
An autoclave is a machine used to carry out industrial and scientific processes requiring elevated temperature and pressure in relation to
ambient pressure
The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, in contact with the object.
Atmosphere
Within the atmosphere, the ambient pressure decreases as elevation increases. By measuring ambient atmosp ...
and/or
temperature
Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
. Autoclaves are used before surgical procedures to perform
sterilization
Sterilization may refer to:
* Sterilization (microbiology), killing or inactivation of micro-organisms
* Soil steam sterilization, a farming technique that sterilizes soil with steam in open fields or greenhouses
* Sterilization (medicine) render ...
and in the chemical industry to cure coatings and
vulcanize
Vulcanization (British English: vulcanisation) is a range of processes for hardening rubbers. The term originally referred exclusively to the treatment of natural rubber with sulfur, which remains the most common practice. It has also grown to ...
rubber and for
hydrothermal synthesis
Hydrothermal synthesis includes the various techniques of synthesizing substances from high-temperature aqueous solutions at high pressures; also termed "hydrothermal method". The term "hydrothermal" is of geologic origin. Geochemists and mine ...
. Industrial autoclaves are used in industrial applications, especially in the manufacturing of composites.
Many autoclaves are used to sterilize equipment and supplies by subjecting them to pressurized
saturated steam
Steam is water vapor, often mixed with air or an aerosol of liquid water droplets. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Saturated or superheated steam is ...
at for 30–60 minutes at a gauge pressure of 103 kPa depending on the size of the load and the contents. The autoclave was invented by
Charles Chamberland
Charles Edouard Chamberland (; 12 March 1851 – 2 May 1908) was a French microbiologist from Chilly-le-Vignoble in the department of Jura who worked with Louis Pasteur. Chamberland was present at Pouilly-le-Fort when the efficacy of the anthr ...
in 1879,
although a precursor known as the
steam digester
The steam digester or bone digester (also known as Papin’s digester) is a high-pressure cooker invented by French physicist Denis Papin in 1679. It is a device for extracting fats from bones in a high-pressure steam environment, which also rend ...
was created by
Denis Papin
Denis Papin FRS (; 22 August 1647 – 26 August 1713) was a French physicist, mathematician and inventor, best known for his pioneering invention of the steam digester, the forerunner of the pressure cooker, the steam engine, the centrifug ...
in 1679.
The name comes from Greek ''auto-'', ultimately meaning self, and Latin ''clavis'' meaning key, thus a self-locking device.
Uses
Sterilization autoclaves are widely used in
microbiology
Microbiology () is the branches of science, scientific study of microorganisms, those being of unicellular organism, unicellular (single-celled), multicellular organism, multicellular (consisting of complex cells), or non-cellular life, acellula ...
and
mycology
Mycology is the branch of biology concerned with the study of fungus, fungi, including their Taxonomy (biology), taxonomy, genetics, biochemistry, biochemical properties, and ethnomycology, use by humans. Fungi can be a source of tinder, Edible ...
,
medicine
Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...
and
prosthetics
In medicine, a prosthesis (: prostheses; from ), or a prosthetic implant, is an artificial device that replaces a missing body part, which may be lost through physical trauma, disease, or a condition present at birth (congenital disorder). Prosthe ...
fabrication,
tattooing
A tattoo is a form of body modification made by inserting tattoo ink, dyes, or pigments, either indelible or temporary, into the dermis layer of the Human skin, skin to form a design. Tattoo artists create these designs using several Process of ...
and
body piercing, and
funerary practice. They vary in size and function depending on the media to be sterilized and are sometimes called
retort
In a chemistry laboratory, a retort is a device used for distillation or dry distillation of substances. It consists of a sphere, spherical vessel with a long downward-pointing neck. The liquid to be distilled is placed in the vessel and heat ...
in the chemical and food industries.
Typical loads include laboratory glassware, other equipment and waste, surgical instruments, and
medical waste
Biomedical waste or hospital waste is any kind of waste containing infectious (or potentially infectious) materials generated during the treatment of humans or animals as well as during research involving biologics. It may also include waste ass ...
.
A notable recent and increasingly popular application of autoclaves is the pre-disposal treatment and sterilization of waste material, such as pathogenic hospital waste.
Machines in this category largely operate under the same principles as conventional autoclaves in that they are able to neutralize (but not eliminate) potentially infectious agents by using pressurized steam and superheated water.
Autoclaves are also widely used to cure composites, especially for melding multiple layers without any voids that would decrease material strength, and in the vulcanization of rubber.
The high heat and pressure that autoclaves generate help to ensure that the best possible physical properties are repeatable. Manufacturers of spars for sailboats have autoclaves well over long and wide, and some autoclaves in the aerospace industry are large enough to hold whole airplane fuselages made of layered composites.
A thermal
effluent decontamination system
An effluent decontamination system (EDS) is a device, or suite of devices, designed to decontaminate or Sterilization (microbiology), sterilise biologically active or biohazardous materials in fluid and liquid waste material. Facility types that m ...
functions as a single-purpose autoclave designed for the sterilization of liquid waste and effluent.
Air removal
It is very important to ensure that all of the trapped air is removed from the autoclave before activation, as trapped air is a very poor medium for achieving sterility. Steam at can achieve a desired level of sterility in three minutes, while achieving the same level of sterility in hot air requires two hours at . Methods of air removal include:
;
Downward displacement (or gravity-type):: As steam enters the chamber, it fills the upper areas first as it is less dense than air. This process compresses the air to the bottom, forcing it out through a drain which often contains a temperature sensor. Only when air evacuation is complete does the discharge stop. Flow is usually controlled by a
steam trap
A steam trap is a device used to discharge condensates and non-condensable gases with a negligible consumption or loss of live steam. Steam traps are nothing more than automatic valve
A valve is a device or natural object that regulates, d ...
or a
solenoid valve
A solenoid valve is an electromechanically operated valve.
Solenoid valves differ in the characteristics of the electric current they use, the strength of the magnetic field they generate, the mechanism they use to regulate the fluid, and the ...
, but bleed holes are sometimes used. As the steam and air mix, it is also possible to force out the mixture from locations in the chamber other than the bottom.
;
Steam pulsing:: Air dilution by using a series of steam pulses, in which the chamber is alternately pressurized and then depressurized to near atmospheric pressure.
;
Vacuum pump
A vacuum pump is a type of pump device that draws gas particles from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke, and was preceded by the suction pump, which dates to ...
s
:: A vacuum pump sucks air or air/steam mixtures from the chamber.
;
Superatmospheric cycles:: Achieved with a vacuum pump. It starts with a vacuum followed by a steam pulse followed by a vacuum followed by a steam pulse. The number of pulses depends on the particular autoclave and cycle chosen.
;
Subatmospheric cycles:: Similar to the superatmospheric cycles, but chamber pressure never exceeds atmospheric pressure until they pressurize up to the sterilizing temperature.
Stovetop autoclaves used in poorer or non-medical settings do not always have automatic air removal programs. The operator is required to manually perform steam pulsing at certain pressures as indicated by the gauge.
In medicine
A medical autoclave is a device that uses
steam
Steam is water vapor, often mixed with air or an aerosol of liquid water droplets. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Saturated or superheated steam is inv ...
to
sterilize equipment and other objects. This means that all
bacteria
Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...
,
virus
A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...
es,
fungi
A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
, and
spore
In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
s are inactivated. However,
prion
A prion () is a Proteinopathy, misfolded protein that induces misfolding in normal variants of the same protein, leading to cellular death. Prions are responsible for prion diseases, known as transmissible spongiform encephalopathy (TSEs), w ...
s, such as those associated with
Creutzfeldt–Jakob disease
Creutzfeldt–Jakob disease (CJD) is an incurable, always fatal neurodegenerative disease belonging to the transmissible spongiform encephalopathy (TSE) group. Early symptoms include memory problems, behavioral changes, poor coordination, visu ...
, and some toxins released by certain bacteria, such as
Cereulide
Cereulide is a toxin produced by some strains of ''Bacillus cereus'', ''Bacillus megaterium'' and related species. It is a potent cytotoxin that destroys mitochondria. It causes nausea and vomiting.
Cereulide acts as ionophore with a high affinit ...
, may not be destroyed by autoclaving at the typical 134 °C for three minutes or 121 °C for 15 minutes and instead should be immersed in sodium hydroxide (1M NaOH) and heated in a gravity displacement autoclave at 121 °C for 30 min, cleaned, rinsed in water and subjected to routine sterilization.
Although a wide range of
archaea
Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...
species, including ''
Geogemma barossii (Strain 121)'', can survive and even reproduce at temperatures found in autoclaves, their growth rate is so slow at the lower temperatures in the less extreme environments occupied by humans that it is unlikely they could compete with other organisms. None of them are known to be infectious or otherwise pose a health risk to humans; in fact, their biochemistry is so different from that of humans, and their multiplication rate is so slow, that microbiologists need not worry about them.
Autoclaves are found in many medical settings, laboratories, and other places that need to ensure the sterility of an object. Many procedures today employ single-use items rather than sterilizable, reusable items. This first happened with
hypodermic needles, but today many
surgical instruments
A surgical instrument is a medical device for performing specific actions or carrying out desired effects during a surgery or operation, such as modifying biological tissue, or to provide access for viewing it. Over time, many different kinds of ...
(such as
forceps
Forceps (: forceps or considered a plural noun without a singular, often a pair of forceps; the Latin plural ''forcipes'' is no longer recorded in most dictionaries) are a handheld, hinged instrument used for grasping and holding objects. Forcep ...
,
needle holders, and
scalpel
A scalpel or bistoury is a small and extremely sharp bladed instrument used for surgery, anatomical dissection, podiatry and various handicrafts. A lancet is a double-edged scalpel.
Scalpel blades are usually made of hardened and tempered ...
handles) are commonly single-use rather than reusable items (see
waste autoclave
A waste autoclave is a form of solid waste treatment that uses heat, steam and pressure of an industrial autoclave in the processing of waste. Waste autoclaves process waste either in batches or in continuous-flow processes. In batch processes ...
).
Because
damp heat is used,
heat-labile
Lability refers to the degree that something is likely to undergo change. It is the opposite (antonym) of stability.
Biochemistry
In reference to biochemistry, this is an important concept as far as kinetics is concerned in metalloproteins. ...
products (such as some
plastics
Plastics are a wide range of synthetic or semisynthetic materials composed primarily of polymers. Their defining characteristic, plasticity, allows them to be molded, extruded, or pressed into a diverse range of solid forms. This adaptab ...
) cannot be sterilized this way or they will melt.
Paper
Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses, Feces#Other uses, herbivore dung, or other vegetable sources in water. Once the water is dra ...
and other products that may be damaged by steam must also be sterilized another way. In all autoclaves, items should always be separated to allow the steam to penetrate the load evenly.
Autoclaving is often used to sterilize medical waste prior to disposal in the standard
municipal solid waste
Municipal solid waste (MSW), commonly known as trash or garbage in the American English, United States and rubbish in British English, Britain, is a List of waste types, waste type consisting of everyday items that are discarded by the public. ...
stream. This application has become more common as an alternative to
incineration
Incineration is a waste treatment process that involves the combustion of substances contained in waste materials. Industrial plants for waste incineration are commonly referred to as waste-to-energy facilities. Incineration and other high ...
due to environmental and health concerns about the combustion by-products emitted by incinerators, especially from the small units which were commonly operated at individual hospitals. Incineration or a similar thermal oxidation process is still generally mandated for pathological waste and other very toxic or infectious medical waste. For liquid waste, an
effluent decontamination system
An effluent decontamination system (EDS) is a device, or suite of devices, designed to decontaminate or Sterilization (microbiology), sterilise biologically active or biohazardous materials in fluid and liquid waste material. Facility types that m ...
is the equivalent hardware.
In dentistry, autoclaves provide sterilization of dental instruments.
In most of the industrialized world
medical-grade
A biomaterial is a substance that has been engineered to interact with biological systems for a medical purpose – either a therapeutic (treat, augment, repair, or replace a tissue function of the body) or a diagnostic one. The corresponding f ...
autoclaves are regulated
medical devices
A medical device is any device intended to be used for medical purposes. Significant potential for hazards are inherent when using a device for medical purposes and thus medical devices must be proved safe and effective with reasonable assura ...
. Many medical-grade autoclaves are therefore limited to running regulator-approved cycles. Because they are optimized for continuous hospital use, they favor rectangular designs, require demanding maintenance regimens, and are costly to operate. (A properly calibrated medical-grade autoclave uses thousands of gallons of water each day, independent of task, with correspondingly high electric power consumption.)
In research
Autoclaves are used in education, research, biomedical research, pharmaceutical research and industrial settings to sterilize lab instruments and glassware, process waste loads prior to disposal, prepare culture media and liquid media, and artificially age materials for testing.
Although autoclaves produced for use in medicine may be used in research settings, labs may opt for "research-grade" autoclaves. These are specifically designed for non-medical applications. Research autoclaves often use a “jacketless” design where steam is generated directly in the pressure chamber using heating coils (rather than relying on a “steam jacket” and independent steam generator, as is the case in high-throughput medical autoclaves). Research-grade autoclaves do not have to meet stringent requirements associated with sterilizing instruments that will be directly used on humans. Instead they can prioritize efficiency, programming flexibility, ease-of-use, and sustainability.
In 2016, the Office of Sustainability at the University of California, Riverside (UCR) conducted a study of autoclave efficiency in their genomics and entomology research labs, tracking several units' power and water consumption. They found that, even when functioning within intended parameters, the medical-grade autoclaves used in their research labs were each consuming 700 gallons of water and 90 kWh of electricity per day (1,134MWh of electricity and 8.8 million gallons of water per year), because they consumed energy and water continuously, even when not in use. UCR's research-grade autoclaves performed the same tasks with equal effectiveness, but used 83% less energy and 97% less water.
The
University of Alabama at Birmingham
The University of Alabama at Birmingham (UAB) is a public research university in Birmingham, Alabama, United States. Founded in 1969 and part of the University of Alabama System, UAB has grown to be the state's largest employer, with more than ...
(UAB) completed a similar study in 2023 in order to assess the performance differences between similar-sized jacketed and non-jacketed autoclaves performing identical tasks in a research setting. They monitored side-by-side autoclaves in a facility running cycles indicative of the most common load and sterilization tasks used by their researchers campuswide. UAB found that jacketed autoclaves consumed significantly more water (44–50 gallons per cycle) and house steam (25–41 pounds per cycle) than non-jacketed autoclaves, which used less than 2 gallons of water and no house steam per cycle, regardless of cycle type or task. The higher water use by jacketed autoclaves resulted in an estimated water cost of $764 per jacketed autoclave per year, compared to $23 for non-jacketed autoclaves. With over 100 steam-jacketed autoclaves on campus, the author calculated that using jacketed autoclaves for research tasks translated into an additional $74,000 in annual excess spending for UAB. In addition, jacketed autoclaves had a higher initial purchase price than non-jacketed equivalents (37% more). The author also noted anecdotal reports of electrical utility and maintenance cost savings associated with non-jacketed autoclaves.
Research autoclaves display a wide range of designs and sizes, and are frequently tailored to their use and load type. Common variations include either a cylindrical or square pressure chamber, air- or water-cooling systems, and vertically or horizontally opening chamber doors (which may be electrically or manually powered). Research-grade autoclaves may be configured for "pass-through" operation. This makes it possible to maintain absolute isolation between "clean" and potentially contaminated work areas. Pass-through research autoclaves are especially important in
BSL-3 or
BSL-4 facilities.
Quality assurance
In order to sterilize items effectively, it is important to use optimal parameters when running an autoclave cycle. A 2017 study performed by the
Johns Hopkins Hospital
Johns Hopkins Hospital (JHH) is the teaching hospital and biomedical research facility of Johns Hopkins School of Medicine in Baltimore, Maryland. Founded in 1889, Johns Hopkins Hospital and its school of medicine are considered to be the foundin ...
biocontainment
One use of the concept of biocontainment is related to laboratory biosafety and pertains to microbiology laboratories in which the physical containment of pathogenic organisms or agents (bacteria, viruses, and toxins) is required, usually by is ...
unit tested the ability of pass-through autoclaves to
decontaminate
Decontamination (sometimes abbreviated as decon, dcon, or decontam) is the process of removing contaminants on an object or area, including chemicals, micro-organisms, and/or radioactive substances. This may be achieved by chemical reaction, dis ...
loads of simulated
biomedical waste
Biomedical waste or hospital waste is any kind of waste containing Infection, infectious (or potentially infectious) materials generated during the treatment of humans or animals as well as during research involving biologics. It may also include ...
when run on the factory default setting. The study found that 18 of 18 (100%) mock patient loads (6 PPE, 6 linen, and 6 liquid loads) passed sterilization tests with the optimized parameters compared to only 3 of 19 (16%) mock loads that passed with use of the factory default settings.
There are physical, chemical, and biological indicators that can be used to ensure that an autoclave reaches the correct temperature for the correct amount of time. If a non-treated or improperly treated item can be confused for a treated item, then there is the risk that they will become mixed up, which, in some areas such as surgery, is critical.
Chemical indicator
A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. Hence, ...
s on medical packaging and
autoclave tape change color once the correct conditions have been met, indicating that the object inside the package, or under the tape, has been appropriately processed. Autoclave tape is only a marker that steam and heat have activated the dye. The marker on the tape does not indicate complete sterility. A more difficult challenge device, named the Bowie-Dick device after its inventors, is also used to verify a full cycle. This contains a full sheet of chemical indicator placed in the center of a stack of paper. It is designed specifically to prove that the process achieved full temperature and time required for a normal minimum cycle of 134 °C for 3.5–4 minutes.
To prove sterility, biological indicators are used. Biological indicators contain
spores
In biology, a spore is a unit of sexual (in fungi) or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plant ...
of a heat-resistant bacterium, ''
Geobacillus stearothermophilus
''Geobacillus stearothermophilus'' (previously ''Bacillus stearothermophilus'') is a rod-shaped, Gram-positive bacterium and a member of the phylum Bacillota. The bacterium is a thermophile and is widely distributed in soil, hot springs, ocean se ...
''. If the autoclave does not reach the right temperature, the spores will
germinate
Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an flowering plant, angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the sp ...
when incubated and their
metabolism
Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...
will change the color of a
pH-sensitive chemical. Some physical indicators consist of an
alloy
An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...
designed to melt only after being subjected to a given temperature for the relevant holding time. If the alloy melts, the change will be visible.
Some computer-controlled autoclaves use an F
0 (F-nought) value to control the
sterilization
Sterilization may refer to:
* Sterilization (microbiology), killing or inactivation of micro-organisms
* Soil steam sterilization, a farming technique that sterilizes soil with steam in open fields or greenhouses
* Sterilization (medicine) render ...
cycle. F
0 values are set for the number of minutes of sterilization equivalent to at above atmospheric pressure for 15 minutes. Since exact temperature control is difficult, the temperature is monitored, and the sterilization time adjusted accordingly.
Additional images
Image:Autoclave stove top.jpg, Stovetop autoclaves, also known as pressure cooker
A pressure cooker is a sealed vessel for cooking food with the use of high pressure steam and water or a water-based liquid, a process called pressure cooking. The high pressure limits boiling and creates higher temperatures not possible at low ...
—the simplest of autoclaves
File:Autoclave machine.jpg, The machine on the right is an autoclave used for processing substantial quantities of laboratory equipment prior to reuse, and infectious material prior to disposal. (The machines on the left and in the middle are washing machines.)
File:Systec H-Series Autoclaves.jpg, Horizontal high-capacity autoclave with cylindrical chamber
File:Pass-through-autoclaves-1-231x300.jpg, Illustration of a cylindrical-chamber pass-through autoclave
References
External links
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{{Authority control
Laboratory equipment
Medical equipment