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

What is an autoclave?

An autoclave is a device which finds applications in numerous scientific and medical institutions. Its work principle lies in using the pressure of steam for the cleansing of equipment and materials. During the autoclaving process, the following kinds of germs are killed: bacteria, viruses, and spores.

The basic idea of autoclave sterilization is that it uses moist heat to reach a high temperature, usually around 121°C or 250°F, at a higher pressure. The steam, being pressurized, penetrates the materials and raises their temperature to levels that can kill most germs. Therefore, this method ensures that all dirt and germs are erased, much better than just washing with soap and water.

Autoclaves operate by sealing all contents within a chamber and then applying steam at pressures usually ranging between 15 and 30 pounds per square inch (psi). The combination of heat and pressure ensures that even the toughest spores are killed, making it a very popular method of sterilizing laboratory glassware, surgical tools, and other equipment that can handle heat.

Autoclaves are very important in labs that work with harmful germs. They provide a dependable way to kill all germs that regular methods can’t handle. The sterilization process usually has three parts: heating, keeping the temperature and pressure steady, and cooling down before the chamber is opened and air pressure is released.

The autoclave ensures that all equipment and materials in laboratories and healthcare facilities are free from any harmful microorganisms, thus keeping the environment in a sterile manner that is safe and accurate for 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?

• An autoclave works by using moist heat to ensure that sterilization is effective. This sterilizer uses high-pressure steam to boil water to extremely high temperatures above 100°C. That makes it a necessary tool, considering that in this autoclave, steam with a pressure of about 121°C, or 15 psi, acts upon the object for sterilization purposes.
• In a normal setting, water boils at 100°C. In an autoclave, though, when the pressure is increased, so does the boiling point of the water. Therefore, steam is able to be hotter, enabling heat to penetrate materials faster and deeper so that even hardy spores of microorganisms are destroyed. Once it cools and condenses to water again, on cooler surfaces, the water releases the extra heat and therefore kills all the microorganisms completely.
• Moist heat sterilization kills the microbes by causing their proteins to clump together. This process permanently damages the cells of the microorganisms, and hence they die. High-pressure steam fills the autoclave chamber, ensuring that all surfaces and materials are evenly exposed to the steam. This steam heats the materials and also goes deep inside, ensuring thorough sterilization.
• Once the sterilization process is over, the pressure in the chamber is released slowly. This is normally done using a pressure-regulating device that returns the pressure to normal levels. As the pressure drops, the steam changes back into water, and the temperature of the materials inside will start dropping as well. The material needs to be held at the sterilization temperature for a sufficient period of time, usually 15-20 minutes, so that the materials are fully sterilized, especially in larger quantities or in large items.
• An autoclave will only function correctly if it has reached a high temperature, along with steam reaching all parts and exerting pressure. All the microbial life is killed, even the spores.

Autoclave Parts/ Components

An autoclave is composed of a number of crucial parts, and each part has an important role in how it functions and the effectiveness of the outcome. Understanding what these parts are helps in utilizing and maintaining the device.

• Pressure Chamber
  • Inner Chamber: It is the compartment in which items to be sterilized are placed. It is made of stainless steel or gunmetal, especially constructed to face pressure and high temperature.
  • Outer Jacket: The outer jacket goes around the inner chamber. It is usually made of iron and filled with steam. This design helps heat things up faster and keep the right temperature for sterilization.
• Lid/Door
  • Sealing Mechanism: The lid makes sure there is an airtight seal to keep a controlled environment inside the autoclave. It is held in place with screw clamps and usually has an asbestos washer to ensure a tight fit.
  • Pressure Gauge: It is situated on the lid and monitors the internal pressure so that the autoclave functions safely and efficiently.
  • Pressure Releasing Unit/Whistle: This part controls the pressure by allowing steam to escape when the pressure becomes too high.
  • Safety Valve: It is a safety valve with a rubber layer that ruptures at very high pressure so that the system does not create accidents or explosion.
• Steam Generator/Electrical Heater
  • Steam Generation: This is the bottom part of the chamber. It heats water to produce steam. Water levels should be maintained to avoid overheating or inefficient steam generation.
  • Heating System: The electric heater ensures that the water reaches and maintains the temperature required for effective sterilization.
• Vacuum Generator (if applicable)
  • Air Removal: Some autoclaves have an air evacuator to remove air from the chamber. This is essential to remove air pockets that could harbor microorganisms, allowing steam to penetrate completely.
• Wastewater Cooler
  • Cooling System : It is important because it cools the effluent before it leaves the autoclave to prevent scalding of drainage pipes. The cooling system also helps extend the life of the autoclave as well as the attached piping.
• Other parts
  • Control Panel: This is a panel located beside the main switch, which controls the temperature and pressure settings in the autoclave.
  • Water Level Indicator: This is used to show the water level in the chamber so that the correct amount is maintained for efficient operation.
  • Thermometer: It shows the internal temperature, giving essential feedback so that sterilization conditions are met.
• Accessories
  • Autoclave Bags: These bags are used for placing waste materials to be sterilized. They ensure proper containment during the process.
  • Autoclave Baskets: These baskets move materials into and out of the autoclave safely. They have different sizes and shapes for various items. Sterilization Boxes: This is a stainless steel box with a lid and a vent designed 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 works to sterilize the material rapidly with proper, step-by-step procedures. The general procedure on running an autoclave is illustrated in detail below, emphasizing the primary components of the procedure:

• Pre-run preparation
  • Verify the autoclave: If there are materials carried over from run to run, make sure that the chamber does not have residual material.
  • Water Addition: Sufficient water must be added to the chamber. This water is used in order to generate steam, which is the principal agent of sterilization.
• Loading Materials
  • Positioning: Materials that have to be sterilized must be loaded into the chamber. Articles must be arranged in such a way that steam can penetrate effectively. In certain materials, such as glassware, it is essential to wrap in sterilization paper.
• Sealing and Heating
  • Lid Closure: The lid of the autoclave is closed and screw clamps are tightened for a tight seal. This way, steam cannot escape during the cycle.
  • Heating: The electric heater is turned on, and heating starts. Steam is produced as a result, which is necessary for reaching the temperature required for sterilization.
• Pressure and Steam Management
  • Safety Valve Adjustment: The safety valve must be adjusted so that the pressure in the chamber remains at the appropriate level. The standard pressure is usually 15 psi, equivalent to a temperature of 121°C.
  • Air Displacement: Let the steam and air mixture out through the discharge pipe when the water boils. This step is very important to get rid of air from the chamber because leftover air can stop proper sterilization. Make sure all the air is gone when no more air bubbles show up in the discharge stream.
• Sterilization Phase
  • Pressure Setting: Close the discharge pipe once all the air has been forced out. Allow the steam pressure to build up to the level set. The autoclave will maintain this pressure to aid in sterilization.
  • Sterilization Time: The sterilization cycle typically takes 15 minutes. In this period, the high temperature and pressure will kill the germs in the materials.
• Cooling and Pressure Release
  • Heater Shutoff: After the holding period, switch off the electric heater. Let the autoclave cool down on its own. Check the pressure gauge to ensure that the pressure inside the autoclave has dropped to atmospheric pressure before proceeding.
  • Air Intake: Slowly open the discharge pipe to allow air into the chamber. This allows the pressure inside the autoclave to return to normal to safely open it.
• Completion
  • Lid Opening: Once the pressure is balanced and chamber has cooled to that extent, open the lid.
  • Material Removal: Remove the now sterilized materials from the chamber with utmost care. Sterile equipment or gloves must be used in order to preserve the sterility of these materials.

Air removal form Autoclave

It is very essential to remove air from the autoclave for proper sterilization. Air trapped inside may make it difficult to attain sterility because air is not as effective in sterilization as steam. There are several methods for removing air in autoclaves:

1. Downward Displacement (Gravity-Type): In this technique, steam enters the chamber and fills the top regions first, displacing the lighter air downwards. The compressed air is drained out through a drain, which is usually equipped with a temperature sensor. It stops flowing when the space is drained. Control will normally be by means of a steam trap, solenoid valve, or bleed holes. It can also force out the steam-air mixture from the rest of the enclosure, not just the bottom.
2. Steam Pulsing: Air dilution is obtained 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 utilize both vacuum and steam pulses produced by a vacuum pump. The cycle starts with a vacuum, then has a steam pulse, followed by another vacuum, and continues this way. The number of pulses is dependent on the type of autoclave and sterilization cycle chosen. Superatmospheric cycles are very similar to subatmospheric cycles, but they use vacuum and steam pulses. The pressure in the chamber never exceeds atmospheric pressure until it reaches the sterilizing temperature.

Notable to this is the fact that automatic air removal programs may be missing in some of the stovetop autoclaves found in non-medical or less privileged settings. Here, the operator has to perform steam pulsing at specific pressures indicated by the gauge to aid in air removal.

Proper air removal from the autoclave ensures effective sterilization; hence, safe and reliable equipment, instruments, or other items are provided for use.

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

Autoclaves are useful machines for cleaning many materials. However, it is essential to know the materials that could be safely put in an autoclave and those that shouldn’t. Here are some examples of materials that may go into an autoclave and those that cannot go in one:

Autoclave Compatible Materials:

• Glass: Only Pyrex ^{®} glass or Type I borosilicate glass can endure autoclaving. If you are using Pyrex ^{®} containers, do not fill them more than two thirds full, and do not close them.
• Polypropylene: Polypropylene is a relatively inexpensive resin which can tolerate autoclave sterilizing temperatures. Polypropylene containers are often viewed as secondary containers for products autoclaved.
• Stainless Steel: Almost all metals are acceptable in the autoclave, including stainless steel. Remove plastics, liners, and any other material that will melt or catch fire in the autoclave before loading the autoclave.
• Pipette Tips: Most plastic pipette tips, even those made from high-density polyethylene, may be loaded into the autoclave. Generally, pipette tips are placed inside a biohazard bag as waste and autoclaved on steam mode.
• Media Solutions: Do not autoclave liquids in sealed containers. Fill containers to two-thirds full and take off the tops. Autoclave media solutions using a cycle that makes steam.
• Tissue Culture Flasks, Litter, and Pet Food: These items usually work with autoclaves and can be sterilized well.

Autoclave Incompatible Materials

• Chlorine, Hypochlorite, Bleach: These chemicals cannot be autoclaved and should not be put in an autoclave.
• Acids, Bases, and Organic Solvents: It may be dangerous to autoclave these. Do not autoclave them.
• Chlorides, Sulphates, Sea Water: These are poor autoclaving materials and tend to harm the autoclave.
• Polystyrene, Polyethylene, Polyurethane: Do not autoclave lab equipment manufactured from these. They may melt or distort.

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

Three main classes of autoclaves exist, each providing different features and capabilities.

1. Class B Autoclaves: Class B autoclaves are actually the most sophisticated steam sterilizers. In a Class B autoclave, there is an independent steam generator that rapidly generates steam, which is then forced into the autoclave chamber. The main feature of a Class B autoclave is the post-sterilization vacuum drying process. This implies that all products sterilized are dry when the cycle of sterilization is finished. Class B autoclaves are used in different institutions, including hospitals, dental offices, labs, and tattoo studios. These follow the standard certification requirements, such as NF EN13060, and ensure the health and safety rules in place 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 usually quite simple and only offer basic features of sterilization.
3. Class S Autoclaves: Class S autoclaves are in the middle between Class N and Class B. These autoclaves can sterilize tools that are single-wrapped, multi-layered, and larger than what Class N autoclaves can sterilize. Class S autoclaves are fitted with a vacuum pump to help remove air from the chamber before starting the sterilization process. They are not able to remove the air as completely as Class B autoclaves. Class S autoclaves are more versatile than Class N ones, so they might meet more diverse types of the needs for the sterilization procedures.

The choice of autoclave should depend on the needs of the material and instruments that are to be sterilized. The nature of the items, the degree of air removal needed, and drying capabilities will be the basis of the class of autoclave to be chosen for effective sterilization.

What Is The Autoclave Cycle Time Frame?

• There are phases in the autoclave cycle time, and one of them is the exposure time, which simply means how long it takes to sterilize the device. But, exposure time is only one aspect of the overall cycle time.
• The time for steam sterilization is determined by scientific tests. It takes into account various factors such as the size, shape, weight, density, and materials of the device to be sterilized. These factors influence how long it will take to ensure that sterilization works well.
• Proper sterilization requires observing the recommended duration of the steam. In this respect, the precise time will be subject to change due to variations in methods used as well as types of things cleaned.
• The duration of an autoclave cycle is based on the amount of time that should be taken to ensure good exposure to the things in it. This includes preparation time before the cycle, removing air, adding pressure, and drying afterward. All these parts together form the total time needed for effective sterilization in an autoclave.

Factors Affecting Sterilization Effectiveness

Many factors can influence how effective autoclave sterilization will be. Some of these should be considered for the best outcome in sterilization. Some key points are highlighted below:

• Cleaning: In case instruments are not cleaned appropriately before sterilization, more germs, proteins, and salt will be available. Such impurities will dilute the effect of sterilization. Organic and inorganic residues must be completely removed by thorough cleaning of instruments.
• Salt: Any salt that dries on the equipment or material can interfere with the sterilizing process and therefore undermine its effectiveness. Items should, therefore, be cleaned properly with no salt accumulation.
• Restricted Flow: The sterilant, usually steam, needs to touch microorganisms to work well for sterilization. Objects that have complex shapes or sharp turns can stop the steam from moving properly, which may mean the sterilant can’t reach all parts, making sterilization less effective.
• Protein: Leftover proteins on tools or materials can make sterilization harder. It is important to follow proper cleaning steps to remove protein leftovers completely.
• Microbial Load: The amount of pathogens on instruments or materials before sterilization may impact effectiveness. Higher pathogen loads often require longer exposures or additional decontamination methods to ensure comprehensive sterilization.
• Cluttered Autoclave: Avoid overpacking the autoclave chamber with too many products. Sufficient space should remain in the autoclave to allow steam access around the packed items. Autoclave chocking may increase the chances for inadequate steam access and inconsistent exposure to sterilant.
• Positioning: Autoclave clean items and waste items separately. This would prevent cross-contamination and ensure that both get sterilized well. There should not be contact between the items inside the autoclave chamber and the sides or top. The space must allow steam to distribute evenly around the items.
• Choosing the Right Cycle: It is very important to pick the right sterilization cycle for good sterilization. Wrong cycles may lead to poor sterilization, damage to an autoclave, a spill of liquid, broken bottles or containers, and more.

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

• The autoclave works by subjecting the materials or objects to moist heat at high temperatures as a device that utilizes heat for sterilization. Destruction of bacteria and other microorganisms occurs through the application of heat upon utilizing an autoclave.
• Moist heat is very effective in killing microorganisms because it can denature and coagulate the proteins and enzymes that are present in the bacterial cells. In the autoclave, high temperatures penetrate the cells, causing irreversible changes in the structure of the proteins and enzymes.
• Denatured and coagulated proteins disturb the important functions of bacterial cells. They cannot survive, multiply, or produce diseases. An autoclave has a very high temperature; usually, the temperature ranges between 121°C to 250°F or more for the effective killing of microorganisms.
• Humidity in the autoclave also contributes to enhancing the sterilization procedure. Wet heat is preferable over dry heat because wet heat penetrates into microorganisms and breaks down proteins. The heat and water mixture of the autoclave creates an environment that kills bacteria, viruses, fungi, and all types of other microorganisms.
• The autoclave uses the right temperature and pressure for long enough to ensure that all microorganisms on the surfaces or inside the objects are fully killed. This makes the autoclave a reliable means of achieving sterilization and thus prevents infections from spreading.
• The autoclave works mainly by heat, and it is not right for every kind of material. Some items or substances that are sensitive to heat may need different ways to be sterilized to keep them safe and effective.
• The autoclave works by employing moist heat to destroy microorganisms. This makes proteins and enzymes change shape and ultimately break down. In this sense, the small organisms cannot exist or multiply because of the denatured condition.

How Does an Autoclave Work?

An autoclave is one device that has frequently been applied in various areas. It acts just like a pressure cooker. It mainly functions by sterilizing substances using high-temperature, high-pressure steam within an enclosed environment. The autoclave process contains the following stages to ensure sterilization is properly performed:

1. Purge Phase: The first step in the autoclave cycle involves the entrance of steam into the chamber. This steam displaces the air in the container; it slowly increases the temperature and pressure in the sterilizer. Air must be completely removed because it would interfere with the process of sterilization. The air may be evacuated by either vacuum system or series of steam flushes and pressure pulses. Gravity-type sterilizers function by using steam to force the air downwards and out through the sterilizer drain.
2. Exposure (Sterilization) Phase: The control system of the autoclave closes the exhaust valve after the purge phase. The temperature and pressure inside will rise to the set point during the exposure or sterilization phase. The temperature is kept at the right level for the duration required to make sure the items are properly sterilized.
3. Exhaust Phase: After the autoclave completes its sterilization cycle, it enters an exhaust phase. In this phase, the pressure inside the chamber is passed off through the exhaust valve. The inside of the chamber returns to ambient pressure conditions, while the contents of the chamber remain hot so that the sterility of sterilized items is maintained.

The critical nature of time, temperature, and quality of steam makes the operation of autoclaves effective in steam sterilization. There is a need to remove air from the autoclave chamber because it slows down the sterilization process. This is possible by either vacuuming systems or by the ways of steam displacement. Gravity autoclaves depend on the action of steam that pushes air out and drains into the sterilizer.

It is very fundamental to use great quantities of steam during the exposure phase to raise the pressure and temperatures rapidly enough for the needed sterilization levels to be reached. The holding time at the required sterilizing temperature is crucial in ensuring that the items inside the autoclave are fully sterilized.

In the last phase, called the exhaust phase, the sterilizer drain is opened to release steam. This helps lower the pressure in the chamber and makes sure that the sterilized items are dried well.

The proper quality of steam in the autoclave is very important for proper sterilization. Ideally, the steam should be about 97 percent steam, vapor, and 3 percent moisture, liquid water. This mix helps heat transfer work better. Superheated steam containing less than 3 percent moisture is not good for steam sterilization because it does not have enough moisture to allow effective heat transfer.

With proper observance of these set steps and strict maintenance of the right steam time, temperature, and steam quality, autoclaves are applied in health facilities as an efficient sterilizer for medical appliances and various items that meet the conditions for hygiene and safety.

Precautions

When using an autoclave, it is important to follow safety rules to make sure it works well and keeps the user safe. Here are some safety rules to follow:

• Do Not Sterilize Wrong Materials
  • Waterproof or Water-Resistant Things: Do not put oils or powders in an autoclave. These things do not work well with steam and can cause problems or not sterilize properly.
  • Flammable, Reactive, Corrosive, Toxic, or Radioactive Materials: These types of materials should never be loaded into an autoclave. They can present serious hazards such as fire and chemical reactions.
• Load Correctly
  • Do not Overcrowd: The autoclave chamber must not be overloaded. Materials must be placed to allow for good steam circulation and penetration. Overloading can hinder the sterilization process and yield ineffective results.
  • Spacing and Positioning: Items should be placed in a way that they are not touching the sides or the top of the chamber. The spacing allows steam to spread out evenly and prevents blockages in the steam flow.
• Use Appropriate Containers and Wrapping
  • Secondary Containers: Items that are to be autoclaved should always go into secondary containers to avoid contamination and make sterilization organized.
  • Autoclavable Bags: The waste packaging bags should be autoclavable, which allows the bags to endure high temperature and pressure.
  • Wrapping Materials: Wrap materials in a way that allows steam penetration. Materials like aluminum foil cannot be used as they will block steam penetration.
• Manage Liquids Properly
  • Sealed Containers: Liquid waste should not be autoclaved in sealed containers as the bursting pressure can damage the container.
  • Fill Volumes: The liquid should fill a container up to two-thirds of the full volume. It helps prevent spilling and thus potential damage.
• Handle Carefully
  • Never Open During Cycle: The lid should never be opened while the autoclave is running. In case it does, there would be exposure to high-pressure steam, which would be dangerous for humans.
  • Plastic and Polyethylene Trays: Do not use plastic or polyethylene trays or containers since they melt or deform with very high temperatures that are associated with the autoclave process.
• Special Waste Management
  • Separation of Waste: Sterilize the biohazardous waste apart from the other clean materials in order to prevent cross-contamination.
  • Paper should not be put directly into the autoclave because it is prone to burning. It should be put in special waste or biohazard bag before autoclaving to lower the risk of fire.

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

• There is a biological indicator, which is also called a biological spore test or spore strip, that checks how well sterilization processes work, especially in autoclaves. Very strong bacterial spores are used to check if the autoclave did a good job of killing the germs.
• Geobacillus stearothermophilus (formerly known as Bacillus stearothermophilus) spores are one of the most common life signs used in science. These spores are highly resistant to steam and serve as a reliable sign of autoclave function. They can handle high temps and need a certain amount of time and temperature to be completely destroyed.
• The Centers for Disease Control and Prevention (CDC) suggest testing the autoclave once a week with a culture containing heat-resistant endospores of Geobacillus stearothermophilus to see how well it works. A soft plastic vial with a growth medium and spores ampule is what most commercially available spore strips are made of.
• During the test, the spore strip is put in the middle of the load, which is the stuff that needs to be cleaned, in the sterilizer. The autoclave cycle is then started, exposing the spores to the stated time and temperature conditions. The inner ampule of the bottle is broken after the cycle, letting the growing medium out.
• After that, the whole container is put in an incubator with the right temperature and humidity. This includes the spore strip and medium. If there is no growth in the culture after incubation, it means that the sterilizer did a good job of sterilizing the load, and the process is considered successful. The fact that bacteria didn’t grow in the autoclave shows that the temperature and length of time used were just right to kill the very tough Geobacillus stearothermophilus spores.
• Biological indicators are a useful way to check the quality of sterilizer cleaning and make sure it works every time. They give a more accurate evaluation than just using physical signs like temperature and pressure gauges because they directly measure the death of microorganisms.
• Healthcare facilities, labs, and other places can make sure their autoclave processes work by regularly testing biological indicators. This way, they can keep up a high level of cleaning to stop the spread of dangerous 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 used to visually evaluate autoclave sterilization. These tapes have a heat-sensitive chemical indicator that changes color or marks when sterilized at 121°C.
• Autoclave tapes quickly verify that the package or load was sterilized at the right temperature. Diagonal stripes, “sterile,” or “autoclaved” on the tape indicate sterilization at the effective temperature.
• To ensure heat penetration and sterilization, tapes are put within the autoclave and toward the center of big packages or loads. To sterilize the entire load, heat penetration is essential, like cooking the middle of a huge piece of meat. Place the tapes in these spots to infer that heat penetration has occurred if the tape changes color or has marks.
• Remember that autoclave cassettes have limits. They don’t say how long sterilization was proper. They only show when the temperature threshold is achieved. The tape does not show pressure, duration, or steam quality, which are essential for sterilization.
• Autoclave tapes can provide a quick visual cue, but they should not be used to verify sterilization. To guarantee autoclave efficacy and material or instrument sterilization, biological markers should be utilized.
• Autoclave tapes with heat-sensitive, chemical indications are adhesive-backed paper tapes that visually certify sterilization temperature. A heat penetration indicator is positioned within or near the middle of packages or loads. They do not give time or other key sterilization characteristics, making them an additional tool rather than a complete validation technique for autoclave sterilization.

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

• Other sterilization indicators include thermocouples and Browne’s tubes, as well as autoclave tapes.
• One end of a thermocouple connects two metal wires to measure temperature. When heated, the wire junction generates a voltage proportional to temperature. This voltage is then measured by a potentiometer or temperature measuring equipment, producing an exact temperature measurement. Medical, scientific, and manufacturing industries utilize thermocouples to record sterilization temperature profiles. Their real-time temperature data helps regulate the sterilizing temperature.
• Albert Browne devised Browne’s tube in 1930 as a sterilization indicator. The glass tube contains heat-sensitive red dye. After a certain time at a certain temperature, the dye turns red to green. Dye color conversion indicates time and temperature. Browne’s tubes show if the target temperature and exposure duration have been met, determining sterilizing effectiveness. They show sterilization conditions.
• Thermocouples and Browne’s tubes provide more information than autoclave cassettes. Temperature observations via thermocouples provide sterilization monitoring and control. Browne’s tubes, on the other hand, give a visible representation of both temperature and time, giving insight into the length of exposure at a certain temperature.
• These indicators help validate and manage sterilization operations. They guarantee sterilization efficiency by ensuring temperature and exposure duration are fulfilled. Thermocouples, Browne’s tubes, autoclave tapes, and other monitoring systems can provide additional data and improve sterilization dependability.

What is Autoclave Cycle?

Autoclave cycles are the exact settings and conditions that are used to sterilize something in an autoclave. The cycle that is used depends on the load that is being cleaned and how it is made. These are some common cycles for an autoclave:

• Cycle for Liquids: This cycle can be used to sterilize liquids. It needs to be put in glass cases with lids that have vents and are only two-thirds full. Different types of liquids can be sterilized, such as liquid media, non-flammable liquids, liquid biological garbage, aqueous solutions, and others. A slower exhaust is usually part of the cycle to keep the liquids from getting too hot and boiling over.
• Solids or Dry Cycle: This cycle is made to sterilize things that are solid or dry. It can be used for dry goods that aren’t wrapped or are stored in porous materials, metals, non-porous materials, and things like empty wine glasses. Because it won’t boil over like in the liquids cycle, a fast exhaust cycle can be used for this one.
• Wrapped Goods or Pre-Vacuum Cycle: This cycle is used to sterilize wrapped items or things that need to be in a pre-vacuum state. People often use it to package things, like pipette tips and biohazardous waste in sterilizer bags. This cycle can also be used for sterilizing kitchenware that needs to be dried upright. Before adding steam, the pre-vacuum cycle helps get rid of any air in the room. This makes sure that the wrapped items are properly sterilized.
• Sharps Disinfection: This cycle is meant to clean and sanitize sharp objects like scalpels and needles. It makes sure that these things are completely germ-free, which lowers the chance of spreading illness.

It is important to keep in mind that the settings and lengths of these autoclave processes may be different based on the autoclave model and maker. To sterilize something properly, the temperature should be 121°C, and the cycle should keep it that way for at least 30 minutes with full steam at a pressure of at least 15 psi. However, longer cycle times may be needed to make sure proper cleaning, based on the make-up and size of the load. It is important to follow the autoclave manufacturer’s directions and instructions for choosing the right cycle and using the machine correctly in order to get good sterilization results.

Safety Tips to Observe When Using the Autoclave Sterilizer

Safety is paramount while using an autoclave sterilizer. Some important safety tips:

• Training: Ensure that laboratory workers are appropriately educated before utilizing a certain model of autoclave. Learn the operational and safety procedures.
• Avoid Overcrowding: Do not overcrowd the autoclave chamber. Allow space between things for optimal sterilizing.
• Secondary Chamber: Put autoclaved things in a secondary container. This prevents contamination and improves sterilizing.
• Bags autoclavable: Only use autoclavable bags for packaging and autoclaving materials or waste. Sterilization-resistant bags.
• Wrap the materials to allow steam penetration. Aluminum foil may impede steam circulation.
• Chamber Contact: Keep things inside the chamber from touching the sides or top. Proper spacing sterilizes evenly.
• Lid Safety: Never attempt to open the autoclave’s lid while it is operating. Let the pressure dissipate before examining the contents.
• Avoid cross-contamination by autoclaving clean and waste items separately.
• To avoid spillage during sterilization, fill liquid-containing vessels no more than two-thirds full.
• Avoid autoclaving liquids in sealed containers. Pressure can cause explosions. Vent properly.
• Pre-Heating Check: Before pre-heating the autoclave, check for any prior things left inside to prevent any dangers.
• Water Level: Check the autoclave water level before sterilizing. Deficient water might ruin the machine.
• Secure Lids: Close the autoclave lids snugly and ensure the screws are secured properly before powering on the electric heating.
• Post-Sterilization Cooling: Do not open the autoclave or touch the materials after sterilization. Let them cool first.
• Avoid Sealing Autoclavables: Autoclaved items should not be sealed to avoid explosions.
• Positioning: Never stand directly in front of the autoclave door. Avoid close contact when operating.
• Maintenance and Reporting: Maintain the autoclave and examine its operation. Report valve leaks, temperature changes, and gasket degradation to the relevant authority.

Uses of Autoclave

Autoclaves are flexible and used in many ways. Common autoclave uses:

• Medical facilities use autoclaves to sterilize surgical tools, syringes, and other reusable equipment. Dressings, bandages, and linens are sterilized with them.
• Dental offices need autoclaves to sanitize drills, forceps, and probes. This keeps dental operations clean and safe.
• Laboratory: Research, microbiology, and biotechnology labs use autoclaves to sterilize glassware, pipettes, media, Petri dishes, and other equipment. It helps avoid contamination and protect the integrity of experiments and cultures.
• Pharma: Autoclaves sterilize equipment, vials, containers, and packaging. This assures drug safety and sterility.
• Veterinary clinics: Autoclaves are used in veterinary clinics and animal research facilities for sterilizing surgical instruments, lab equipment, and animal care supplies. This prevents infections and protects animals.
• Food processing facilities: Autoclaves disinfect food processing containers, packaging, and equipment. This improves food safety and shelf life.
• Prior to disposal, autoclaves sanitize biomedical waste such gloves, gowns, and other biomedical waste. This guarantees safe infectious material handling and disposal.

Advantages of Autoclave

• High efficiency: Autoclaves are known for their ability to sterilize things very quickly. Small living things like bacteria, fungus, and spores are killed by the high heat and pressure that steam creates.
• Versatility: Autoclaves can sterilize a wide range of materials, making them suitable for various applications. Autoclaves are a good way to clean metal, glass, plastic, and other heat-resistant materials.
• Autoclaves are made to be easy to use. They have control screens that let people set the temperature, pressure, and cleaning time they want. Once the settings are set, the autoclave works on its own and doesn’t need much help from you.
• Safety: Autoclaves are safe to use as long as you do it the right way and follow the manufacturer’s directions. They have safety features that keep accidents from happening and protect the person using them during the cleaning process.
• Value for money: Autoclaves save you money over time. They get rid of the need for extra chemicals or disposable items, which lowers the long-term costs of sterilization. Autoclaves are a reliable and inexpensive way to sterilize a wide range of materials once they are bought.
• Effective use of time: Using an autoclave takes less time than other ways of cleaning, like dry heat. When you combine high temperature and pressure, sterilization happens quickly and effectively, which saves time in busy labs or hospitals.
• Effective penetration: The steam that is made in autoclaves does a great job of getting into all areas of the things that are being cleaned. In this way, even in complicated or hard-to-reach places, the area is completely sterilized.
• Large capacity: Autoclaves come in different sizes, including larger types capable of sterilizing a significant amount of materials in a single run. Because of this, they can be used to sterilize a lot of items at once in places like hospitals, research labs, and factories.

Disadvantages of Autoclave

• wetness retention: Autoclaves sterilize things with steam, which can cause the cleaned items to hold on to wetness. This can be a problem for some things, like technology that are easily damaged or materials that are easily damaged by heat.
• Compatibility limitations: Autoclaves are ideal for sterilizing materials made of stainless steel and heat-resistant plastics. But they might not work for substances that are easily damaged by heat and can’t handle the high temperatures and pressure of the autoclave process. Additionally, certain materials such as powders and oils may not be effectively cleaned using an autoclave.
• Cost: Buying and maintaining an autoclave can be pricey, especially if it is a bigger or more modern type. The initial investment and continued costs connected with upkeep, calibration, and frequent servicing should be considered.
• Dimensions and weight: Autoclaves are usually big and heavy pieces of equipment, which can make them hard to store and move. Because they are big and heavy, autoclaves can’t be used in all places or need special facilities and room.
• Risk of harm: If an autoclave is used incorrectly, it can hurt the people who are using it. The high temperatures, pressure, and steam involved in the sterilization process can cause burns or cuts if safety precautions are not followed strictly.
• Limited compatibility with materials: Autoclaves might not be able to sterilize some things, like sharp objects or things that can catch fire. During the autoclave cycle, sharp tools can lose their edge or get broken, and materials that can catch fire can be a danger.

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