.

Dental and Veterinary:

  • Dental Instrument Sterilization: Autoclaves are used in dental clinics to sterilize instruments and equipment.
  • Veterinary Clinics: Veterinary practices use autoclaves for sterilizing surgical instruments and equipment.

Frequently Asked Questions

Q. What are the typical sterilization cycles for an autoclave?

  • Gravity Cycle: Uses gravity to remove air from the chamber before sterilization.
  • Pre-vacuum Cycle: Removes air from the chamber using a vacuum pump.
  • Steam Flush Pressure Pulse (SFPP): Uses alternating cycles of steam and pressure for effective sterilization.
  • Liquid Cycle: Designed for sterilizing liquids in containers to prevent boil-over. These cycles vary in their application, with selection depending on the type of load and sterilization requirements.

Q. How long does it take to sterilize an item in an autoclave?

A. The duration of sterilization in an autoclave can vary depending on factors such as the type of item, its size, and the chosen sterilization cycle. In general, sterilization cycles typically range from 15 to 45 minutes, with some cycles lasting longer for complex loads or specialized materials. Pre-vacuum cycles tend to be shorter due to their efficiency, while gravity cycles may require more time. It's essential to follow manufacturer recommendations and cycle parameters to ensure effective sterilization while minimizing cycle duration.

Q. What is the maximum temperature and pressure of an autoclave?

A. The maximum temperature of an autoclave typically ranges from 121°C (250°F) to 134°C (273°F) for standard sterilization cycles. The maximum pressure typically reaches around 15 psi (pounds per square inch) or 1.05 kg/cm² during sterilization cycles. However, specialized autoclaves used in certain industries may achieve higher temperatures and pressures for specific applications.

Q. What are the safety precautions for using an autoclave?

  1. Always wear appropriate personal protective equipment (PPE), including heat-resistant gloves and safety goggles.
  2. Ensure proper loading, as overloading can impact sterilization effectiveness.
  3. Never open the autoclave door until it has depressurized and cooled to a safe temperature.
  4. Follow manufacturer instructions for loading, cycle selection, and maintenance to prevent accidents and ensure sterilization efficacy.

Q. How do I maintain my autoclave?

A. To maintain your autoclave, perform daily checks for water levels and clean the interior. Conduct weekly cleaning of trays and racks, inspect the door gasket, and clean the drain strainer. Additionally, schedule professional servicing every six months for calibration and thorough inspections.

Q. How often should I have my autoclave serviced?

A. It's recommended to have your autoclave professionally serviced every six months to ensure its optimal performance, calibration, and safety. Regular servicing helps prevent issues and extends the autoclave's lifespan.

Q. Do autoclaves disinfect and sterilize?

A. Autoclaves are primarily designed for sterilization, which is the complete elimination of all forms of microorganisms, including bacteria, viruses, and spores. While sterilization processes are highly effective at disinfection, they go beyond standard disinfection methods by achieving a higher level of microbial destruction.

Q. What substance Cannot be sterilized in an autoclave?

A. Substances that cannot be effectively sterilized in an autoclave include heat-sensitive materials like plastics that may deform or melt at the high temperatures used in autoclaving. Additionally, substances that are sensitive to moisture or pressure changes may be damaged during the sterilization process.

Q. Can you leave stuff in an autoclave overnight?

A. Leaving items in an autoclave overnight is not recommended. Autoclaves should be operated under supervision to ensure proper sterilization and prevent potential issues like overexposure to heat and moisture, which can damage both the items being sterilized and the autoclave itself.