Autoclave – Definition, Principle, Parts, Operating Procedure, Uses

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What is an autoclave?

  • An autoclave is a machine that utilizes moist heat in the form of saturated steam under pressure to achieve sterilization. It is widely used in various industries, including healthcare facilities and laboratories, for its ability to destroy microorganisms such as bacteria, viruses, fungi, and spores.
  • The primary principle behind autoclave sterilization is the application of high temperature and pressure to effectively kill the harmful organisms present in the material being sterilized. By subjecting the material to steam at a temperature above the boiling point, typically around 135-137°C, for a specific duration, the autoclave ensures the elimination of pathogens.
  • One of the key advantages of autoclave sterilization is its non-toxic nature, making it safe for use on different types of materials. It is also a cost-effective method that rapidly eliminates microorganisms, including spores, and can efficiently penetrate tissues.
  • Autoclaves come in various sizes, shapes, and functionalities to accommodate different applications. They are capable of sterilizing liquids, solids, cavities, surgical materials, and laboratory instruments of different sizes and shapes. This versatility makes autoclaves suitable for a wide range of scientific and industrial purposes.
  • The importance of autoclaves extends beyond sterilization in healthcare settings. They are also used in industrial and scientific processes that require elevated temperatures and pressures. For instance, autoclaves play a crucial role in the chemical industry for curing coatings and vulcanizing rubber. In addition, they are utilized in hydrothermal synthesis and the manufacturing of composites.
  • The history of autoclaves dates back to the late 17th century when Denis Papin invented a precursor known as the steam digester. However, the autoclave as we know it today was invented by Charles Chamberland in 1879. The term “autoclave” originates from the Greek word “auto,” meaning self, and the Latin word “clavis,” meaning key, symbolizing a self-locking device.
  • In conclusion, an autoclave is a powerful machine that employs steam under pressure to achieve effective sterilization. It is widely used across various industries due to its ability to rapidly and efficiently eliminate bacteria, viruses, fungi, and spores. The versatility and reliability of autoclaves make them essential tools for maintaining cleanliness, safety, and sterility in healthcare facilities, laboratories, and industrial settings.
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Definition of Autoclave

An autoclave is a machine that uses steam under pressure to sterilize materials by killing bacteria, viruses, and spores.

Who Invented The Autoclave Machine?

  • The autoclave machine, as we know it today, has its origins in the steam digester, a prototype that was invented by French physicist Denis Papin in 1679. This early version of the autoclave was essentially a pressure cooker. However, it wasn’t until 1879 that the French microbiologist Charles Chamberland refined and developed a new version of the autoclave specifically for medical applications.
  • The field of disinfection and sterilization took a significant step forward in 1881 with the research conducted by Robert Koch. Koch’s studies focused on the disinfecting properties of steam and hot air, and he demonstrated that moist heat, in the form of steam, had superior penetration capabilities compared to dry heat. This finding paved the way for the advancement of autoclave technology.
  • In 1933, modern autoclave technology was introduced with the development of the first pressure steam sterilizer that incorporated temperature measurement in the chamber drain line through a thermostatic trap. This innovation provided a means to control and verify the performance of the autoclave by monitoring temperature and eliminating air. Prior to this development, pressure was the sole indicator of control, and there was no method to accurately measure temperature or ensure proper air elimination.
  • Since then, autoclave technology has continued to evolve. In 1958, pre-vacuum cycles were introduced, followed by the introduction of steam-flush pressure-pulse cycles in 1987. These advancements have contributed to the refinement and improvement of autoclaves, or steam sterilizers, that are widely used in hospitals and other medical settings today.
  • Overall, the autoclave machine has a rich history of innovation and development, with contributions from notable inventors and scientists, leading to the highly efficient and effective sterilization equipment we have today.

Temperature of Autoclave

  • Autoclave temperature refers to the specific range of temperatures used in steam sterilization to effectively kill microorganisms. There are various temperature ranges utilized for this purpose, with the most common ones being 121°C (250°F) and 132°C (270°F).
  • These temperatures have proven to be highly effective in destroying bacteria, viruses, fungi, and spores, ensuring a thorough sterilization process. The choice of temperature depends on the specific requirements of the materials being sterilized and the type of microorganisms targeted.
  • A temperature of 121°C (250°F) is widely used in autoclaves for sterilization purposes. This temperature, along with the application of pressure, achieves rapid microbicidal and sporicidal effects. It is commonly employed in healthcare facilities and laboratories for the sterilization of medical instruments, laboratory equipment, and other heat-resistant materials.
  • Another frequently used temperature is 132°C (270°F). This higher temperature offers increased efficiency in killing microorganisms and is often utilized in situations where a higher level of sterilization is required. Certain sensitive materials or specific applications may necessitate this elevated temperature to ensure complete eradication of pathogens.
  • It is important to note that autoclaves may also employ other temperature ranges, such as 135°C (275°F), depending on the specific needs and protocols of the sterilization process. The chosen temperature range should align with industry guidelines, standards, and the specific requirements of the materials being sterilized.
  • In summary, autoclave temperature plays a crucial role in achieving effective sterilization. The commonly used temperatures of 121°C (250°F) and 132°C (270°F) have proven to be highly effective in killing microorganisms, ensuring the safety and sterility of materials. The selection of the appropriate temperature range depends on the specific application, material type, and desired level of sterilization.

Autoclave Working Principle

The working principle of an autoclave is based on moist heat sterilization using steam under pressure. It operates by subjecting the material inside the chamber to steam at a higher temperature achieved through increased pressure.

Under normal atmospheric pressure, water boils at 100°C. However, when pressure is increased, the boiling point of water also increases. In an autoclave, the pressure is elevated, allowing the water to reach a boiling point of 121°C (250°F) at a pressure of 15 psi (775 mm Hg). This higher temperature aids in achieving effective sterilization.

The increased pressure in the autoclave chamber enables rapid heat penetration into the material being sterilized. The moisture present in the steam leads to the coagulation of proteins, causing irreversible damage to the function and activity of microorganisms. As a result, the microbes are killed.

During the sterilization process, the steam comes into contact with the material’s surface, releasing latent heat and effectively eliminating the microbes. The condensed liquid ensures the moist killing of the microorganisms, enhancing the sterilization efficacy.

Once the sterilization phase is completed, the pressure inside the chamber is released through a whistle or pressure valve. The pressure is gradually restored back to the ambient pressure, while the sterilized components inside the autoclave remain hot for a certain period.

The working principle of an autoclave emphasizes the importance of four key parameters: steam, pressure, temperature, and time. Dry saturated steam is the ideal form of steam for sterilization. Pressure is employed to achieve the high temperatures necessary for rapid microbial eradication. Specific temperatures, such as 121°C (250°F) or 132°C (270°F), must be reached and maintained for the required duration to ensure effective sterilization. The sterilization time varies depending on factors such as the type of item, whether it is wrapped or unwrapped, and the type of sterilizer being used.

Autoclave Principle or Working.
Autoclave Principle or Working.

How Does an Autoclave Work?

An autoclave operates based on principles similar to those of a pressure cooker. The process involves locking the door to form a sealed chamber and replacing all the air within that chamber with steam. The steam is then pressurized to reach the desired sterilization temperature for a specific duration. Once the sterilization cycle is complete, the steam is exhausted, and the sterilized items can be safely removed.

The sterilization cycle consists of several phases:

  1. Purge Phase: Steam flows through the autoclave, displacing the air and gradually increasing the temperature and pressure.
  2. Exposure (Sterilization) Phase: The autoclave’s control system closes the exhaust valve, causing the interior temperature and pressure to rise to the desired setpoint. The temperature is then maintained at the desired level for the required sterilization time.
  3. Exhaust Phase: Pressure is released from the chamber through the exhaust valve, returning the interior to ambient pressure while the contents remain hot.

To ensure successful steam sterilization, three factors are critical: time, temperature, and steam quality. Autoclaves remove air from the chamber during the conditioning phase, as air inhibits sterilization. This can be achieved through a vacuum system or a series of steam flushes and pressure pulses. Gravity-type sterilizers use steam to displace the air and force it down the sterilizer drain.

After the air removal phase, the exposure phase begins. Steam is continuously admitted into the chamber, rapidly increasing the pressure and temperature to the desired level. The items in the autoclave are held at the sterilization temperature for a specified duration to ensure proper sterilization.

In the final phase, the exhaust phase, the sterilizer drain is opened, and steam is removed, depressurizing the chamber and allowing the sterilized items to dry.

The quality of steam is crucial for effective autoclave sterilization. Ideally, the steam used should be composed of 97% steam (vapor) and 3% moisture (liquid water). This composition ensures efficient heat transfer. Superheated steam, which has a moisture content of less than 3%, is too dry for effective heat transfer and is not suitable for steam sterilization.

By following these processes and ensuring the right conditions of time, temperature, and steam quality, autoclaves can effectively sterilize medical devices and other items in healthcare settings.

How Does an Autoclave Work?
How Does an Autoclave Work? | Image Source:

What Is The Autoclave Cycle Time Frame?

  • The autoclave cycle time frame consists of different phases, including the exposure time, which is the duration required to sterilize the device. However, it’s important to note that the exposure time is only a part of the entire cycle time.
  • The exposure time in steam sterilization is determined based on scientific testing and takes into account various factors such as the size, shape, weight, density, and material composition of the device being sterilized. These factors influence the time needed to ensure effective sterilization.
  • It’s important to adhere to the recommended exposure periods for steam sterilization to achieve the desired level of sterilization. The specific cycle time frame can vary depending on the sterilization method used and the characteristics of the items being sterilized.
  • Overall, the autoclave cycle time frame is determined by considering the exposure time required for proper sterilization, along with other factors such as pre-cycle conditioning, air removal, pressurization, and the subsequent drying phase. These factors collectively contribute to the total cycle time required for a successful autoclave sterilization process.

Factors Affecting Sterilization Effectiveness

Several factors can affect the effectiveness of sterilization in an autoclave. It is important to consider these factors to ensure optimal sterilization results. Here are some key factors to be aware of:

  1. Cleaning: Failure to properly clean instruments before sterilization can lead to increased bioburden, protein burden, and salt concentration. These contaminants can reduce the effectiveness of sterilization. Thorough cleaning of instruments is essential to remove organic and inorganic residues.
  2. Salt: Residual salt on instruments or materials can interfere with the sterilization process and decrease its effectiveness. It is important to ensure that items are properly cleaned and free from salt deposits.
  3. Restricted Flow: The sterilant, typically steam, must come into contact with microorganisms to achieve effective sterilization. Objects with complex designs or sharp bends that inhibit proper steam circulation may prevent the sterilant from reaching all areas, reducing the sterilization effectiveness.
  4. Protein: Residual proteins on instruments or materials can interfere with the sterilization process. Proper cleaning procedures should be followed to remove protein residues effectively.
  5. Microbial Load: The initial microbial load on instruments or materials can impact the effectiveness of sterilization. Higher microbial loads may require longer sterilization cycles or additional measures to ensure thorough sterilization.
  6. Cluttered Autoclave: It is important to avoid overcrowding the autoclave chamber. Sufficient space should be left for steam circulation around the items being sterilized. Cluttered autoclaves may result in inadequate steam penetration and uneven sterilization.
  7. Difference in Cleanliness: It is recommended to autoclave clean and waste items separately to prevent cross-contamination and ensure proper sterilization of both types of items.
  8. Positioning: Items placed inside the autoclave chamber should not touch the sides or top of the chamber. Sufficient spacing should be maintained to allow steam to circulate around the items uniformly.
  9. Appropriate Cycle Selection: Choosing the correct sterilization cycle is crucial for effective sterilization. Using the wrong cycle may lead to inadequate sterilization, damage to the autoclave, liquid overflow, or breakage of bottles or containers.

By considering and addressing these factors, the effectiveness of sterilization in an autoclave can be optimized. Following proper cleaning procedures, ensuring proper positioning and spacing of items, and selecting the appropriate cycle can contribute to reliable and effective sterilization results.

Mode of Action of Autoclave – How does the autoclave destroy bacteria?

  • The autoclave, as a device that utilizes heat for sterilization, works by subjecting the materials or objects to moist heat at high temperatures. The mode of action of an autoclave involves the destruction of bacteria and other microorganisms through the application of heat.
  • Moist heat is highly effective in killing microorganisms due to its ability to denature and coagulate the proteins and enzymes present in the bacterial cells. When the materials are exposed to high temperatures in the autoclave, the heat penetrates the cells, causing the proteins and enzymes to undergo irreversible changes in their structure.
  • This denaturation and coagulation of proteins disrupt the essential functions of the bacterial cells, rendering them non-viable and unable to replicate or cause infections. The high temperatures achieved in the autoclave, typically around 121°C (250°F) or higher, ensure that the microorganisms are effectively destroyed.
  • Additionally, the presence of moisture in the autoclave further enhances the sterilization process. Moist heat is more effective than dry heat in penetrating the microorganisms and facilitating the denaturation of proteins. The combination of heat and moisture in the autoclave creates an environment that is lethal to bacteria, viruses, fungi, and other types of microorganisms.
  • By subjecting the materials to the appropriate temperature and pressure for a sufficient duration, the autoclave ensures that the microorganisms present on the surfaces or within the objects are thoroughly destroyed. This makes the autoclave a reliable method for achieving sterilization and preventing the transmission of infections.
  • It is important to note that the mode of action of the autoclave is primarily based on heat, and it is not suitable for all types of materials. Certain heat-sensitive items or substances may require alternative sterilization methods to ensure their safety and efficacy.
  • Overall, the autoclave’s mode of action relies on the destructive effects of moist heat, leading to the coagulation and denaturation of proteins and enzymes in microorganisms, effectively eliminating their ability to survive and propagate.

Autoclave Parts/ Components

A simple autoclave contain these following components such as;

1. Pressure Chamber/Vessel

  • The pressure chamber is a crucial component of a steam autoclave, serving as the main vessel where the sterilization process takes place. It typically consists of two main parts: the inner chamber and the outer jacket.
  • The inner chamber is constructed using materials such as stainless steel or gunmetal. These materials are chosen for their durability, resistance to corrosion, and ability to withstand high pressure and temperature conditions. The inner chamber is designed to safely accommodate the materials or items that need to be sterilized.
  • Surrounding the inner chamber is the outer jacket, which is typically made of iron. The outer jacket acts as a protective casing for the inner chamber, providing structural support and insulation. In autoclaves used in healthcare laboratories, the outer jacket may be filled with steam to reduce the time required to reach the desired sterilization temperature. This steam-filled jacket helps in maintaining a consistent temperature within the autoclave and aids in achieving efficient and rapid sterilization.
  • The size of the pressure chamber can vary depending on the specific autoclave model and application requirements. Autoclaves come in a range of sizes, with the capacity of the pressure chamber typically ranging from 100 liters to 3000 liters. The size of the pressure chamber determines the volume of materials that can be sterilized in a single cycle.
  • Overall, the pressure chamber is a vital component of an autoclave, providing a controlled environment for the sterilization process. It is designed to withstand high pressure and temperature conditions while securely holding the items or materials to be sterilized. The size of the pressure chamber determines the capacity of the autoclave, allowing for the sterilization of various volumes of materials in a single operation.

2. Lid/ Door

The lid or door of an autoclave is a critical component that serves multiple functions to ensure the sterilization process is carried out effectively and safely.

The primary purpose of the lid is to create a sealed environment inside the autoclave, isolating it from the outside atmosphere. This seal is achieved through the use of screw clamps and an asbestos washer, which make the lid airtight.

The lid of an autoclave incorporates several important components:

  1. Pressure Gauge: A pressure gauge is typically located on the lid of the autoclave. It provides a visual indication of the pressure generated inside the autoclave during the sterilization process. The pressure gauge is essential for monitoring the working condition and safety of the autoclave operation.
  2. Pressure Releasing Unit/Whistle: Similar to a pressure cooker, the autoclave lid is equipped with a whistle. This pressure releasing unit helps control the pressure inside the chamber. When the pressure reaches a certain level, the whistle lifts itself, releasing a specific amount of vapor to maintain the desired pressure. This mechanism ensures that the pressure inside the autoclave remains within safe and controlled limits.
  3. Safety Valve: The presence of a safety valve on the autoclave lid is crucial in situations where the autoclave malfunctions or the pressure inside increases uncontrollably. The safety valve acts as a safeguard by releasing excess pressure. It is designed with a thin layer of rubber that will burst when the pressure exceeds a predetermined threshold. This bursting of the rubber layer allows the pressure to escape, preventing the risk of explosion and ensuring the safety of the autoclave and its surroundings.

These components on the lid of the autoclave contribute to maintaining a controlled and safe environment during the sterilization process. The pressure gauge allows for pressure monitoring, while the pressure releasing unit and safety valve offer mechanisms to prevent excessive pressure buildup and potential hazards. Together, these features ensure the effective and secure operation of the autoclave.

3. Steam generator/ Electrical heater

  • The steam generator or electrical heater is an essential component of an autoclave, located underneath the chamber. Its main function is to heat the water and generate steam within both the inner and outer chambers of the autoclave.
  • Using an electric heating system, the steam generator or electrical heater applies heat to the water, converting it into steam. This steam is then utilized for the sterilization process inside the autoclave chamber.
  • The water level within the inner chamber is crucial for the proper functioning of the steam generator or electrical heater. Insufficient water can lead to the heating system burning out, causing damage and potentially rendering the autoclave inoperable. Therefore, it is essential to ensure that the water level is maintained at an appropriate level to facilitate efficient steam generation.
  • Conversely, an excess amount of water in the inner chamber can pose a problem as well. If the water level is too high, it may interfere with the trays and other components placed inside the chamber for sterilization. Proper water management and control are necessary to avoid any interference or damage to the materials being sterilized.
  • The steam generator or electrical heater plays a vital role in the autoclave by providing the necessary heat to generate steam. It is essential to maintain the proper water level to ensure the effective and safe operation of the autoclave, without compromising the sterilization process or the integrity of the items being sterilized.

4. Vacuum generator (if applicable)

  • In certain types of autoclaves, a separate vacuum generator is incorporated as a component of the sterilization system. This vacuum generator serves the purpose of removing air from the chamber, creating a vacuum environment inside.
  • The presence of air pockets within the autoclave chamber can pose a risk as they may provide a conducive environment for the growth and survival of various microorganisms. These air pockets can act as potential reservoirs for bacteria, viruses, or fungi, compromising the efficacy of the sterilization process. By creating a vacuum inside the chamber, the vacuum generator helps eliminate these air pockets, reducing the likelihood of microbial contamination.
  • The vacuum chamber in an autoclave is an important addition that enhances the sterilization process. By removing air and creating a vacuum, it ensures that the sterilization conditions are optimized for efficient microorganism eradication. This is particularly crucial in applications where absolute sterility is required, such as in medical and laboratory settings.
  • By incorporating a vacuum generator, autoclaves can achieve a more thorough sterilization process by eliminating air and creating an environment less conducive to microbial growth. This additional feature enhances the overall effectiveness of the autoclave, providing a higher level of sterilization assurance.

5. Wastewater cooler

  • In order to prevent any potential damage to the drainage pipes, many autoclaves are equipped with a wastewater cooler system. This system is designed to cool down the effluent or wastewater generated during the autoclave sterilization process before it is discharged into the drainage system.
  • During the sterilization process, the autoclave generates hot water or steam as a byproduct. If this hot water is directly discharged into the drainage pipes, it can cause damage to the pipes due to the high temperatures. The hot water may lead to pipe degradation, corrosion, or even potential leaks.
  • To mitigate these risks, autoclaves are equipped with a wastewater cooler. The cooler system is specifically designed to lower the temperature of the effluent before it enters the drainage pipes. By reducing the temperature, the wastewater cooler ensures that the effluent is at a safe temperature for discharge, minimizing the potential for pipe damage.
  • The wastewater cooler typically employs various cooling mechanisms, such as heat exchange systems or cooling coils, to dissipate the heat from the effluent. This allows the hot water or steam to transfer its heat energy to a cooling medium, effectively reducing its temperature. Once the effluent has been sufficiently cooled, it can then be safely discharged into the drainage system without posing a risk to the pipes.
  • The inclusion of a wastewater cooler in autoclaves is an important feature that helps protect the integrity of the drainage pipes. By preventing the direct discharge of hot water into the drainage system, the cooler system ensures the longevity and functionality of the pipes, reducing the need for costly repairs or replacements.

7. Control panel

  • All contemporary autoclaves are fitted with a controller interface similar to that of a microwave or oven. Nevertheless, autoclave control systems are typically more complex than those of domestic appliances.
  • A sterilisation cycle is governed by a preprogrammed software formula that sequentially opens and closes valves and other components.
  • Therefore, all autoclaves require a control system, whether it’s a “push button” system with a microprocessor or a programmable logic controller with a colour touch screen.

8. Thermostatic Trap

  • Every autoclave has a thermostatic trap or steam trap, a device that allows air and water (condensate) to leave the chamber.
  • Although a steam delivery system or steam autoclave may employ a variety of traps, they always serve the same fundamental purpose: eliminating condensate and restricting the passage of dry steam.
  • Typical steam traps are temperature-sensitive valves that close at a predetermined temperature. Thermostatic traps are essential to the construction of any autoclave.
autoclave diagram
autoclave diagram | Image Source:

Approximate Conditions for Autoclave sterilization

OrganismVegetative CellsSpores
Yeasts5 minutes at 50-60 degree centigrade.5 minutes at 70-80 degree centigrade.
Molds30 minutes at 62 degrees centigrade.30 minutes at 80 degrees centigrade.
Bacteria10 minutes at 60-70 degrees centigrade.2 to over 800 minutes at 100 degrees centigrade. 0.5 – 12 minutes at 121 degrees centigrade.
Viruses30 minutes at 60 degrees centigrade.

Autoclave Pressure and Temperature Chart

Steam autoclave121 C (250 F)15psi15min
unwrapped items132 C (270 F)30psi3min
lightly wrapped items132 C (270 F)30psi8min
heavily wrapped items132 C (270 F)30psi10min
Dry heat wrapped170 C (340 F)
160 C (340 F)
150 C (300F)
140 C (285F)
121 C (250F)
60 min
Dry heat (rapid flow) unwrapped items190 C (375F)6min
Dry heat (rapid flow) packaged items190 C (375 F)12min
Ethylene oxideAmbient8-10 hours
Chemical vapor132 C (270 F)20-40 psi20min

Operating Procedures of Autoclave

Operating an autoclave requires following a set of procedures to ensure proper sterilization. Here are the steps typically involved in operating an autoclave:

  1. Check the autoclave: Before starting a new cycle, inspect the autoclave chamber for any remaining items from the previous cycle. Ensure that the chamber is clean and ready for use.
  2. Add water: Add a sufficient amount of water to the autoclave chamber. The water level should be appropriate to generate the necessary steam for sterilization.
  3. Load the materials: Place the items or materials to be sterilized inside the autoclave chamber. Make sure they are arranged in a way that allows proper steam penetration and circulation.
  4. Close the lid: Close the autoclave lid securely and tighten the screws to create an airtight seal. This ensures that the sterilization process takes place in a controlled environment.
  5. Activate the electric heater: Switch on the electric heater to initiate the heating process. The electric heater will heat the water, generating steam inside the chamber.
  6. Adjust safety valves: Adjust the safety valves to maintain the required pressure inside the autoclave chamber. The pressure is typically set to at least 15 pounds per square inch (psi) or as per the specific sterilization requirements.
  7. Release air-water mixture: Once the water inside the chamber reaches boiling point, allow the air-water mixture to escape through the discharge tube. This displacement process ensures that all the air is expelled from the chamber.
  8. Close the drainage pipe: After the air-water mixture has been discharged, close the drainage pipe to contain the steam inside the chamber. The autoclave will continue to generate steam until the desired pressure is reached.
  9. Pressure release: When the autoclave reaches the desired pressure, the whistle or pressure relief valve will activate, releasing excess pressure from the chamber to maintain the required pressure level.
  10. Holding period: After the pressure release, the autoclave is typically operated for a specified holding period, usually around 15 minutes. This holding time allows sufficient exposure of the materials to the sterilizing conditions.
  11. Cooling phase: Once the holding period is complete, switch off the electric heater and allow the autoclave to cool. The autoclave should remain closed until the pressure gauge indicates that the pressure inside has dropped to atmospheric pressure.
  12. Open the discharge pipe: Open the discharge pipe to allow air from the outside to enter the autoclave, equalizing the pressure inside and outside the chamber.
  13. Open the lid: Finally, open the lid of the autoclave and carefully remove the sterilized materials from the chamber. Take necessary precautions to avoid burns or injuries during this process.

By following these operating procedures, the autoclave ensures proper sterilization of materials and maintains a safe and controlled environment for the sterilization process.

Air removal form Autoclave

Air removal from the autoclave is a crucial step to ensure effective sterilization. Trapped air can hinder the achievement of sterility, as it is a poor medium for sterilization compared to steam. There are several methods used for air removal in autoclaves:

  1. Downward Displacement (Gravity-Type): In this method, steam enters the chamber and fills the upper areas first, displacing the less dense air to the bottom. The compressed air is then forced out through a drain, often equipped with a temperature sensor. The discharge of air stops when the evacuation is complete. The flow is controlled by a steam trap, solenoid valve, or bleed holes. This process can also force out the steam-air mixture from locations in the chamber other than the bottom.
  2. Steam Pulsing: Air dilution is achieved by using a series of steam pulses. The chamber is alternately pressurized and then depressurized to near atmospheric pressure, allowing the steam to displace the air effectively.
  3. Vacuum Pumps: Vacuum pumps are used to suck out the air or air/steam mixtures from the autoclave chamber. This method creates a vacuum to remove the air before introducing steam for sterilization.
  4. Superatmospheric Cycles: These cycles involve a combination of vacuum and steam pulses achieved with a vacuum pump. The cycle starts with a vacuum, followed by a steam pulse, and then another vacuum, and so on. The number of pulses depends on the specific autoclave and sterilization cycle chosen.
  5. Subatmospheric Cycles: Similar to superatmospheric cycles, subatmospheric cycles also involve vacuum and steam pulses. However, in subatmospheric cycles, the chamber pressure never exceeds atmospheric pressure until it reaches the sterilizing temperature.

It’s important to note that in some stovetop autoclaves used in non-medical or poorer settings, automatic air removal programs may be lacking. In such cases, the operator must manually perform steam pulsing at specific pressures indicated by the gauge to facilitate air removal.

Proper air removal from the autoclave ensures that the sterilization process can be carried out effectively, providing reliable and safe sterilized equipment, instruments, or other items.

Compatible/incompatible materials for the autoclave – Which Materials You can Autoclave?

Autoclaves are versatile devices that can effectively sterilize a wide range of materials. However, it’s important to understand which materials are compatible with autoclaving and which should be avoided. Here are some materials that can be autoclaved and those that are incompatible:

Autoclave Compatible Materials:

  1. Glass: Only Pyrex® glass or Type I borosilicate glass can withstand autoclaving. When autoclaving liquids in Pyrex® containers, they should not be filled above two-thirds capacity and should not be sealed.
  2. Polypropylene: Polypropylene is a low-cost resin that is resistant to autoclave temperatures. Polypropylene containers are commonly used as secondary containers for autoclaved products.
  3. Stainless Steel: Most metals, including stainless steel, are suitable for autoclaving. However, ensure that any plastics, liners, or other materials that could melt or catch fire are removed before autoclaving.
  4. Pipette Tips: Many pipette tips, whether made of plastic or high-density polyethylene, are autoclavable. However, it is recommended to place pipette tips in the autoclave as waste within a biohazard bag and sterilize them using a steam-producing mode.
  5. Media Solutions: Liquids should not be autoclaved in sealed containers. Fill containers up to two-thirds capacity and remove the tops. Media solutions should be autoclaved using a cycle that generates steam.
  6. Tissue Culture Flasks, Litter, and Pet Food: These items are typically autoclave compatible and can be effectively sterilized.

Autoclave Incompatible Materials:

  1. Chlorine, Hypochlorite, Bleach: These chemicals are incompatible with autoclaving and should not be autoclaved.
  2. Acids, Bases, and Organic Solvents: Autoclaving these substances can be hazardous and should be avoided.
  3. Chlorides, Sulphates, Sea Water: These materials are not suitable for autoclaving and can cause damage to the autoclave.
  4. Polystyrene, Polyethylene, Polyurethane: Lab ware made of these materials should not be autoclaved as they can melt or deform.
Autoclave Compatible MaterialsAutoclave Incompatible Materials
PolypropyleneChlorine, Hypochlorite, Bleach
Glassware (Pyrex® or borosilicate)Acids, Bases, Organic Solvents
Stainless SteelChlorides, Sulphates, Sea Water
Pipette TipsPolystyrene, Polyethylene, Polyurethane
Media Solutions
Tissue Culture Flasks
Litter and Pet Food

Types of Autoclave

Types of Autoclave Based on size

Autoclaves can be classified into different types based on their size. Here are two common types of autoclaves based on size:

1. Large-scale autoclave

  • Large-scale autoclaves are characterized by their significant size and capacity. Some models may even feature double chambers. These autoclaves typically have a chamber capacity ranging from 500 liters to over 1500 liters, although the specific capacities may vary depending on the manufacturer. For example, companies like Systec offer large autoclaves with capacities ranging from 510 liters to 1580 liters.
  • Large-scale autoclaves are well-suited for use in hospitals, clinical settings, and research laboratories where a high volume of materials requires sterilization. Their larger size allows for the sterilization of a substantial amount of equipment, instruments, and other autoclavable items in a single cycle, improving efficiency and productivity.

2. Small-scale autoclave

  • Small-scale autoclaves, as the name suggests, are smaller in size compared to their large-scale counterparts. These autoclaves typically have chambers that can accommodate 20-300 liters of autoclavable materials simultaneously. However, the exact size range may vary depending on the manufacturer and specific model.
  • Small-scale autoclaves are commonly used in university and college laboratories, research facilities, and other settings where the volume of materials to be sterilized is relatively lower. These autoclaves offer a compact and efficient solution for sterilizing smaller quantities of equipment, glassware, media, and other laboratory supplies.

The choice between a large-scale and small-scale autoclave depends on the specific needs and requirements of the facility. Factors such as the volume of materials to be sterilized, available space, and budget considerations play a role in determining the appropriate size of the autoclave for a particular application.

Types of Autoclave Based of principle

Autoclaves can be categorized into different types based on the principle they operate on. Here are some common types of autoclaves based on their principle:

  1. Gravity displacement autoclave: In a gravity displacement autoclave, hot steam enters the chamber, displacing the air through a vent. This type of autoclave is typically not suitable for autoclave bags as it may create air pockets. Gravity displacement autoclaves can be further classified into two types:
    • Horizontal autoclave: In a horizontal autoclave, the door or lid opens outward towards the handler. This type of autoclave is usually available in larger sizes and is commonly used in industrial and healthcare settings.
    • Vertical autoclave: In a vertical autoclave, the autoclavable material is loaded from the top side of the autoclave. Vertical autoclaves are typically available in smaller sizes and are commonly used in laboratories and research facilities.
  2. Positive pressure displacement autoclave: In a positive pressure displacement autoclave, steam is generated in a separate steam generator unit and then transferred into the autoclave. This method is faster, as it takes only a few seconds to generate steam. Positive pressure displacement autoclaves are commonly used in industrial and medical applications where efficiency and speed are important.
  3. Negative pressure (vacuum) displacement autoclave: In a negative pressure displacement autoclave, a vacuum generator creates a vacuum inside the chamber before starting the sterilization cycle. This vacuum removes air from the chamber, ensuring more effective sterilization. Negative pressure displacement autoclaves typically have both a steam generator and a vacuum generator integrated into their design. They are often used in settings where thorough sterilization is critical, such as in healthcare facilities and laboratories.
Types of Autoclave Based of principle
Types of Autoclave Based of principle

The choice of autoclave type based on the principle depends on the specific requirements of the application, the nature of the materials to be sterilized, and the desired level of sterilization effectiveness. Each type has its advantages and considerations, and selecting the appropriate autoclave type is essential to ensure proper sterilization and safety.

Types of autoclave
Types of autoclave

Classes of autoclaves

When it comes to autoclaves, there are three main classes to choose from, each offering different features and capabilities.

  1. Class B Autoclaves: Class B autoclaves are considered the most advanced steam sterilizers available. These autoclaves have a separate steam generator that rapidly produces steam, which is then introduced into the autoclave chamber. One key feature of Class B autoclaves is the post-sterilization vacuum drying process. This ensures thorough and complete drying of all sterilized loads after the sterilization cycle is finished. Class B autoclaves are widely used in various settings such as hospitals, dental offices, laboratories, and tattoo studios. They comply with certification standards (such as NF EN13060) and meet the sanitary and epidemiological requirements necessary for sterilization.
  2. Class N Autoclaves: Class N autoclaves are the lowest class of autoclave devices. They are suitable for sterilizing instruments with a solid structure. However, they are not designed for sterilizing hollow or porous items or sterilizing items wrapped in packaging materials. Class N autoclaves are equipped with an air and steam vent valve. While they do not guarantee 100% air removal, they lack an effective drying option. These autoclaves are typically less complex and offer basic sterilization capabilities.
  3. Class S Autoclaves: Class S autoclaves represent an intermediate class between Class N and Class B. They allow for the sterilization of single-wrapped, multi-layered, and larger instruments that cannot be sterilized in Class N autoclaves. Autoclaves in Class S have a vacuum pump that facilitates the removal of air from the chamber prior to initiating the sterilization process. However, they are less efficient in air removal compared to Class B autoclaves. Class S autoclaves provide greater versatility and functionality than Class N autoclaves, making them suitable for a wider range of sterilization needs.

When selecting an autoclave, considering the specific requirements of the materials and instruments to be sterilized is crucial. Factors such as the nature of the items, desired level of air removal, and drying capabilities will help determine the appropriate class of autoclave to meet the sterilization needs effectively.


While operating an autoclave, it is important to follow certain precautions to ensure safety and effective sterilization. Here are some important precautions to consider:

  1. Avoid sterilizing water-proof or water-resistant substances: Autoclaves are not suitable for sterilizing substances like oils or powders that are not penetrable by steam. These substances may not achieve proper sterilization and can potentially damage the autoclave.
  2. Do not overcrowd the autoclave: Proper loading is crucial to ensure sufficient penetration of steam into the materials being sterilized. Avoid overcrowding the autoclave chamber, and arrange the items in a way that allows steam to reach all surfaces.
  3. Use secondary containers: When placing items inside the autoclave, it is recommended to use secondary containers to prevent direct contact with the chamber. This helps maintain cleanliness and facilitates easier handling of sterilized items.
  4. Use autoclavable bags for packaged waste: When autoclaving waste materials, use autoclavable bags designed for this purpose. These bags are specifically designed to withstand the sterilization process and ensure proper containment of the waste.
  5. Ensure proper wrapping materials: Use wrapping materials that allow penetration by steam, ensuring proper sterilization. Avoid using materials like aluminum foils that may impede steam penetration and affect the sterilization process.
  6. Avoid touching chamber walls: Items placed inside the autoclave should not touch the sides or top of the chamber. Leave sufficient space between the materials and the chamber walls to allow steam circulation.
  7. Separate clean and waste items: Keep clean and waste items separate during autoclaving. Autoclave them in separate cycles to avoid cross-contamination and ensure proper sterilization of clean items.
  8. Do not attempt to open the lid during operation: Opening the autoclave lid while it is running can be dangerous. Avoid any attempts to open the lid until the sterilization cycle is complete and the pressure has been released.
  9. Caution with liquid components: When autoclaving liquids, use containers that are not completely sealed to allow for pressure release. Do not fill the containers to their maximum capacity; leave room for expansion to prevent spillage or breakage.
  10. Avoid using plastic or polyethylene containers: Plastic or polyethylene trays or containers may melt under the high temperatures inside the autoclave. Choose appropriate autoclavable materials that can withstand the sterilization process.
  11. Do not autoclave hazardous materials: Never autoclave flammable, reactive, corrosive, toxic, or radioactive materials. These substances can pose serious risks during the sterilization process and may damage the autoclave.
  12. Handle paper with care: Paper is a combustible material and should not be placed directly inside an autoclave. If paper needs to be sterilized, use a waste bag or a bio bag setting specifically designed for paper to prevent the risk of fire.

By following these precautions, you can ensure the safe and effective operation of an autoclave, minimizing risks and achieving reliable sterilization results. Always refer to the manufacturer’s guidelines and protocols for your specific autoclave model.

Sterilization control/Quality Control of Autoclave/Validation of Autoclave

Modern autoclaves come with equipment to keep the pressure at a constant level and to record internal temperature throughout the operation. No matter the presence of such a device the pressure of the autoclave should be monitored frequently and kept at a constant level.

There are a variety of methods available to make sure that autoclaves ensures the goal of sterility. The efficiency of sterilization process that is performed by the autoclave can be monitored through:

1. Biological indicator

  • A biological indicator, also known as a biological spore test or spore strip, is a method used to verify the effectiveness of sterilization processes, particularly in autoclaves. It involves the use of highly resistant bacterial spores to assess whether the autoclave has successfully destroyed the microorganisms.
  • One of the most commonly used biological indicators is the spores of Geobacillus stearothermophilus (formerly known as Bacillus stearothermophilus). These spores are highly resistant to steam and serve as a reliable indicator of autoclave performance. They can withstand high temperatures and require a specific time and temperature combination for complete destruction.
  • The Centers for Disease Control (CDC) recommends performing a weekly autoclaving test using a culture containing heat-resistant endospores of Geobacillus stearothermophilus to assess the autoclave’s effectiveness. Commercially available spore strips typically consist of a soft plastic vial containing an ampule of growth medium and spores.
  • During the test, the spore strip is placed in the center of the load or material to be sterilized within the autoclave. The autoclave cycle is then initiated, subjecting the spores to the specified time and temperature parameters. After the cycle, the inner ampule of the vial is broken, releasing the growth medium.
  • The entire container, including the spore strip and medium, is then incubated under appropriate conditions. If no growth is observed in the culture after incubation, it indicates that the autoclave has effectively sterilized the load, and the process is deemed successful. The absence of bacterial growth confirms that the autoclave’s parameters, including temperature and duration, were sufficient to destroy the highly resistant Geobacillus stearothermophilus spores.
  • Biological indicators provide a valuable quality control measure, ensuring the reliability and consistency of autoclave sterilization. They offer a more rigorous assessment than solely relying on physical indicators, such as temperature and pressure gauges, by directly assessing the destruction of microbial life.
  • By regularly conducting biological indicator tests, healthcare facilities, laboratories, and other settings can validate the efficacy of their autoclave processes and maintain a high standard of sterilization to prevent the spread of infectious agents.
Quality Control of Autoclave
Quality Control of Autoclave

By following this procedure and conducting regular biological indicator tests, laboratories can ensure the effectiveness of their autoclaves in treating biological waste and maintaining a safe working environment.

2. Autoclave tapes

  • Autoclave tapes are adhesive-backed paper tapes that are used as a visual indicator to check the effectiveness of autoclaves in achieving sterilization. These tapes contain a heat-sensitive, chemical indicator that undergoes a color change or displays specific markings when exposed to the proper sterilization temperature, typically 121°C.
  • The purpose of autoclave tapes is to provide a quick visual confirmation that the package or load has been subjected to the appropriate temperature during the sterilization process. The color change or display of diagonal stripes, the words “sterile,” or “autoclaved” on the tape indicate that it has been exposed to the effective sterilization temperature.
  • To ensure proper heat penetration and sterilization, the tapes are placed inside the autoclave and near the center of large packages or loads. Heat penetration is critical to achieving sterilization throughout the entire load, similar to ensuring that the center of a large piece of meat is cooked thoroughly. By placing the tapes in these areas, it can be inferred that if the tape shows the appropriate color change or markings, then adequate heat penetration has likely occurred.
  • It’s important to note that autoclave tapes have limitations. They do not provide information about how long the appropriate sterilization conditions were maintained. They only serve as a visual indicator that the temperature threshold has been reached. Other factors such as pressure, duration, and steam quality, which are crucial for effective sterilization, are not indicated by the tape.
  • While autoclave tapes can provide a quick and convenient visual cue, they should not be solely relied upon to validate the sterilization process. Additional monitoring methods, such as biological indicators, should be used to verify the effectiveness of the autoclave and ensure proper sterilization of the materials or instruments.
  • In summary, autoclave tapes with heat-sensitive, chemical indicators are adhesive-backed paper tapes used as visual indicators to confirm exposure to the appropriate sterilization temperature. They are placed inside or near the center of packages or loads to indicate heat penetration. However, they do not provide information on the duration or other critical sterilization parameters, making them an auxiliary tool rather than a comprehensive validation method for autoclave sterilization.

3. Other useful indicators are thermocouple and Browne’s tube.

  • In addition to autoclave tapes, other useful indicators used in sterilization processes are thermocouples and Browne’s tubes.
  • A thermocouple is a temperature measuring device that consists of two different metal wires joined together at one end. When exposed to heat, a voltage is generated at the junction of the wires, which is proportional to the temperature. This voltage is then measured by a potentiometer or temperature measuring device, providing an accurate temperature reading. Thermocouples are commonly used in various industries, including healthcare, research, and manufacturing, to monitor and record temperature profiles during sterilization processes. They offer real-time temperature data and are valuable tools for ensuring the desired sterilization temperature is achieved and maintained.
  • Browne’s tube, invented by Albert Browne in 1930, is another type of indicator used to monitor sterilization conditions. It consists of a glass tube filled with a heat-sensitive red dye. When exposed to a specific temperature for a defined period of time, the dye undergoes a color change, turning from red to green. The conversion of dye color provides information about both the duration of time and the temperature to which it was exposed. Browne’s tubes are useful for assessing the adequacy of the sterilization process, as they indicate if the desired temperature and exposure time have been reached. They can be used as a visual confirmation of proper sterilization conditions.
  • Both thermocouples and Browne’s tubes offer additional information beyond the basic temperature change provided by autoclave tapes. Thermocouples provide precise temperature measurements, allowing for accurate monitoring and control of the sterilization process. Browne’s tubes, on the other hand, provide a visual indication of both temperature and time, giving insight into the duration of exposure at a specific temperature.
  • These indicators serve as valuable tools for quality control and validation in sterilization processes. They help ensure that the desired temperature and exposure time are met, providing confidence in the effectiveness of the sterilization process. By using thermocouples and Browne’s tubes alongside autoclave tapes and other monitoring methods, professionals can obtain more comprehensive data and enhance the reliability of the sterilization process.

What is Autoclave Cycle?

Autoclave cycles refer to the specific settings and conditions used during the sterilization process in an autoclave. The choice of cycle depends on the type of load being sterilized and its characteristics. Here are some common autoclave cycles:

  1. Liquids Cycle: This cycle is suitable for sterilizing liquid materials. It requires the use of glass containers with vented lids filled only up to two-thirds of their capacity. The liquids that can be sterilized include liquid media, non-flammable liquids, liquid organic waste, aqueous solutions, and similar substances. The cycle typically involves a slower exhaust to prevent overheating and boiling over of the liquids.
  2. Solids or Dry Cycle: This cycle is designed for sterilizing solid or dry materials. It is suitable for unwrapped or porous-packaged dry goods, metals, non-porous substances, and items like empty wine glasses. Unlike the liquids cycle, a rapid exhaust cycle can be used for this cycle since there is no risk of boiling over.
  3. Wrapped Goods or Pre-vacuum Cycle: This cycle is used for sterilizing wrapped items or those that require pre-vacuum conditions. It is commonly used for packaging such as pipette tip packaging and biohazardous waste contained in autoclave bags. Sterile glassware that needs to be sterilized vertically is also suitable for this cycle. The pre-vacuum cycle helps to remove air from the chamber before introducing steam, ensuring effective sterilization of wrapped items.
  4. Sharps Disinfection: This cycle is specifically designed for the disinfection of sharps, such as needles and scalpels. It ensures the complete sterilization of these items, reducing the risk of infection transmission.

It’s important to note that the specific settings and durations of these autoclave cycles may vary depending on the manufacturer and the specific autoclave model. The recommended temperature for effective sterilization is 121°C, and the cycle should maintain this temperature for at least 30 minutes with saturated steam at a pressure of at least 15 psi. However, depending on the composition and size of the load, longer cycle times may be required to ensure proper sterilization. It is essential to follow the manufacturer’s guidelines and instructions for the appropriate cycle selection and operation of the autoclave to achieve effective sterilization results.

Safety Tips to Observe When Using the Autoclave Sterilizer

When using an autoclave sterilizer, it’s important to prioritize safety. Here are some essential safety tips to observe:

  1. Training: Ensure that laboratory personnel are properly trained before using a specific model of autoclave. Familiarize yourself with the operating procedures and safety guidelines.
  2. Avoid Overcrowding: Do not overcrowd the autoclave chamber. Leave enough space between items to allow for efficient sterilization.
  3. Secondary Chamber: Place the items to be autoclaved in a secondary container. This helps prevent any potential contamination and aids in the sterilization process.
  4. Autoclavable Bags: Only use autoclavable bags for packaging and autoclaving materials or waste. These bags are designed to withstand the sterilization process.
  5. Steam Penetration: Wrap the materials in a way that promotes steam penetration. Avoid using aluminum foil, as it may hinder proper steam circulation.
  6. Chamber Contact: Ensure that the items inside the chamber do not touch the sides or top of the chamber. Proper spacing allows for even sterilization.
  7. Lid Safety: Never attempt to open the autoclave’s lid while it is running. Wait for the pressure to be fully released before accessing the contents.
  8. Separate Clean and Waste Material: Autoclave clean and waste materials separately to avoid any cross-contamination.
  9. Liquid Containment: Do not fill liquid-containing vessels more than two-thirds of their total volume to prevent spillage during the sterilization process.
  10. Sealed Containers: Do not autoclave liquid components in sealed containers. The pressure build-up can cause explosions. Ensure proper venting.
  11. Pre-Heating Check: Before pre-heating the autoclave, check for any previous items left inside to prevent any hazards.
  12. Water Level: Always check the water level of the autoclave before starting the sterilization process. Insufficient water can damage the machine.
  13. Secure Lids: Close the autoclave lids tightly and ensure the screws are tightened properly before switching on the electric heater.
  14. Post-Sterilization Cooling: After sterilization, do not open the autoclave or attempt to touch the materials immediately. Allow them to cool down first.
  15. Avoid Sealing Autoclavable Items: Do not seal any items meant to be autoclaved, as it can create an explosion hazard.
  16. Positioning: Never stand directly in front of the autoclave door. Keep a safe distance during operation.
  17. Maintenance and Reporting: Perform routine maintenance on the autoclave and regularly check its operations. Report any malfunctions, such as leaking valves, temperature fluctuations, or gasket deterioration, to the appropriate authority.

By adhering to these safety tips, you can ensure a safe and effective autoclave sterilization process in your laboratory or facility.

Uses of Autoclave

Autoclaves are versatile devices that find various uses in different settings. Some common applications of autoclaves include:

  1. Medical facilities: Autoclaves play a crucial role in medical facilities for sterilizing medical instruments, including surgical tools, syringes, and other reusable equipment. They are also used to sterilize materials such as dressings, bandages, and linens.
  2. Dental offices: Autoclaves are essential in dental offices to sterilize dental instruments like drills, forceps, and probes. This ensures a safe and sterile environment for dental procedures.
  3. Laboratories: Autoclaves are extensively used in research laboratories, microbiology labs, and biotechnology labs for sterilizing laboratory glassware, pipettes, media, Petri dishes, and other equipment. It helps prevent contamination and maintain the integrity of experiments and cultures.
  4. Pharmaceutical industry: Autoclaves are employed in the pharmaceutical industry to sterilize equipment, vials, containers, and packaging materials. This ensures the safety and sterility of pharmaceutical products.
  5. Veterinary clinics: Autoclaves are used in veterinary clinics and animal research facilities for sterilizing surgical instruments, lab equipment, and animal care supplies. This helps prevent the spread of infections and ensures the well-being of animals.
  6. Food processing facilities: Autoclaves find application in the food industry to sterilize containers, packaging materials, and equipment used in food processing. This helps maintain food safety and extends the shelf life of products.
  7. Waste management: Autoclaves are used to treat and sterilize regulated medical waste, such as contaminated gloves, gowns, and other biomedical waste, before disposal. This ensures the safe handling and disposal of potentially infectious materials.

Autoclaves are essential in environments where sterility is paramount. They provide a reliable method of sterilization, eliminating harmful microorganisms and reducing the risk of contamination. Proper usage and adherence to sterilization protocols are crucial to ensure effective sterilization and maintain a safe working environment.

Advantages of Autoclave

Autoclaves offer several advantages in the process of sterilization. Here are some key benefits:

  1. High efficiency: Autoclaves are known for their high efficiency in sterilizing materials and equipment. The combination of high temperatures and pressure generated by steam effectively kills microorganisms, including bacteria, fungi, and spores.
  2. Versatility: Autoclaves can sterilize a wide range of materials, making them suitable for various applications. Whether it’s metal, glass, plastic, or other heat-resistant materials, autoclaves can effectively sterilize them.
  3. Ease of use: Autoclaves are designed to be user-friendly, with control panels that allow operators to set the desired temperature, pressure, and sterilization time. Once the parameters are set, the autoclave operates automatically, requiring minimal manual intervention.
  4. Safety: When operated properly and following manufacturer’s instructions, autoclaves are considered safe. They are equipped with safety features to prevent mishaps and ensure operator protection during the sterilization process.
  5. Cost-effective: Autoclaves are economical in the long run. They eliminate the need for additional chemicals or disposable items, reducing ongoing costs associated with sterilization. Once purchased, autoclaves offer a reliable and cost-effective solution for sterilizing a variety of materials.
  6. Time-efficient: Autoclaves offer shorter procedure times compared to alternative sterilization methods, such as dry heat. The combination of high temperature and pressure allows for rapid and efficient sterilization, saving time in busy healthcare or laboratory settings.
  7. Effective penetration: The steam generated in autoclaves provides excellent penetration into all surfaces of the materials being sterilized. This ensures thorough sterilization, even in complex or hard-to-reach areas.
  8. Large capacity: Autoclaves come in different sizes, including larger models capable of sterilizing a significant quantity of materials in a single batch. This makes them suitable for high-volume sterilization needs in hospitals, research laboratories, and industrial settings.

In summary, autoclaves offer advantages such as high efficiency, versatility, ease of use, safety, cost-effectiveness, shorter procedure times, effective penetration, and the ability to sterilize large quantities of materials. These features make autoclaves a preferred choice for sterilization processes in various industries.

Disadvantages of Autoclave

Autoclaves, despite their advantages, have some disadvantages that should be considered. Here are some key drawbacks:

  1. Moisture retention: Autoclaves use steam for sterilization, which can result in moisture retention within the sterilized materials. This can be problematic for certain items, such as sensitive electronics or heat-sensitive substances that may be damaged or altered by moisture.
  2. Compatibility limitations: Autoclaves are suitable for sterilizing materials made of stainless steel and heat-resistant plastics. However, they may not be suitable for heat-labile substances that cannot withstand the high temperatures and pressure of the autoclave process. Additionally, certain materials such as powders and oils may not be effectively sterilized using an autoclave.
  3. Cost: Autoclaves can be expensive to purchase and maintain, especially larger or more advanced models. The initial investment and ongoing costs associated with maintenance, calibration, and regular servicing should be considered.
  4. Size and weight: Autoclaves are typically large and heavy equipment, which may pose challenges in terms of space requirements and transportation. The size and weight of autoclaves can limit their use in certain settings or require dedicated space and infrastructure.
  5. Risk of injury: Improper use of an autoclave can pose risks of injury to operators. The high temperatures, pressure, and steam involved in the sterilization process can cause burns or cuts if safety precautions are not followed strictly.
  6. Limited material compatibility: Autoclaves may not be suitable for sterilizing certain materials, such as sharp instruments or flammable substances. Sharp instruments can dull or become damaged during the autoclave cycle, and flammable materials can pose a fire hazard.

It’s important to consider these disadvantages and evaluate the specific needs and requirements of the sterilization process when deciding on the appropriate method or equipment to use. Alternative sterilization methods may be more suitable for certain materials or situations where autoclaves have limitations.

Examples of Autoclave

Tuttnauer autoclave

Tuttnauer is a manufacturer of autoclaves and other sterilization equipment. Tuttnauer autoclaves are used in a variety of settings, including hospitals, dental offices, laboratories, and research facilities, to sterilize a wide range of materials.

Tuttnauer autoclaves use steam under pressure to sterilize materials, and the temperature of the steam can reach 121-134°C (250-273°F). This high temperature is necessary to kill all types of microorganisms, including spores of thermophilic bacteria, which are resistant to lower temperatures.

Tuttnauer autoclaves are available in a range of sizes and models to suit the needs of different users. Some models are designed for use in small laboratories or dental offices, while others are larger and suitable for use in hospitals or research facilities.

Tuttnauer autoclaves are known for their reliability and durability, and the company offers a range of maintenance and repair services to ensure that their autoclaves are operating at optimal performance.

Midmark autoclave

Midmark is a manufacturer of medical and dental equipment, including autoclaves. Midmark autoclaves are used to sterilize a wide range of materials, including medical instruments, laboratory glassware, and textiles.

Midmark autoclaves use steam under pressure to sterilize materials, and the temperature of the steam can reach 121-134°C (250-273°F). This high temperature is necessary to kill all types of microorganisms, including spores of thermophilic bacteria, which are resistant to lower temperatures.

Midmark autoclaves are available in a range of sizes and models to suit the needs of different users. Some models are designed for use in small laboratories or dental offices, while others are larger and suitable for use in hospitals or research facilities.

Midmark autoclaves are known for their reliability and durability, and the company offers a range of maintenance and repair services to ensure that their autoclaves are operating at optimal performance.

FAQ on Autoclave

1. What are autoclave bags made of?

Autoclave bags made of two-millimeter-thick Polypropylene (PP).

2. Why are autoclave indicators used?

Autoclave indicators are used to make sure that articles have been sterilized. Autoclave tape, sensitivity marks on bags or wraps, and indicator capsules.

3. What are autoclave bags used for?

Autoclave bags are used in high heat sterilization applications in order to prevent low temp plastics inside the bag from sticking to the walls of the sterilizer

4. Can autoclave kill endospores?

Yes, By increasing the pressure, the autoclave reaches a boiling point of 100°C or higher (121°C) and kills endospores.

5. Can autoclave kill prions?

Yes, by exposing them to effective sterilisation temperatures for around 14 minutes longer than the standard 134°C cycle.

6. How autoclave kill microorganisms?

Autoclaves kill microorganisms by degrading nucleic acids and denaturing enzymes and other essential proteins.

how does an autoclave work

To sterilise items, autoclaves employ tremendous heat in the form of pressurised steam. An autoclave, like a pressure cooker, uses a locked door to produce a sealed chamber. The air within the chamber is then replenished with pressured steam until the goods within the chamber are adequately disinfected.

How does autoclaving kill bacteria?

Using steam heat, autoclaves elevate temperatures to the point where proteins within the cell walls of a microbe begin to denature and coagulate, resulting in the bacterium’s death and sterilisation.

Why is autoclaving items better for sterilization purposes than boiling them?

Autoclaves are more effective at sterilization than boiling because they use higher temperatures and pressures. Autoclaves use steam under pressure to sterilize materials, and the temperature of the steam can reach 121-134°C (250-273°F). This high temperature is necessary to kill all types of microorganisms, including spores of thermophilic bacteria, which are resistant to lower temperatures.
In contrast, boiling water only reaches a maximum temperature of 100°C (212°F), which is not sufficient to kill all types of microorganisms. Boiling is effective at killing most bacteria and viruses, but it is not effective at killing spores and certain types of fungi.
Additionally, autoclaves use a combination of heat and pressure to sterilize materials, which can be more effective at killing microorganisms than heat alone. The pressure inside an autoclave can reach 15 pounds per square inch (psi), which helps to kill microorganisms that may be resistant to high temperatures.
Overall, autoclaves are a more effective method of sterilization than boiling because they use higher temperatures and pressures to kill a wider range of microorganisms.

How long does it take an autoclave to sterilize goods?

The time it takes for an autoclave to sterilize goods depends on several factors, including the size and type of material being sterilized, the type of autoclave being used, and the sterilization cycle being used.
In general, autoclaves use one of two types of sterilization cycles: a gravity cycle or a pre-vacuum cycle. The gravity cycle is typically faster than the pre-vacuum cycle, as it does not require the removal of air from the autoclave chamber before sterilization. However, the pre-vacuum cycle is generally more effective at sterilization because it removes air from the chamber, which allows steam to penetrate materials more effectively.
The size and type of material being sterilized also affect the sterilization time. Larger items or items with complex shapes may take longer to sterilize because they have more surface area that needs to be exposed to steam. Similarly, materials with a high moisture content, such as liquids or wet fabrics, may take longer to sterilize than dry materials.
In general, sterilization times for an autoclave range from 30 minutes to several hours, depending on the factors mentioned above. It is important to carefully follow the manufacturer’s instructions and guidelines for the specific autoclave being used to ensure that the materials are adequately sterilized.

What temperature(s) can an autoclave reach?

Autoclaves use steam under pressure to sterilize materials, and the temperature of the steam can reach 121-134°C (250-273°F). This high temperature is necessary to kill all types of microorganisms, including spores of thermophilic bacteria, which are resistant to lower temperatures.
The temperature inside an autoclave is controlled by the pressure of the steam, with higher pressures resulting in higher temperatures. The pressure inside an autoclave can reach 15 pounds per square inch (psi), which helps to kill microorganisms that may be resistant to high temperatures.
It is important to note that the temperature inside an autoclave may not be uniform throughout the chamber. The temperature may be higher near the steam source and lower in other areas of the chamber. As a result, it is important to carefully follow the manufacturer’s instructions and guidelines for the specific autoclave being used to ensure that all materials are adequately sterilized.

How long do items stay sterile after autoclaving?

Autoclaved items will remain sterile as long as they are kept in a sterile environment and are not contaminated by microorganisms.
After autoclaving, it is important to handle the items carefully to avoid contamination. This may involve wearing sterile gloves and using sterile techniques to transfer the items to a sterile container or storage area.
The length of time that autoclaved items will remain sterile will also depend on the type of material being sterilized and the storage conditions. Some materials, such as metal instruments, may remain sterile for an extended period of time if they are stored in a dry, sterile environment. Other materials, such as biological cultures or tissue samples, may be more susceptible to contamination and may need to be used or stored under more stringent conditions.
Overall, it is important to carefully consider the type of material being sterilized and the storage conditions to ensure that autoclaved items remain sterile for as long as needed.

Further Reading


  • (ANSI) American National Standards Institute Inc./(AAMI) Association for the Advancement of Medical Instrumentation

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