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

An autoclave is a vital tool in scientific and medical laboratories, essential for ensuring the sterility of equipment and materials. Understanding its definition, principle of operation, key components, and operating procedures is crucial for students in these fields. This post delves into what an autoclave is, how it works, its main parts, and its diverse applications. By exploring these aspects, students will gain valuable insights into how this powerful device contributes to maintaining a clean and safe environment in various scientific and healthcare settings.

What is an autoclave?

• An autoclave is a crucial instrument in various scientific and medical settings, designed to sterilize equipment and materials through the application of steam under high pressure. This process effectively eradicates a wide range of microorganisms, including bacteria, viruses, and even bacterial spores.
• The core principle behind autoclave sterilization involves the use of moist heat to achieve a high temperature, typically around 121°C (250°F), under increased pressure. The pressurized steam penetrates the materials and raises their temperature to levels that are lethal to most microbial life forms. Therefore, this method ensures that all contaminants are destroyed, far exceeding the effectiveness of simple washing with soap and water.
• Autoclaves operate by sealing the contents within a chamber and then subjecting them to steam at pressures usually ranging from 15 to 30 pounds per square inch (psi). The combination of heat and pressure ensures that even the most resilient spores are eliminated, making it a preferred method for sterilizing laboratory glassware, surgical instruments, and other heat-resistant equipment.
• In laboratory environments, particularly those handling pathogenic microorganisms, autoclaves are indispensable. They offer a reliable solution for achieving sterilization beyond the capabilities of conventional methods. The sterilization cycle typically includes a heating phase, a period of maintaining the temperature and pressure, and a cooling phase before the chamber is depressurized and opened.
• By using an autoclave, laboratories and healthcare facilities ensure that all equipment and materials are free from potentially harmful microorganisms, thus maintaining a sterile environment essential for safe and accurate scientific research and medical procedures.

Definition of Autoclave

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

Autoclave Pressure and Temperature Chart

STERILIZER	TEMPERATURE	PRESSURE	TIME
Steam autoclave	121°C (250°F)	15 psi	15 min
Unwrapped items	132°C (270°F)	30 psi	3 min
Lightly wrapped items	132°C (270°F)	30 psi	8 min
Heavily wrapped items	132°C (270°F)	30 psi	10 min
Dry heat wrapped	170°C (340°F)	–	60 min
160°C (340°F)	–	120 min
150°C (300°F)	–	150 min
140°C (285°F)	–	180 min
121°C (250°F)	–	12 hrs
Dry heat (rapid flow) unwrapped items	190°C (375°F)	–	6 min
Dry heat (rapid flow) packaged items	190°C (375°F)	–	12 min
Chemical vapor	132°C (270°F)	20-40 psi	20 min
Ethylene oxide	Ambient	8-10 hours

Principle of an Autoclave – How an Autoclave Works?

• The principle behind an autoclave centers on the use of moist heat to achieve effective sterilization. This process involves steam at high pressure to elevate the boiling point of water, allowing for temperatures above 100°C. As a result, materials inside the autoclave are exposed to steam at around 121°C under 15 psi (pounds per square inch) of pressure, which is critical for achieving sterilization.
• Under normal atmospheric conditions, water boils at 100°C. However, in an autoclave, increasing the pressure raises the boiling point of water, enabling the steam to reach higher temperatures. This enhanced temperature facilitates the rapid and deep penetration of heat into materials, ensuring that even heat-resistant microbial spores are effectively destroyed. The steam’s latent heat, when it condenses on cooler surfaces, transfers additional energy, aiding in the thorough killing of microorganisms.
• Moist heat sterilization works by causing the coagulation of proteins within microbes. This process irreversibly damages the microorganisms’ cellular structures, leading to their death. The high-pressure steam fills the autoclave chamber, ensuring that all surfaces and materials are uniformly exposed to the steam. This steam not only heats the materials but also penetrates deeply, ensuring comprehensive sterilization.
• After the sterilization phase, the pressure inside the chamber is gradually released. This is typically done through a pressure-regulating mechanism, which lowers the pressure back to ambient levels. As the pressure decreases, the steam condenses, and the temperature of the materials inside begins to decrease. It is crucial that the materials remain at the sterilization temperature for a sufficient period, usually 15-20 minutes, to ensure complete sterilization, especially for larger volumes or bulky items.
• Therefore, the effectiveness of an autoclave hinges on its ability to maintain high temperatures under pressure, coupled with thorough steam penetration, to ensure that all microbial life, including spores, is eradicated.

Autoclave Parts/ Components

An autoclave comprises several key components, each playing a crucial role in its operation and effectiveness. Understanding these parts is essential for proper use and maintenance of the device.

1. Pressure Chamber
   • Inner Chamber: This is where the materials to be sterilized are placed. It is typically constructed from stainless steel or gunmetal, designed to withstand high pressure and temperatures.
   • Outer Jacket: Surrounding the inner chamber, the outer jacket is often made of an iron case and is filled with steam. This design helps expedite the heating process and maintain the required sterilization temperature.
2. Lid/Door
   • Sealing Mechanism: The lid ensures an airtight seal to create a controlled environment inside the autoclave. It is secured with screw clamps and often includes an asbestos washer for a tight fit.
   • Pressure Gauge: Located on the lid, the pressure gauge monitors the internal pressure, ensuring the autoclave operates safely and effectively.
   • Pressure Releasing Unit/Whistle: This component controls the pressure by releasing steam when necessary, preventing excessive pressure buildup.
   • Safety Valve: A critical safety feature, the valve has a rubber layer that bursts under extreme pressure to prevent accidents and potential explosions.
3. Steam Generator/Electrical Heater
   • Steam Generation: Positioned beneath the chamber, this component heats water to produce steam. Proper water levels are crucial to avoid overheating or inefficient steam production.
   • Heating System: The electric heater ensures that the water reaches and maintains the temperature required for effective sterilization.
4. Vacuum Generator (if applicable)
   • Air Removal: Some autoclaves include a vacuum generator to remove air from the chamber. This step is essential to prevent air pockets that could harbor microorganisms, ensuring complete steam penetration.
5. Wastewater Cooler
   • Cooling System: This system cools the effluent before it exits the autoclave, preventing damage to drainage pipes from hot water. It helps maintain the longevity of the autoclave and associated plumbing.
6. Additional Components
   • Control Panel: Located beside the main switch, this panel controls the temperature and pressure settings within the autoclave.
   • Water Level Indicator: Displays the water level in the chamber to ensure that the correct amount is maintained for efficient operation.
   • Thermometer: Shows the internal temperature, providing essential feedback to ensure that sterilization conditions are met.
7. Accessories
   • Autoclave Bags: Used for placing waste materials to be sterilized, these bags ensure proper containment during the process.
   • Autoclave Baskets: These help transfer materials into and out of the autoclave safely. They come in various sizes and designs to accommodate different types of items.
   • Sterilization Boxes: Stainless steel boxes with lids and vents used to organize and sterilize materials within the chamber.

Autoclave Parts Summery Table

Component	Description
Lid/Door	Positioned at the top (or front in some cases) of the autoclave, it forms an airtight seal to prevent contamination and enable proper sterilization.
Pressure Chamber	The central vessel made of stainless steel, it houses the materials for sterilization and is tightly sealed by the lid.
Power Switch	Located on the side of the autoclave, it controls the electrical supply to the device.
Control Panel	Adjacent to the main switch, it regulates pressure and temperature within the autoclave for precise sterilization conditions.
Water Level Indicator	Monitors and displays the water level inside the autoclave, crucial for proper operation.
Pressure Gauge	Positioned on the lid, it indicates the pressure within the chamber, ensuring safety and functionality.
Whistle (Some Types)	Present in specific autoclave models, it releases excess pressure before opening the lid following sterilization.
Safety Valve	Located on the lid, it releases pressure in case of uncontrollable pressure build-up, preventing accidents.
Electrical Heater	The heating element beneath the chamber that generates steam by heating water.
Water Releasing Valve	Facilitates water removal for replacement and cleaning inside the autoclave chamber.
Thermometer	Positioned on the lid, it displays the chamber’s temperature during operation.
Stand	Provides stability and support, ensuring the autoclave remains upright.
Steam Generator/Electrical Heater (cont.)	Underneath the chamber, it heats water to generate steam within both the inner and outer chambers.
Vacuum Generator (if applicable)	In some autoclaves, it creates a vacuum by extracting air from the chamber, crucial for eliminating air pockets supporting microorganism growth.
Wastewater Cooler	Many autoclaves feature this system to cool the effluent before it enters drainage pipes, preventing damage due to boiling water discharge.

Approximate Conditions for Autoclave sterilization

Organism	Vegetative Cells	Spores
Yeasts	5 minutes at 50-60 degree centigrade.	5 minutes at 70-80 degree centigrade.
Molds	30 minutes at 62 degrees centigrade.	30 minutes at 80 degrees centigrade.
Bacteria	10 minutes at 60-70 degrees centigrade.	2 to over 800 minutes at 100 degrees centigrade. 0.5 – 12 minutes at 121 degrees centigrade.
Viruses	30 minutes at 60 degrees centigrade.

Operating Procedures of Autoclave – How to Use an Autoclave?

The autoclave operates through a series of carefully controlled steps to ensure effective sterilization of materials. Below is a detailed procedure for running an autoclave, emphasizing the key components and their functions throughout the process.

1. Preparation
   • Inspection: Before starting a new cycle, check the autoclave for any leftover items from the previous run. Ensure the chamber is clean and free of any residual materials.
   • Water Addition: Add a sufficient amount of water into the chamber. This water is crucial for generating steam, which is the primary agent for sterilization.
2. Loading Materials
   • Placement: Load the materials that need to be sterilized into the chamber. Ensure that items are properly arranged to allow steam to circulate effectively. For certain materials, such as specific glassware, wrapping with sterilization paper may be necessary.
3. Sealing and Heating
   • Lid Closure: Close the lid of the autoclave and secure it using screw clamps to ensure an airtight seal. This prevents any steam from escaping during the cycle.
   • Heating: Activate the electric heater to begin the heating process. This will start generating steam, which is essential for reaching the required sterilization temperature.
4. Pressure and Steam Management
   • Safety Valve Adjustment: Adjust the safety valve to maintain the necessary pressure inside the chamber. The standard pressure is typically 15 psi, which corresponds to a temperature of 121°C.
   • Air Displacement: As the water boils, allow the steam-air mixture to escape through the discharge pipe. This step is crucial to remove air from the chamber, as residual air can hinder effective sterilization. Confirm complete air displacement when air bubbles cease to appear in the discharge stream.
5. Sterilization Phase
   • Pressure Establishment: Close the discharge pipe once air displacement is complete. Allow the steam pressure to rise to the set level. The autoclave will now maintain this pressure to facilitate the sterilization process.
   • Holding Time: The sterilization phase typically lasts for 15 minutes. During this time, the high temperature and pressure will effectively destroy microorganisms present in the materials.
6. Cooling and Pressure Release
   • Heater Shutdown: After the holding period, turn off the electric heater. Allow the autoclave to cool naturally. The pressure gauge should show that the pressure inside has returned to atmospheric levels before proceeding.
   • Air Intake: Open the discharge pipe slowly to allow air to re-enter the chamber. This step helps to normalize the pressure and prepare the autoclave for safe opening.
7. Completion
   • Lid Opening: Once the pressure is equalized and the chamber has cooled down sufficiently, open the lid.
   • Material Removal: Carefully remove the sterilized materials from the chamber. Ensure that they are handled with sterile equipment or gloves to maintain their sterility.

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 Materials	Autoclave Incompatible Materials
Polypropylene	Chlorine, Hypochlorite, Bleach
Glassware (Pyrex® or borosilicate)	Acids, Bases, Organic Solvents
Stainless Steel	Chlorides, Sulphates, Sea Water
Pipette Tips	Polystyrene, Polyethylene, Polyurethane
Waste
Media Solutions
Tissue Culture Flasks
Litter and Pet Food

Types of Autoclave

Autoclaves are critical in various fields for ensuring sterilization through high-pressure steam. They come in different types, each suited to specific needs based on their design and operational principles. Below is an overview of the main types of autoclaves, emphasizing their unique characteristics and applications.

1. Pressure Cooker Type (Laboratory Bench Autoclaves)
   • Description: This type resembles domestic pressure cookers but is designed for laboratory use. It includes a metal chamber with a secure lid, sealed with a rubber gasket.
   • Components:
     • Air and Steam Discharge Tap: Allows for the release of air and steam.
     • Pressure Gauge: Monitors the pressure within the chamber.
     • Safety Valve: Prevents excessive pressure buildup.
     • Electric Immersion Heater: Located at the bottom of the chamber, heats the water to generate steam.
   • Applications: Often used in settings where basic sterilization is required.
2. Gravity Displacement Autoclave
   • Description: Commonly used in laboratories, this autoclave relies on gravity to displace air and facilitate steam penetration.
   • Operational Principle:
     • Steam Generation: Steam is produced within the chamber by a heating unit.
     • Air Removal: Steam displaces air through vents, ensuring that the chamber’s contents are effectively sterilized.
   • Types:
     • Horizontal Autoclave: Features a front-opening lid, suitable for larger volumes and high-throughput environments.
     • Vertical Autoclave: Opens from the top, typically used in smaller laboratories.
   • Applications: Ideal for sterilizing flat items like surgical tools, where air displacement is crucial.
3. Positive Pressure Displacement Autoclave (B-Type)
   • Description: Utilizes a separate steam generator to produce steam quickly, which is then directed into the autoclave.
   • Operational Principle:
     • Steam Generation: Fast steam production enhances the efficiency of the sterilization process.
     • Pressure Management: The steam is introduced under positive pressure, improving the overall speed of sterilization.
   • Applications: Suitable for scenarios requiring rapid steam generation and efficient sterilization cycles.
4. Negative Pressure Displacement Autoclave (S-Type)
   • Description: This advanced autoclave integrates both a steam generator and a vacuum generator.
   • Operational Principle:
     • Vacuum Generation: A vacuum generator removes air from the chamber before steam introduction.
     • Steam Penetration: With the air removed, steam penetrates more effectively, achieving high sterility assurance.
   • Advantages:
     • Accuracy: Provides precise control over sterilization conditions.
     • Sterility Assurance: High level of reliability in ensuring the removal of microorganisms.
   • Applications: Recommended for critical applications requiring the highest level of sterilization efficacy. However, it is also the most expensive type.
5. Pre-Vacuum Autoclave
   • Description: Utilizes a vacuum pump to evacuate air from the chamber before steam is introduced.
   • Operational Principle:
     • Vacuum Creation: The vacuum pump removes air, improving steam penetration and contact with materials.
     • Enhanced Sterilization: Effective for sterilizing heavy or complex loads.
   • Applications: Used in settings requiring thorough sterilization of intricate or dense items.

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.

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.

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.

How Does an Autoclave Work?

An autoclave, a device commonly employed in various fields, operates on principles akin to those of a pressure cooker. Its primary function is to achieve effective sterilization by subjecting materials within a sealed chamber to high-pressure steam at elevated temperatures. This process necessitates several distinct phases to ensure successful sterilization:

1. Purge Phase: At the commencement of the autoclave cycle, steam is introduced into the chamber. This steam displaces the air, gradually elevating the temperature and pressure within the chamber. The expulsion of air is imperative, as it can impede the sterilization process. The air removal can be facilitated through the use of a vacuum system or a sequence of steam flushes and pressure pulses. Gravity-type sterilizers utilize steam to force air downwards and out through the sterilizer drain.
2. Exposure (Sterilization) Phase: Subsequent to the purge phase, the autoclave’s control system closes the exhaust valve, initiating the exposure or sterilization phase. During this phase, the interior temperature and pressure rise to the predetermined setpoint. The temperature is diligently sustained at the desired level for the requisite duration, ensuring proper sterilization of the items within.
3. Exhaust Phase: Upon the completion of the sterilization phase, the autoclave enters the exhaust phase. In this phase, the pressure within the chamber is released through the exhaust valve. The interior returns to ambient pressure conditions while the contents of the chamber remain hot, ensuring that sterilized items maintain their sterile state.

The triumvirate of time, temperature, and steam quality is paramount to the efficacy of steam sterilization in autoclaves. Proper air removal from the chamber is pivotal since air impedes sterilization. This expulsion of air can be achieved using vacuum systems or steam displacement techniques. Gravity autoclaves utilize steam to displace air and direct it toward the sterilizer drain.

During the exposure phase, continuous admission of steam into the chamber is crucial to rapidly increase both pressure and temperature to the specified sterilization parameters. Maintaining the items within the autoclave at the designated sterilization temperature for the prescribed duration is essential to achieve reliable sterilization outcomes.

In the final phase, the exhaust phase, the sterilizer drain is opened to expel steam, allowing for depressurization of the chamber while ensuring that the sterilized items are adequately dried.

The quality of the steam utilized in the autoclave is a critical factor for effective sterilization. Ideally, the steam should consist of approximately 97% steam (vapor) and 3% moisture (liquid water). This composition optimizes heat transfer efficiency. Superheated steam, which contains less than 3% moisture, is not suitable for steam sterilization, as it lacks the requisite moisture content for effective heat transfer.

By meticulously adhering to these prescribed processes and rigorously maintaining the specified conditions of time, temperature, and steam quality, autoclaves are proficiently employed in healthcare settings to sterilize medical devices and various materials, ensuring the highest standards of hygiene and safety.

Precautions

When operating an autoclave, adhering to proper precautions is essential to ensure both the effectiveness of sterilization and the safety of the operator. The following precautions should be observed:

1. Avoid Sterilizing Inappropriate Materials
   • Waterproof or Water-Resistant Substances: Substances such as oils or powders should not be sterilized in an autoclave. These materials do not interact well with steam and may cause damage or ineffective sterilization.
   • Flammable, Reactive, Corrosive, Toxic, or Radioactive Materials: Materials that fall into these categories should never be placed in an autoclave. They can pose significant risks, including fire hazards or chemical reactions.
2. Ensure Proper Loading
   • Avoid Overcrowding: The autoclave chamber should not be overcrowded. Materials should be arranged to allow adequate steam circulation and penetration. Overloading can hinder the sterilization process and lead to ineffective results.
   • Spacing and Placement: Items should be placed so they do not touch the sides or top of the chamber. This spacing allows for even steam distribution and prevents blockages in steam flow.
3. Use Suitable Containers and Wrapping
   • Secondary Containers: Items to be autoclaved should always be placed in secondary containers to prevent contamination and ensure organized sterilization.
   • Autoclavable Bags: Only use bags specifically designed for autoclaving when packaging waste. These bags are made from materials that can withstand high temperatures and pressures.
   • Wrapping Materials: Articles should be wrapped in materials that permit steam penetration. Avoid using materials like aluminum foil, which can obstruct steam flow.
4. Manage Liquids Properly
   • Sealed Containers: Do not autoclave liquids in sealed containers, as the pressure build-up can cause the container to burst.
   • Fill Levels: Liquids should be filled to no more than two-thirds of the container’s total volume. This precaution helps to prevent spillage and potential damage.
5. Handle with Care
   • Avoid Opening During Operation: Never attempt to open the autoclave lid while the machine is in operation. Doing so can result in exposure to high-pressure steam and potential injury.
   • Plastic and Polyethylene Trays: Avoid using trays or containers made from plastic or polyethylene, as they may melt or deform under the high temperatures of the autoclave.
6. Special Waste Handling
   • Separate Waste: Autoclave biohazardous waste separately from clean items to avoid cross-contamination.
   • Paper Handling: Paper should not be placed directly inside the autoclave due to its combustibility. Instead, it should be autoclaved in a designated waste or biohazard bag to reduce fire risk.

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.

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.

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.

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.

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.

Quiz Practice on Autoclave

What is the primary purpose of an autoclave in healthcare and laboratory settings?

a. Sterilizing surgical instruments
b. Refrigerating samples
c. Heating food
d. Cleaning glassware

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Which component of an autoclave is responsible for indicating the pressure inside the chamber during sterilization?

a. Pressure Gauge
b. Water Level Indicator
c. Whistle
d. Control Panel

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What is the significance of a safety valve in an autoclave?

a. To control the temperature
b. To prevent contamination
c. To release excess pressure
d. To regulate the timer

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In an autoclave, which component is responsible for maintaining the appropriate water level?

a. Pressure Gauge
b. Water Level Indicator
c. Whistle
d. Safety Valve

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What is the primary function of a vacuum generator in certain autoclaves?

a. To generate steam
b. To extract air and create a vacuum
c. To cool the chamber
d. To regulate pressure

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Which component of an autoclave helps to prevent damage to drainage pipes by cooling the effluent?

a. Pressure Gauge
b. Vacuum Generator
c. Wastewater Cooler
d. Electrical Heater

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What is the primary role of the control panel in an autoclave?

a. To regulate pressure
b. To indicate the water level
c. To control electricity supply
d. To release excess pressure

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Which component is responsible for creating a hermetic seal on the autoclave to ensure proper sterilization?

a. Water Level Indicator
b. Safety Valve
c. Lid/Door
d. Pressure Gauge

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What is the primary function of the electrical heater in an autoclave?

a. To indicate temperature
b. To create a vacuum
c. To generate steam by heating water
d. To regulate pressure

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In some types of autoclaves, what does the whistle do after the sterilization process is complete?

a. Regulates pressure
b. Releases excess steam
c. Sounds an alarm
d. Signals that sterilization is finished

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FAQ on Autoclave

References

1. (ANSI) American National Standards Institute Inc./(AAMI) Association for the Advancement of Medical Instrumentation
2. https://www.britannica.com/technology/autoclave
3. https://university.steris.com/course/understanding-steam-sterilization/
4. https://www.cdc.gov/hicpac/Disinfection_Sterilization/13_0Sterilization.html
5. https://www.cdc.gov/infectioncontrol/guidelines/disinfection/sterilization/steam.html
6. https://blink.ucsd.edu/safety/research-lab/biosafety/autoclave/index.html
7. http://www.theratronics.ca/PDFs/Autoclave_Temperature_and_Time_Pressure_Chart.pdf
8. https://tuttnauer.com/blog/autoclave
9. https://en.wikipedia.org/wiki/Autoclave
10. https://consteril.com/how-does-a-laboratory-autoclave-work/
11. https://www.labkafe.com/blog/autoclave-definition-uses-working-principle-and-types-labkafe/
12. https://www.fcbios.com.my/blogs/news-insight/autoclave-machine-principle-how-to-use-and-maintenance
13. https://www.mlsu.ac.in/econtents/2214_Unit%201_Autoclave.pdf
14. https://www.mesaustralia.com.au/blogs/news/autoclaves-principles-uses-types-procedures