Autoclaves & Autoclave Bags – What You Need to Know


Sterilisation is imperative in a wide array of industries, particularly those where harmful microorganisms pose a risk to humans. These include medicine, dentistry, medical research, pharmaceutical development, and many more.

There are numerous methods of sterilisation, with autoclaving being one of these.

Autoclaves are machines used for high-heat sterilisation. They use steam delivered at high pressure over a prescribed time to kill spores and other potentially harmful microorganisms. Different patterns of heat, pressure, and vacuum are used to sterilise everything from dry goods to non-flammable and non-volatile liquids.

A Short History of the Autoclave Machine

The prototype of the modern pressure cooker (steam steriliser) was a steam digester invented in 1679 by French physicist Denis Papin. Two hundred years later, the first autoclave was created by French microbiologist Charles Chamberland, for specific use in medical applications.

1881 was the first time disinfection and sterilisation were formally researched when Robert Koch investigated how hot air and steam could kill germs, and he discovered the superiority for this purpose of moist heat (steam) when compared with dry heat.

The world’s first modern autoclave was the pressure steam steriliser, which was introduced in 1933. The technology developed over the following decades, with pre-vacuum cycles being invented in 1958 and the steam-flush pressure-pulse steriliser in 1987. Today, modern steam sterilisers or autoclaves are used in hospitals and other establishments globally.

How Does it Work?

The success of steam sterilisation in an autoclave requires three phases to be completed:

  1. Air must be removed from the chamber, as it inhibits sterilisation. This is usually affected by a vacuum system that uses pressure pulses and steam flushes.
  2. Upon the removal of all air, continuous steam is fed into the chamber until the pressure and temperature reach a prescribed level, depending on the material to be sterilised. These conditions are maintained for a fixed amount of time. The steam should be comprised of 97% vapour and 3% liquid water. Temperatures must reach between 121°C and 135°
  3. The exhaust phase involves the removal of the steam via the steriliser drain and the chamber is depressurised. The items within are allowed to dry.

What are Autoclave Bags?

Autoclave bags and sterilisation pouches are among the most important accessories used in autoclaving and instrument sterilisation.  

Autoclave bags consist of medical-grade paper and plastic film. These are bonded with an adhesive.

These single-use, disposable, peel-open bags are used at extreme temperatures and pressures in autoclave machines to kill microorganisms and spores on the objects placed inside of them. Used in high-heat sterilisation, they hold the items to be sterilised, protecting low-temperature plastics placed inside the bag and preventing these from clinging to the steriliser or autoclave sides. They also help to protect the integrity of the vent plumbing system within the steriliser.

Different types of sterilisation pouches are used depending on the type of autoclave used.

Five types of autoclaves each require a specific type of sterilisation bag:

  1. High Vacuum Steam Autoclave – polypropylene bag (up to 141°C)
  2. Gravity Steam Autoclave – polypropylene/polyethylene bags (up to 120°C)
  3. Chemical Vapour Autoclave – polypropylene bags (up to 141°C)
  4. Dry Heat Autoclaves – nylon bags (up to 160°C)
  5. Ethylene Oxide Gas (ETO Gas) Autoclave – polypropylene/polyethylene bags

Infectious materials should be autoclaved in clear or orange polyethylene plastic bags. These must be pliable, strong, and puncture-resistant. They should darken with use and show a clear biohazard symbol to demonstrate the correct sterilisation temperature.

 Autoclave bags are widely used in the:

  • Medical industry
  • Dental industry
  • Veterinary industry
  • Pharmaceutical industry
  • Scientific research labs
  • Tattooists
  • Professional piercers

Autoclave machines may be medical or industrial. They serve several purposes. These include but are not limited to:

  • Sterilisation of medical, dental, surgical, and research labware, tools, glassware, and other media including surgical instruments, implantable medical devices, and surgical linens and drapes.
  • Decontamination of biological waste.
  • Inactivation of organic materials, bacteria, viruses, parasites, and fungi before controlled medical waste is disposed of.
  • Liquid sterilisation in scientific and pharmacological labs.
  • Industrial processing of specialised rubbers or pressure-treated timbers.

Choosing Autoclavable Bags

The autoclave bag you use serves several objectives:

  1. Is compatible with the specific sterilisation process
  2. Allows adequate penetration of the sterilant
  3. The bag or pouch must be tamper-evident and non-resealable
  4. Maintain sterility of the contents until the package is opened
  5. Enable package opening without contamination by the user
  6. Contents must be sterile when used

The right autoclave bags for the dental and medical industry, for example, will be:

  • Self-sealing with a triple seal
  • Manufactured with medical-grade (non-recycled) paper
  • Use a transparent polypropylene laminate film of a minimum thickness of 2mm
  • Accommodate the required contents without crowding
  • Be impervious to sharps
  • Enable steam to enter the bag with controlled porosity
  • Have durable internal and external steam indicators
  • Transparent for easy viewing
  • Secure for containment and protection of contents during storage – the pores on the paper surface should close during the drying process
  • Prevent contamination after sterilisation
  • Clearly indicate (via colour change) on the exterior and interior of the pouch when it has been exposed to sterilisation processes
  • Be easy to label
  • Be easy to use and store
  • Be cost-effective

You need to understand the unique needs of the sterilisation processes for your industry and specific items and select the right autoclave bags to meet all of the abovementioned objectives.

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