Autoclave sterilizer also known as steam sterilizers, and are typically used for healthcare or industrial applications. An autoclave is a machine that uses steam under pressure to kill harmful bacteria, viruses, fungi, and spores on items that are placed inside a pressure vessel. The items are heated to an appropriate sterilization temperature for a given amount of time. The moisture in the steam efficiently transfers heat to the items to destroy the protein structure of the bacteria and spores.

An autoclave is used in medical and laboratory settings to sterilize lab equipment and waste. Autoclave sterilization works by using heat to kill microorganisms such as bacteria and spores. The heat is delivered by pressurized steam. Pressurization allows the steam to reach the high temperatures that are required for sterilization.

According to Centers for Disease Control (CDC) Guidelines for Disinfection and Sterilization of Healthcare Facilities, pressurized steam is the most widely used and dependable method of sterilization. It’s nontoxic and inexpensive, it kills microbes and spores rapidly, and it quickly heats and penetrates fabrics.

According to manufacturer , medical clinics and dental offices typically use tabletop autoclaves, which are about the size of a microwave oven, while hospitals use much larger units that can sterilize many instruments at once.

The basic principle of steam sterilization, as accomplished in an autoclave, is to expose each item to direct steam contact at the required temperature and pressure for the specified time. Thus, there are four parameters of steam sterilization: steam, pressure, temperature, and time. The ideal steam for sterilization is dry saturated steam and entrained water (dryness fraction ≥97%).^{813, 819} Pressure serves as a means to obtain the high temperatures necessary to quickly kill microorganisms. Specific temperatures must be obtained to ensure the microbicidal activity. The two common steam-sterilizing temperatures are 121°C (250°F) and 132°C (270°F). These temperatures (and other high temperatures)⁸³⁰ must be maintained for a minimal time to kill microorganisms. Recognized minimum exposure periods for sterilization of wrapped healthcare supplies are 30 minutes at 121°C (250°F) in a gravity displacement sterilizer or 4 minutes at 132°C (270°F) in a prevacuum sterilizer (Table 7). At constant temperatures, sterilization times vary depending on the type of item (e.g., metal versus rubber, plastic, items with lumens), whether the item is wrapped or unwrapped, and the sterilizer type.

Autoclave sterilizer are commonly used in healthcare settings to sterilize medical devices. The items to be sterilized are placed inside a pressure vessel, commonly referred to as the chamber. Three factors are critical to ensuring successful steam sterilization in an autoclave: time, temperature and steam quality.

To meet these requirements there are three phases to the autoclave process:

1. Conditioning Phase (C): Air inhibits sterilization and must be removed from the chamber during the first phase of the sterilization cycle known as conditioning. In dynamic air removal-type steam sterilizers, the air can be removed from the chamber using a vacuum system. It can also be removed without a vacuum system using a series of steam flushes and pressure pulses. Gravity-type sterilizers use steam to displace the air in the chamber and force the air down the sterilizer drain.
2. Exposure Phase (S): After the air is removed, the sterilizer drain closes and steam is continuously admitted into the chamber, rapidly increasing the pressure and temperature inside to a predetermined level. The cycle enters the exposure phase and items are held at the sterilization temperature for a fixed amount of time required to sterilize them.
3. Exhaust Phase (E): During the final phase of the cycle, exhaust, the sterilizer drain is opened and steam is removed, depressurizing the vessel and allowing the items in the load to dry.

Quality steam is vital to a successful autoclave sterilization process. The steam used for sterilization should be composed of 97% steam (vapor) and 3% moisture (liquid water). This ratio is recommended for the most efficient heat transfer. When the steam moisture content is less than 3%, the steam is described as superheated (or dry). Superheated steam is too dry for efficient heat transfer and is ineffective for steam sterilization.

Commonly recommended temperatures for steam sterilization are 250° F (121° C), 270°F (132°C) or 275°F (135° C). To kill any microorganisms present, the items being sterilized must be exposed to these temperatures for the minimum time recommended by the manufacturer of the device being processed.

The exposure time is the time necessary to sterilize the device and does not include the entire cycle time. There is a time/temperature relationship for proper steam sterilization which has been developed by scientific testing and is used in all sterilization methods to create what is known as the total exposure phase. Exposure periods for steam sterilization vary with size, shape, weight, density and material composition of the device being sterilized, among other factors.

The exposure time is the time necessary to sterilize the device and does not include the entire cycle time. There is a time/temperature relationship for proper steam sterilization which has been developed by scientific testing and is used in all sterilization methods to create what is known as the total exposure phase. Exposure periods for steam sterilization vary with size, shape, weight, density and material composition of the device being sterilized, among other factors.

The size of the sterilizer will vary based on the capacity needed for the area where the autoclave will be used. For example, in a dental office the autoclave may simply sit on the countertop where the equipment only needs to sterilize small packs of instruments. An immediate-use sterilizer is typically needed near an operating room, and may only need to process 1-3 trays of instruments at a time. Most healthcare facilities, however, have large autoclave machines in their Sterile Processing Department (SPD) which can process 15-20 trays of instruments per cycle or even up to 625 lbs of instruments per cycle depending on size.

Industrial sized autoclaves for manufacturing processes can be very large, some comparable to the size of a semi-truck or airplane.

Autoclaves may be used in a variety of industrial and medical applications.

Industrial autoclaves are used in manufacturing environments to process parts and materials using heated steam and pressure: for example, in the manufacturing of pressure treated woods and specialized rubbers used in the tires of your car. Autoclaves are also used in the scientific research and pharmaceutical industries – beyond sterilizing equipment used in laboratory research most autoclaves come equipped with a liquid cycle to sterilize liquids used in laboratory environments.

Medical steam sterilizers are used in healthcare environments for the sterilization of heat and moisture-stable items such as surgical instruments, implanted medical devices and surgical drapes and linens. The cycles used in medical steam sterilizers are developed and validated according to recognized industry standards. In the United States, steam sterilizers used in healthcare must be cleared for use by the Food and Drug Administration for the sterilizer manufacturer’s stated intended use.