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Autoclave Definition, Working Principle, Components, Operating procedure.

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Autoclave definition – What is an autoclave?

An autoclave is a large vessel containing steam under high pressure. It mainly used to sterilize different materials in the laboratory. Autoclave heating up the material at a specific temperature for a specific period of time. It is also termed as steam sterilizers or steam autoclave.

Hence autoclave is based on the moist heat sterilization method, it considered the most reliable and effective method of sterilization among all physical methods.

The autoclave machine was invented by Charles Chamberland in 1879. Chamberland was a French scientist who developed the autoclave as a way to sterilize laboratory equipment using steam under pressure. His invention was based on the work of Louis Pasteur, who had demonstrated that heat could be used to kill microorganisms.


Chamberland’s original autoclave consisted of a glass tube sealed at one end and fitted with a valve. Steam was introduced into the tube, and the pressure was increased by turning a screw at the sealed end of the tube. Chamberland used his autoclave to sterilize a variety of materials, including laboratory equipment and biological specimens.

Since its invention, the autoclave machine has become an essential tool in laboratories and medical settings for sterilizing materials and equipment. It has undergone numerous improvements and modifications over the years, but the basic principles of operation have remained largely unchanged.

Autoclave Temperature

Differen tempareture rang are used for steam sterilization such as 250° F (121° C), 270°F (132°C) or 275°F (135° C). But, 121°C (250°F) and 132°C (270°F) are the two most common steam-sterilizing temperatures uses to kill microorganisms.

Autoclave Working Principle

Video demonstrating how autoclaves work

An autoclave works on a basic principle. The material is directly exposed to steam at the required temperature and pressure for a specific time. The boiling point of water will increase with the rising pressure as a result high temperatures will be generated for sterilization.

High-pressure helps in the rapid penetration of heat within the material and the pressure help in the coagulation of proteins.

Within the autoclave, the water boils at 121°C at the pressure of 15 psi or 775 mm of Hg. When the microbes come in contact with the steam it kills them by giving off latent heat. The specified temperature ensures the microbicidal activity.

When the autoclave door is closed and the chamber is sealed, a vacuum pump eliminates all air and replaces it with steam. Now, pressure is added to steam in order to obtain the appropriate sterilising time. Once the cycle is complete, the steam is exhausted and the laboratory equipment is removed with care.

For a more thorough explanation of the many phases of a sterilisation cycle, please refer to the following list and illustration.

How Does an Autoclave Work?
How Does an Autoclave Work? | Image Source: www.microlit.us
  • Purge Phase: Air must be evacuated from the chamber during the initial part of the sterilisation cycle, known as the Purge Phase. The vacuum system in the autoclave is designed to replace the air in the enclosed chamber with steam.
  • Exposure (Sterilization) Phase: Following the removal of air, the steriliser drain is sealed and steam is constantly introduced into the chamber, resulting in the necessary increase in chamber pressure and temperature. Now that the cycle has entered the exposure phase, the lab equipment is held at the sterilising temperature for the allotted duration.
  • Exhaust Phase: In the final phase, pressure is removed from the chamber through an exhaust valve and the internal pressure is returned to ambient.
Autoclave principle
Autoclave principle | Image Source: http://www.oorja.in/solar-heating/solar-autoclaving-sterlization/

Primarily, autoclaves use gravity, vacuum-induced, or pre-vacuum (pre-vac) sterilising techniques. Although some types of autoclaves combine both sterilisation methods:

Steam is pumped into the autoclave chamber during gravity autoclaving, also known as gravity displacement autoclaving. This drives ambient air out of the exhaust valves, allowing the remaining steam to sanitise the contents.

Gravity autoclaves are useful for sterilising non-porous materials, including the majority of metals, particularly stainless steel surgical tools and laboratory utensils, Pyrex® or borosilicate Type I glassware, biohazardous waste, and unpackaged commodities.

Gravity autoclaving
Gravity autoclaving

Autoclaving under vacuum is also known as autoclaving and pre-vacuum sterilisation. The vacuum function of these autoclaves permits deeper sterilisation of contents when air cannot be easily removed from the sterilisation medium, as it completely evacuates ambient air inside, allowing high-temperature steam to permeate and sterilise areas that would normally be occupied by ambient air.

Vacuum autoclaving
Vacuum autoclaving

Autoclaves are ideal for sterilising objects with porous or difficult-to-reach locations (wrapped surgical kits).

Factors Affecting Sterilization Effectiveness

CleaningInadequate instrument cleaning results in an increase in bioburden, protein burden, and salt concentration. These will diminish the efficacy of sterilisation.
SaltSalt residue reduces the efficacy of sterilisation.
Restricted FlowMicroorganisms must come into touch with the sterilant. Device designs (to-be-sterilized objects) that restrict or inhibit this contact (e.g., abrupt bends) will limit sterilization’s efficacy.
ProteinProtein residues reduce the efficiency of sterilising. However, cleaning appears to eliminate the protein swiftly.
Microbial load
Cluttered autoclaveThe autoclave must be clear of debris. Allow sufficient area for steam circulation.
Difference in cleanlinessGarbage and clean things must be autoclaved independently.
PositionObjects put within the chamber should not contact its sides or ceiling.
Choose the appropriate cycle typeIncorrect cycle selection can cause autoclave damage, liquid spillage, and bottle breakage.

Mode of Action

Moist heat destroys cells and viruses by degrading nucleic acids and denaturing enzymes and other essential proteins. It also disrupts cell membranes. Exposure to boiling water for 10 minutes is sufficient to destroy vegetative cells and eukaryotic spores. 

To destroy bacterial endospores, moist heat sterilization must be carried out at temperatures above 100°C, and this requires the use of saturated steam under pressure.

Components of Autoclave

A simple autoclave contain these following components such as;

1. Pressure Chamber/Vessel

  • The vessel is the autoclave’s primary body and is composed of an interior chamber and an exterior jacket. Laboratory and hospital autoclaves are constructed with “jacketed” chambers, which are filled with steam to expedite sterilisation cycles and reduce condensation.
  • A vessel designed and manufactured with a full jacket is superior to one with a partial or blanketed jacket for the following reasons: a full jacket improves temperature uniformity within the chamber, reduces the likelihood of wet packs, and aids in minimising wet steam, which is detrimental to sterilisation.
  • Every autoclave vessel in the United States is inspected and tagged with an American Society of Mechanical Engineers (ASME) nameplate bearing a National Board number.
  • Before using an autoclave, manufacturers are required to hydrostatically test each vessel and affix an ASME nameplate. This examination and the ASME nameplate are essential markers of an autoclave’s proper operation.
  • Autoclave vessels in laboratories and hospitals can range in size from 100L to 3,000L and are commonly made of 316L stainless steel. The inner chambers are either 316L or nickel-clad, and the exterior jackets are 316L, 304L, or carbon steel.

2. Lid/ Door

The lid is fastened by screw clamps and rendered airtight by an asbestos washer.  It contains different components such as;

  • Pressure releasing unit/ Whistle: Unlike a pressure cooker an autoclave contains a Pressure releasing unit or a Whistle. It maintain the pressure within the autoclave by releasing a certain amount of vapor.
  • Safety valve: All autoclaves run under heightened pressure (14–45 pound-force-per-square-inch gauge), necessitating a very sturdy design and a variety of safety measures and mechanisms to ensure that they pose no risk to users. One of these safety mechanisms is the safety valve, which serves as the pressure vessel’s final fail-safe device should all electronic controls fail. Based on the recommendations of the steriliser and/or valve manufacturer, as well as local inspection and insurance authorities, it is essential that the safety valve be inspected, tested, and verified to be in proper functioning order.
  • Pressure gauge: It is an essential component for the safety of the autoclave. During sterilization, it indicates the pressure created by the autoclave.

3. Steam generator/ Electrical heater

  • The main function of a Steam generator or Electrical heater is to produce steam from water.
  • It is located underneath the chamber.
  • It is important to keep the Electrical heater under the water. The coil of the Electrical heater will burn If the water level within the inner chamber is not sufficient.
  • The steam generator or electrical heater in an autoclave is a device that is responsible for producing the steam or heat that is used to sterilize the materials in the autoclave.
  • Sometimes, the steam generator or electrical heater is typically located outside the autoclave chamber and is connected to the chamber through a series of pipes or wires.
  • In a steam autoclave, the steam generator boils water to produce steam, which is then introduced into the autoclave chamber. The steam is used to heat the materials and create a high-pressure, high-temperature environment that is effective at killing microorganisms.
  • In an electrical autoclave, the electrical heater is used to generate heat directly, which is then transferred to the materials being sterilized. Electrical autoclaves may use infrared, conduction, or convection heating methods to transfer heat to the materials.
  • It is important to follow the manufacturer’s instructions for your specific autoclave and to use caution when working with steam or heat. Improper use of the steam generator or electrical heater can result in injury or damage to the materials being sterilized.

4. Vacuum generator (if applicable)

  • Vacuum System (If Applicable): All air inside the autoclave chamber must be replaced with steam to achieve proper sterilisation.
  • Particularly porous materials, such as animal bedding or fabric, or containers with limited apertures, such as flasks or bags, tend to retain air pockets after sterilisation. If an air pocket is present during the sterilisation cycle, any germs within the air pocket will survive and the items will not be sterile.
  • Due to this, many sterilisers incorporate a suction system. This not only enables the user to forcibly remove air by using a vacuum on the chamber before a cycle (known as pre-vacuum), but also to use a vacuum after the cycle (known as post-vacuum) to eliminate any remaining steam from the chamber and to dry the items within the autoclave.

5. Wastewater cooler

  • Before entering the drain piping, many autoclaves are fitted with a mechanism to cool the effluent (air, steam, and condensation).
  • Many localities and buildings prohibit effluent with a temperature above 140 F from entering the floor drain. Before it can be transported down the drain, the steam must be cooled to prevent damage to the facility’s drain piping.
  • The easiest way to cool this steam is to combine it with more cold tap water, however the quantity of water required can make an autoclave a significant contributor to a building’s water use. Some autoclaves include water-saving or even water-elimination technology.

6. Safety valve

The safety valve is a device that is designed to release pressure in the event that the pressure inside the autoclave becomes too high. This helps to prevent the autoclave from becoming over pressurized and potentially dangerous.

7. Control panel

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

8. Thermostatic Trap

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

autoclave diagram
autoclave diagram | Image Source: www.frankshospitalworkshop.com

Approximate Conditions for Autoclave sterilization

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

Autoclave Pressure and Temperature Chart

Steam autoclave 121 C (250 F)15psi15min
unwrapped items 132 C (270 F)30psi3min
lightly wrapped items 132 C (270 F)30psi8min
heavily wrapped items 132 C (270 F)30psi10min
Dry heat wrapped 170 C (340 F)
160 C (340 F)
150 C (300F)
140 C (285F)
121 C (250F)
60 min
Dry heat (rapid flow) unwrapped items190 C (375F)6min
Dry heat (rapid flow) packaged items190 C (375 F)12min
Ethylene oxide Ambient8-10 hours
Chemical vapor 132 C (270 F)20-40 psi20min
As published by Jada, (Journal of American Dental Association)

Autoclave Machine

Behind a successful steam sterilization, three important factors are responsible such as time, temperature, and steam quality. To fulfill these requirements there are 3 steps to the autoclave process such as:

  1. Conditioning Phase 
  • In the first phase of the sterilization cycle, the air must be removed from the autoclave by using the vacuum system. Otherwise, it will inhibit the sterilization.
  • The air can be removed from the autoclave by a series of steam flushes and pressure pulses.
  1. Exposure Phase
  • After that the lid is closed as a result the steam continuously increases with pressure and temperature. From here the exposure phase begins.
  • The item which is needed to be sterilized is held within the autoclave for a fixed amount of time.
  1. Exhaust Phase
  • At the final stage of sterilization, the lid is opened and releases the steam, depressurizing the vessel and allowing the items in the load to dry.

Quality steam is important to a successful autoclave sterilisation operation. The sterilising steam should consist of 97% steam (vapour) and 3% moisture (liquid water). This ratio is recommended for optimal heat transmission efficiency. When the moisture level of steam is below 3%, the steam is referred to as superheated (or dry). Superheated steam is useless for steam sterilisation because it is too dry for efficient heat transfer.

Operating Procedures of Autoclave

Wear personal protective equipment

  • Lab coat
  • Vision protection
  • Closed-toe footwear
  • Gloves resistant to heat to remove items, particularly hot glassware

Packaging and Loading

  1. Only authorised persons should be permitted to establish and/or modify autoclave parameters.
  2. Before using the autoclave, check inside for any potentially hazardous items left by the last user.
  3. Before loading the autoclave, the drain strainer should be thoroughly cleaned.
  4. Place goods in a secondary container at all times.
  5. Do not overburden or tightly bundle bags. Leave adequate space for steam circulation. If required, position the container on its side to enhance steam penetration and prevent air from becoming trapped.
  6. Use only autoclavable bags for waste packaging.
  7. To avoid plastic melting, do not allow bags to touch the internal walls of the autoclave.
  8. If the contents of the bag are dry, ensure that sufficient liquid is packed with them.
  9. Place contaminated glassware and laboratory equipment in secondary containers and autoclave using the solids cycle. Do not fill containers beyond the two-thirds mark with liquids. Use vented tops or loosen bottle caps.
  10. Before autoclaving clean glassware and wrapped instruments in the wrapped products cycle, place them in a secondary container.
  11. Use autoclave trays made of polypropylene, polycarbonate, or stainless steel for secondary containment. The trays should have a firm bottom and sides to prevent spills and contain the contents.
  12. Select the proper cycle for the material. Incorrect cycle selection may cause autoclave damage, liquid overflow, or bottle breakage.
  13. Start your cycle and fill out the user log for the autoclave. Typically, a cycle takes between 1 and 1.5 hours to complete.
  14. Check chamber/jacket pressure gauge for 20 pounds per square inch minimum pressure (psi).
  15. Lock and secure the door.
  16. Check the temperature of each load for 2500F (1210C).
  17. Do not open the door while the autoclave is in operation.


  1. Verify that the cycle has ended and the temperature and pressure have returned to safe levels.
  2. Wear the PPE outlined above in addition to an apron and face shield when removing liquids. As a precaution, stand back from the door and open it no more than 1 inch. This will allow residual steam to escape and adjust the pressure within liquids and containers.
  3. Allow the autoclaved load to rest in the chamber for 10 minutes. This will permit steam to dissipate and trapped air to escape from hot liquids, hence lowering operator risk.
  4. Do not shake or remove caps from superheated liquid containers prior to emptying.
  5. Place liquids in an area clearly marked “hot” until they have cooled to room temperature.
  6. Before transferring autoclaved goods, allow them to cool to ambient temperature. Never transfer goods that are overheated.
  7. Place the biohazard bag that has been autoclaved and cooled in the box for regulated medical waste. Infectious liquids that have been autoclaved may be disposed of in the sanitary sewer.

Which Materials You can Autoclave?

  • Glass: Glass \sOnly Pyrex® glass or Type I borosilicate glass can be autoclaved. When autoclaving liquids in Pyrex® containers, do not fill them above two-thirds capacity and do not seal them.
  • Plastic: Polypropylene is a low-cost, autoclave-temperature-resistant resin. Polypropylene containers are frequently utilised as secondary containers for autoclaved products. Additionally, polycarbonate can endure high temperatures. Under no circumstances are polystyrene (PS), polyvinyl chloride (PVC), nylon, acrylic, low-density polyethylene (LDPE), and high-density polyethylene (HDPE) lab ware and polyurethane tubing autoclavable.
  • Gloves: Gloves must be placed inside a biohazard bag that can be autoclaved and exposed to a steam setting; gloves will melt somewhat but will not catch fire.
  • Stainless steel: The majority of metals are suited for severe environments and sterilisation. Remove any plastics, liners, or other materials that could melt or catch fire.
  • Paper: Paper is combustible and should not be placed in an autoclave immediately. To prevent fire, it should be autoclaved in a waste bag using the biobag option.
  • Media Solution: No liquid should be autoclaved in a sealed container. Fill containers to two-thirds capacity and remove tops. They should be autoclaved in a cycle that generates steam.
  • Pipette tips: Most pipette tips are autoclavable. Some of these tips are made of plastic, while others are made of high density polyethylene. In general, pipette tips should only be placed in the autoclave as waste within a biohazard bag and should always be sterilised using a steam-producing mode.

Compatible/Incompatible Materials

Tissue Culture Flasks
Surgical Instruments
Pipette tips
Media Solutions
Animal food and bedding
Polypropylene (Secondary containers)
Stainless steel
Acids, bases and organic solvent
Chlorides, sulphates
Chlorine, hypochlorite, bleach
Non-stainless steel
Low density (LDPE) and High density polyethylene(HDPE)

Classification of Autoclave

There are four types of autoclave such as;

  1. Positive pressure displacement type (B-type): This type of autoclave can generate steam within seconds. They contain a separate steam generator, where steam is generated and then pass it into the autoclave.
  2. Negative pressure displacement type (S-type): This type of autoclave carries both the steam generator and a vacuum generator. The steam generator generates steam and then passes it into the autoclave. Vacuum generates pull out the air from the autoclave to create vacuum. This is the most expensive autoclave among all.
  3. Gravity displacement type autoclave: Gravity displacement type autoclave mainly used in laboratories. The steam generated inside the autoclave by a heating unit. It is cheaper than other types.
  4. Pressure cooker type/ Laboratory bench autoclaves (N-type): It contains an air and steam discharge tap, pressure gauge, and safety valve. This autoclave also contains an electric immersion heater at the bottom. The modern form of the autoclave contains a secure metal lid that can be fastened and sealed with a rubber gasket.
  5. Gravity autoclaves: Gravity autoclaves use steam that is introduced into the chamber through a series of tubes or pipes. The steam is heated to a high temperature and creates a high-pressure environment that is effective at killing microorganisms. Gravity autoclaves are typically the most affordable type of autoclave, but they may take longer to sterilize materials due to the relatively low pressure of the steam.
  6. Prevacuum autoclaves: Prevacuum autoclaves use steam that is introduced into the chamber through a series of tubes or pipes. The chamber is first evacuated to create a vacuum, and then steam is introduced. The vacuum helps to remove air from the chamber, which allows the steam to more effectively sterilize the materials. Prevacuum autoclaves are more efficient than gravity autoclaves, but they may be more expensive.
  7. Prevacuum displacement autoclaves: Prevacuum displacement autoclaves use steam that is introduced into the chamber through a series of tubes or pipes. The chamber is first evacuated to create a vacuum, and then steam is introduced. The vacuum helps to remove air from the chamber, which allows the steam to more effectively sterilize the materials. Prevacuum displacement autoclaves are similar to prevacuum autoclaves, but they have a built-in pump that helps to remove air from the chamber, which allows the steam to more effectively sterilize the materials.
Types of autoclave
Types of autoclave

Quality Control of Autoclave – Validation of Autoclave

A. Chemical Indicators

1. Tape Indicators

  • Tape indicators are self-adhesive paper tapes with heat-sensitive chemical indicators. When subjected to temperatures of 121°C, tape indicators change colour or display diagonal stripes, the words “sterile” or “autoclaved.”
  • Typically, tape indications are applied to the exterior of the trash load. The load is not deemed decontaminated if the temperature sensitive tape does not indicate that a temperature of at least 121°C was reached during the sterilising process.
  • Notify your department’s safety manager if tape indicators fail on two consecutive loads.
  • Tape indicators are neither designed nor intended to demonstrate that organisms have been effectively eliminated.
  • They signify that the autoclave temperature has reached 121 degrees Celsius. EHS advises that autoclave tape NOT be used as the sole sign of decontamination or sterilisation.

2. Integrated Chemical Indicator Strips

  • Integrated chemical indicator strips enable a limited validation of temperature and time by exhibiting a colour change following exposure to regular autoclave operation temperatures of 121 °C for several minutes.
  • Color-changing chemical markers can be put into the waste load. Notify your Department’s Safety Manager if the chemical indicators fail on two loads in a row.

B. Biological Indicators

Biological indicator vials contain spores of B. stearothermophilus, a bacterium that is rendered inactive when exposed to saturated steam at 121.1oC for at least 20 minutes. EHS will examine autoclaves used to treat biological waste quarterly using a biological indicator.


  1. EHS will coordinate tests for biological validity with laboratory personnel.
  2. EHS will incubate the indicators for 24 hours at 60°C alongside a control maintained at room temperature.


  • The validation will be repeated if the autoclaved indication demonstrates growth.
  • EHS will alert the Department Safety Manager and request service for the autoclave if the second validation indication fails. The autoclave should not be utilised until servicing has been performed and the validation test has been successfully completed.
  • The findings of validation tests are emailed by EHS personnel to the relevant labs and the Department Safety Manager.
  • Documentation of all validation testing is maintained by EHS.
Quality Control of Autoclave
Quality Control of Autoclave

Application of Autoclave

Autoclaves are commonly used in a variety of settings to sterilize materials and equipment. Some common applications of autoclaves include:

  1. Medical facilities: Autoclaves are commonly used in hospitals and other medical facilities to sterilize medical instruments, such as scalpels and forceps, and to sterilize materials, such as dressings and bandages.
  2. Dental offices: Autoclaves are used in dental offices to sterilize dental instruments and other equipment.
  3. Research laboratories: Autoclaves are commonly used in research laboratories to sterilize laboratory equipment, such as pipettes and Petri dishes, and to sterilize biological specimens.
  4. Industrial settings: Autoclaves are used in industrial settings to sterilize equipment and materials, such as tools and machinery.
  5. Food processing facilities: Autoclaves are used in food processing facilities to sterilize equipment and materials, such as containers and packaging materials.

Autoclaves are an essential tool in a variety of settings for ensuring that materials and equipment are free of microorganisms. It is important to follow the manufacturer’s instructions for your specific autoclave and to use caution when sterilizing materials to prevent injury or damage.


During operating an autoclave you should follow these following rules of precautions;

  1. Oil or powders like water proof or water-resistant substances can be used in autoclaves for sterilization.
  2. Don’t overload the autoclave, make sure there is sufficient space inside the autoclave.
  3. The materials needed to sterilize should always be placed in a secondary container.
  4. Avoid autoclave of a combustible substance such as paper. Palace them in a waste bag on a bio bag setting to prevent fire and then autoclave them.
  5. Avoid autoclave of flammable, reactive, corrosive, toxic or radioactive materials, household bleach, or paraffin-embedded tissue.
  6. Avoid the use of Plastic or polyethylene trays or containers they might melt and damage the autoclave.
  7. The water level within the containers should be 2/3rd of the total volume. It will prevent the spilling of the liquid.
  8. Never open the lid when the autoclave is working.
  9. Autoclave the waste materials and clean items separately.
  10. Use autoclavable bags to pack the wastes and items.

Sterilization control

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

Spores of Geobacillus Stearothermophilus (formerly called Bacillus Stearothermophilus) are the most reliable indicator because they resist steaming. The spores die within 12 minutes when temperatures reach 121 degrees Celsius. It is recommended that the Centers for Disease Control (CDC) suggests weekly autoclaving of an organism that has heat-resistant endospores from Geobacillus Stearothermophilus to test the effectiveness of autoclaves. The spore strip as well as the ampule of media contained inside a soft plastic vial are sold on the market. The vial is put in the middle of the material that is to be sterilized before being autoclaved. Then , the ampule inside is broken and the medium is released, and the entire container is then incubated. If there is no growth within the autoclaved cult, sterilization is considered efficient.

2. Autoclave tapes

Adhesive-backed tape that is chemical indicator markings which change the color of display-diagonal stripes or colors, with the wording “sterile” as well as “autoclaved” in the event of exposure to temperatures that are effective for sterilization (121degC) can be utilized to determine the effectiveness of autoclaves.

The tapes are placed in the middle of large packaging since heat absorption in these areas is guaranteed. (For instances, when the meat of a huge size is roasted, the outside is likely to be done, but the middle may remain unheated. And if the center is sufficiently heated , then it indicates that the desired temperature is reached). Autoclave tapes may not be 100% reliable as they don’t provide a time frame for how long the conditions were in place.

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

Thermocouple is a temperature-sensing device that measures temperature using the use of a potentiometer. The Browne’s Tube (invented in 1930 by Albert Browne in 1930) is made up of a red heat-sensitive dye that changes color after being exposed to a specific temperature for a specified period of time. The conversion of color information gives details about the time period and temperature.

Autoclave Cycles

For the autoclave to be successful, it must reach and maintain a temperature of 121° C for at least 30 minutes utilising saturated steam at a pressure of at least 15 psi. Depending on the composition and size of the load, a longer cycle time may be necessary.

The rate of exhaust will vary according on the characteristics of the load. Liquids and biological waste require slow exhaust to prevent boiling over of overheated liquids, whereas dry material can be treated with a rapid exhaust cycle.

Liquids Cycle

  • Use only glass containers with vented lids that are only two-thirds full.
  • Liquid media
  • Non flammable liquids
  • liquid organic waste
  • Aqueous solutions

Solids or Dry Cycle

  • Unwrapped or porous-packaged dry goods
  • Metals
  • Non-porous substances
  • empty wine glasses

Wrapped Goods or Pre-vacuum Cycle

  • Pipette tip packaging
  • Biohazardous waste contained in autoclave bags
  • Sterile glassware that must be sterilised vertically
  • Sharps disinfection

Advantages Autoclave

  1. High efficiency: Autoclaves are highly efficient at sterilizing materials and equipment, as the high temperatures and pressure of the steam are effective at killing microorganisms.
  2. Wide range of materials: Autoclaves can sterilize a wide range of materials, including metal, glass, and plastic.
  3. Easy to use: Autoclaves are relatively easy to use, and they typically have a control panel that allows the operator to set the temperature, pressure, and sterilization time.
  4. Safe: Autoclaves are generally safe to use when operated properly and according to the manufacturer’s instructions.

Disadvantages Autoclave

  1. Cost: Autoclaves can be expensive to purchase and maintain.
  2. Size and weight: Autoclaves are typically large and heavy, which can be a challenge in some settings.
  3. Risk of injury: If an autoclave is not used properly, there is a risk of injury, such as burns or cuts, from the steam or materials being sterilized.
  4. Limited materials: Some materials, such as sharp instruments or flammable materials, may not be suitable for sterilization in an autoclave.

Overall, autoclaves are a highly effective tool for sterilizing materials and equipment, but it is important to consider the advantages and disadvantages before purchasing an autoclave and to follow the manufacturer’s instructions for proper use.

Examples of Autoclave

Tuttnauer autoclave

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

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

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

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

Midmark autoclave

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

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

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

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

FAQ on Autoclave

1. What are autoclave bags made of?

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

2. Why are autoclave indicators used?

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

3. What are autoclave bags used for?

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

4. Can autoclave kill endospores?

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

5. Can autoclave kill prions?

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

6. How autoclave kill microorganisms?

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

how does an autoclave work

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

How does autoclaving kill bacteria?

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

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

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

How long does it take an autoclave to sterilize goods?

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

What temperature(s) can an autoclave reach?

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

How long do items stay sterile after autoclaving?

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

Further Reading


  • https://www.britannica.com/technology/autoclave
  • https://university.steris.com/course/understanding-steam-sterilization/
  • https://www.cdc.gov/hicpac/Disinfection_Sterilization/13_0Sterilization.html
  • https://www.cdc.gov/infectioncontrol/guidelines/disinfection/sterilization/steam.html
  • (ANSI) American National Standards Institute Inc./(AAMI) Association for the Advancement of Medical Instrumentation
  • https://blink.ucsd.edu/safety/research-lab/biosafety/autoclave/index.html
  • http://www.theratronics.ca/PDFs/Autoclave_Temperature_and_Time_Pressure_Chart.pdf
  • https://tuttnauer.com/blog/autoclave
  • https://en.wikipedia.org/wiki/Autoclave
  • https://consteril.com/how-does-a-laboratory-autoclave-work/


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