Autoclave
An autoclave is a machine used to carry out industrial and scientific processes requiring elevated temperature and pressure in relation to ambient pressure and temperature. Autoclaves are found in many medical settings, laboratories, and other places that need to ensure the sterility of an object.
The autoclave was invented by Charles Chamberland in 1879, although a precursor known as the steam digester was created by Denis Papin in 1679. The name comes from Greek auto-, meaning "self", and Latin clavis meaning "key", thus a self-locking device. All autoclaves operate according to the same fundamental principles as a kitchen pressure cooker. The simplest autoclaves are largely indistinguishable from pressure cookers used in food preparation.
Autoclaves are most commonly used before surgical procedures to sterilize medical instruments and supplies. This is accomplished by subjecting these items to pressurized saturated steam at at a gauge pressure of for 15 to 60 minutes, depending on the size, density, and contents of the load.
Industrial autoclaves are used in industrial applications, especially in the manufacturing of composites. Autoclaves are also commonly used in the chemical industry to cure coatings, vulcanize rubber, and for hydrothermal synthesis. Flexible "research-grade" autoclaves are used in a wide range of research and industrial tasks, including quality control and quality assurance for food and beverage production, biomedical and pharmaceutical research and development, and product testing.
Uses
Sterilization autoclaves are widely used in microbiology and mycology, medicine and prosthetics fabrication, tattooing and body piercing, and funerary practice, and a wide range of industries. Autoclaves vary in size and function depending on the media to be sterilized. They are sometimes called retorts in the chemical and food industries. Typical loads include laboratory glassware, growth media, other equipment, surgical instruments, and potentially pathogenic waste.A notable recent and increasingly popular application of autoclaves is the pre-disposal treatment and sterilization of waste material, such as pathogenic medical waste. Machines in this category largely operate under the same principles as conventional autoclaves in that they are able to neutralize potentially infectious agents by using pressurized steam and superheated water. A thermal effluent decontamination system functions as a single-purpose autoclave designed for the sterilization of liquid waste and effluent.
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.
Air removal
It is very important to ensure that all of the trapped air is removed from the load prior to beginning the sterilization cycle, 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:;
;
;Vacuum pumps
;
;
Stovetop autoclaves used in poorer or non-medical settings rarely 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 to sterilize equipment and other objects. This means that all bacteria, viruses, fungi, and spores are inactivated. However, prions, such as those associated with Creutzfeldt–Jakob disease, and some toxins released by certain bacteria, such as Cereulide, 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 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 species, including Geogemma barossii , 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. Their biochemistry is so different from that of humans, and their multiplication rate is so slow, that microbiologists need not worry about them.Because damp heat is used, heat-labile products cannot be sterilized this way or they will melt. Paper 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.
Many procedures today employ single-use items rather than sterilizable, reusable items. This first happened with hypodermic needles, but today many surgical instruments are commonly single-use rather than reusable items.
Autoclaving is often used to sterilize medical waste prior to disposal in the standard municipal solid waste stream. This application has become more common as an alternative to incineration 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 often mandated for pathological waste and other very toxic or infectious medical waste. For liquid waste, an effluent decontamination system is the equivalent hardware.
In most of the industrialized world medical-grade autoclaves are regulated medical devices. 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.
In research
Autoclaves are used in research and education to sterilize lab instruments and glassware, process waste loads prior to disposal, prepare culture media and liquid media, and artificially age materials for testing. They play a prominent role in biomedical research, pharmaceutical research, and industrial R&D. Research autoclaves display a wide range of designs and sizes, and may be tailored to their use and load type. Common variations include either a cylindrical or square pressure chamber, air- or water-cooling systems, air-ballast systems, and vertically or horizontally opening chamber doors. 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.Autoclaves not intended for use in a medical setting may be referred to as "research-grade" autoclaves. These are specifically designed for non-medical applications. Research autoclaves use a “jacketless” design where steam is generated directly in the pressure chamber using heating coils. 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.
The added cost of using a medical autoclave in a non-medical setting can be significant. For a 2016 study, the Office of Sustainability at the University of California, Riverside tracked the power and water consumption of medical-grade and research-grade autoclaves performing similar research-related tasks. Even when functioning within intended parameters, the medical-grade autoclaves consumed 700 gallons of water and 90 kWh of electricity per day. 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 completed a similar study in 2023 comparing similar-sized jacketed and non-jacketed autoclaves performing identical cycles indicative of the most common load and sterilization tasks used by their researchers. UAB found that jacketed autoclaves consumed significantly more water and house steam than non-jacketed autoclaves, which used less than 2 gallons of water and no house steam per cycle. 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. Jacketed autoclaves also had a higher initial purchase price.