Autoclave Sterilizer Machine

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.

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Basic Principle Of Steam Sterilization?

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.

How Does An Autoclave Sterilizer Work?

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.

Types Of Autoclave Sterilizer And Their Advantages

Autoclaves function primarily through either gravity or vacuum-induced or pre-vacuum (pre vac) sterilization methods, though some types of autoclaves combine both methods to sterilize. Though both types of autoclaves sterilize through high-temperature steam and use pressure as a means to allow steam to displace ambient air in the chamber to penetrate sterilization media, how these mechanisms occur differ and thus, are more conducive to certain types of media over others.

Gravity autoclaving, also known as gravity displacement autoclaving is the most basic form and is suitable for sterilizing the most common laboratory media, including steel utensils, glassware, and bio-hazardous waste. Gravity-induced autoclaving involves pumping steam into the autoclave chamber, which displaces the ambient air and forces it out of exhaust valves so that the remaining steam can sterilize the contents. This mechanism is advantageous in the simplicity of its design and lack of dependency on peripheral mechanisms to displace ambient air with steam, making these types of autoclaves more affordable and dependable. The majority of autoclave media or items to be sterilized are simple in design and do not contain spaces or obstacles for steam to penetrate within, thus the steam displacement function is ample for proper sterilization.  It is for these reasons that gravity autoclaves are the most common types of autoclaves in the market and are usually the recommended type of autoclave for most uses.

On the other hand, vacuum autoclaving, also known as pre-vacuum autoclaving or sterilizing is more suited in cases where air cannot be easily removed from sterilization media.  This may include large or porous items such as animal cages and bedding sterilization as well as wrapped surgical kits.  The vacuum function in these autoclaves allows deeper sterilization of the contents, as it completely evacuates the ambient air within, allowing high-temperature steam to penetrate and sterilize areas that would normally be occupied by ambient air, and can be more efficient at sterilizing certain items with hard-to-reach areas within.

Autoclave Media & the Appropriate Autoclave Type

As mentioned above, your choice of an autoclave system largely depends on your autoclave media, ie. the items to be sterilized.  Overall, steam sterilization is highly dependable, effective, fast, and non-toxic, and offers an inexpensive way to rapidly heat and penetrate the chamber’s contents, including appropriately contained liquids.  However, this method cannot sterilize powders or oils, and can only work with heat and moisture-resistant goods.  Keeping this in mind, below is a summary of the primary types of media used by gravity and vacuum-autoclave types.

Gravity autoclaves are appropriate for sterilizing non-porous items (i.e. those with a hard surface):

  • Most metals, particularly stainless steel surgical instruments and lab utensils
  • Polypropylene Pyrex® or Type I borosilicate glassware
  • Biohazard waste
  • Unwrapped goods

Vacuum (pre and post) are appropriate for sterilizing large or porous items:

  • Media solutions in appropriate containers, such as tissue culture flasks with loose caps for a steam autoclave cycle
  • Pipette tips and other high-density polyethylene products, such as syringes
  • Wrapped dry items that can trap air
  • Animal cages and bedding
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Choosing an Autoclave

Choosing the right autoclave for your purposes requires you to not only assess the type of media to autoclave, but also throughput capacity, available lab space, and access to utilities including electricity (with proper power output), water and house steam.

Due to the simplicity of the gravity-displacement mechanism, which requires an autoclaving chamber, a heating mechanism, intake and exhaust valves, there is great flexibility in design for gravity autoclaves, including front and top-loading types.

The top-loading type autoclave is particularly advantageous, as it allows for maximum loading space, minimum floor space requirement and does not require any building steam connection, as the vertical chamber design allows for water to rest at the bottom, which in turn is turned into steam through a heating element located at the bottom. Note that many autoclaves on the market, especially compact top-loading autoclaves often require no more than access to the proper electrical outlet type and enough space to place your autoclave.

Gravity autoclaves are also particularly advantageous when used in geographical areas of high humidity or higher altitudes as they consistently retain the relationship between pressure and heat within the autoclave chamber and overcome differences in boiling points at higher altitudes by opening and closing the exhaust valve.  Known as high altitude autoclaves, their functions allow for proper sterilization to occur in laboratories and hospitals located in markets with high altitude terrains.

Regarding the size of your autoclave, to limit energy use and costs especially for smaller labs, it is important to buy the proper size autoclave that will accommodate the equipment that needs sterilizing, while not going overcapacity. For this, several autoclaves range between 50 L and 70 L, which tend to strike a good balance between relatively high capacity and low energy use.

What is the temperature for autoclave 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.

How long does it take an autoclave to sterilize?

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.

How long does it take an autoclave to sterilize?

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.

How Big Is An Autoclave?

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.

Industrial Autoclaves VS. Medical Autoclaves

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.

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