Which sterilization method fits your load type?
Choosing the right sterilization process starts with understanding your load type. Laboratory waste, liquids, glassware, porous materials, and high-risk biological loads all behave differently during sterilization and therefore require specific cycles, temperatures, and handling methods.
Liquids
Culture media, reagents, or fluid discard
What is a fluid load?
Fluid (or liquid) loads typically consist of solutions or chemicals used in laboratory environments, such as growth media, but can include any non-solid material that requires sterilization. Growth or culture media may be solid, liquid, or semi-solid and are designed to support the growth of microorganisms or cells under controlled conditions. Different media are used for different cell types and must be sterilized before use, usually in an autoclave.
While many media are sterilized at 121 °C for 15 minutes, some require different temperatures or exposure times. For this reason, autoclaves used for media sterilization must be capable of operating across a range of temperatures and cycle parameters.
What type of fluid discard require sterilization?
Fluid discard loads include waste liquids that require sterilization before disposal:
- Used or expired culture media (such as nutrient broth)
- Reagents
- Liquid specimens
- Cleaning solutions
- Biological waste
How are sealed fluids sterilized?
Certain fluid loads require sterilization in sealed containers. In these cases, air removal by air purging (or “freesteaming”) is usually sufficient, and prolonged freesteaming is generally unnecessary. As with media preparation, processing speed is critical to maintaining product quality. Higher temperatures than 121 °C are often used to shorten sterilization times, and cooling times should be kept as short as possible.
Waste
What is a mixed discard load?
A mixed discard load consists of contaminated materials of varying types and forms that must be safely sterilized before disposal. This includes microbiological laboratory waste as well as clinical samples such as blood, tissue, and other biological materials.
Typical mixed discard loads may contain a combination of items, including:
- Plastic bags
- Containers
- Fabrics
- Gloves
- Paper towels
- Pipettes
- Culture plates
Because of the complexity and variety of materials involved, it is essential not to overfill the autoclave chamber. Overloading can prevent effective steam penetration and compromise sterilization. To ensure consistent and reliable results, multi-point (12-pen) validation is recommended.
For applications involving high-risk waste, Astell offers autoclave options compliant with Category III (BSL-3) requirements, including HEPA filtration and vacuum systems.
Why is sterilizing mixed discard loads tricky?
Mixed discard loads, which include a variety of materials in different types of containers, present unique sterilization challenges. One key issue is the presence of small pockets of trapped air, which can prevent effective steam penetration.
These loads are often placed in plastic bags and may include plastic containers that can melt or collapse before sterilization, increasing the risk of trapped air. For this reason, an advanced vacuum system is recommended to improve air removal.
We also advise using dedicated discard containers to contain spills and keep the autoclave chamber clean, ensuring safe and effective sterilization.
Glassware
Autoclaving scientific glassware ensures effective surface sterilization. A wide range of glass items are used in laboratory environments, and most require routine sterilization. Common examples include conical and volumetric flasks, beakers, test tubes, graduated cylinders, watch glasses, and similar items.
What types of glassware are recommended for autoclaving?
Borosilicate or quartz glassware is generally recommended, as these materials are better able to withstand the high temperatures and pressures encountered during autoclave cycles.
Which instruments are considered unwrapped instruments?
Unwrapped instruments typically include items used in medical, dental, veterinary, beauty, and ophthalmic procedures. This category may also include selected equipment used in laboratory experiments.
In some cases, larger items such as laboratory apparatus or metal cages must be sterilized. These are usually processed as unwrapped instruments to ensure effective sterilization.
Challenges of glassware and unwrapped instrument loads
Sterilizing glassware in an autoclave requires careful consideration to prevent breakage or shattering. Never seal empty glassware when using high-vacuum drying. Proper loading and unloading practices are essential to avoid damage, overcrowding, or the risk of scalding.
Of necessary, you can incorporate condensate removal and drying at the end of the cycle. All instrument loads benefit from post-cycle drying: unwrapped instruments are dried by heating the surrounding air, while glassware loads may require specialized drying procedures.
For small bench-top units, post-vacuum systems improve drying efficiency, whereas larger capacity units should use a jacketed pressure vessel to ensure optimal results.
Porous loads
What types of porous loads can be sterilized in an autoclave?
You can use autoclaves to sterilize a wide variety of fabrics and textiles. In hospitals, this often includes gowns, instrument packs, and other reusable items. Veterinary practices may use autoclaves to sterilize animal bedding, instruments, and similar materials.
Central Sterile Service Departments (CSSDs) typically use a combination of pouches and wrapping, depending on the size and type of surgical instruments being protected. Small instruments are usually placed in pouches, while larger items such as trays and pans are wrapped.
Surgical packs, wraps, and plain closure bags are commonly sealed with autoclave tape for added security. The tape changes color when it reaches the correct sterilization temperature, indicating successful sterilization. It is important to use proper autoclave tape, as substitutes such as masking tape cannot withstand autoclave conditions.
Hazardous waste
High-risk research
Biosafety Level 3 (BSL-3) facilities handle highly regulated work with harmful human pathogens, viruses, and bacteria that pose serious health and safety risks. Waste from these environments may contain hazardous microorganisms and must be effectively sterilized before disposal. Examples of microbes commonly handled in BSL-3 laboratories include Clostridium botulinum (botulism), yellow fever virus, and Mycobacterium tuberculosis.
In some cases, a double-door or “pass-through” autoclave is used. The loading (“dirty” or non-sterile) side is separated from the unloading (“clean” or sterile) side by a wall, often equipped with an SPF (bio) seal to prevent cross-contamination.
BSL-3 laboratories also require effluent retention systems, including bacteriological HEPA filters on exhausts, to prevent harmful pathogens from being released into the environment.
Why is sterilizing prions and other resistant microbes challenging?
For hazardous waste, a heated jacket is often used to ensure even temperature distribution within the vessel or chamber. Microorganisms become more active as temperatures rise, and while most are killed above 80 °C, some require higher temperatures and longer exposure times.
Prions, for example, demand significantly higher temperatures and extended cycles to achieve effective deactivation. Custom cycle settings may therefore be necessary to ensure that hazardous waste is thoroughly and safely sterilized.
How can we help you?
FAQ
What is considered a fluid load in an autoclave?
A fluid load includes any non-solid material that requires sterilization, such as growth media, reagents, or liquid waste.
Do all culture media require the same sterilization cycle?
Which types of fluids need to be sterilized before disposal?
What is a mixed discard load?
It’s a combination of contaminated materials, plastic bags, containers, gloves, paper towels, pipettes, culture plates, that must be sterilized before disposal.
Why is sterilizing mixed discard loads challenging?
These loads often trap air pockets, especially inside bags or plastic containers, preventing proper steam penetration.
Are special autoclaves needed for high‑risk waste
Yes. For BSL‑3 applications, autoclaves with HEPA filtration, vacuum systems, or Category III compliance are recommended.
What types of glassware are suitable for autoclaving?
Borosilicate and quartz glassware are recommended because they can tolerate high temperatures and pressure.
How are glassware and instruments dried after sterilization?
Unwrapped instruments dry through heated air. Glassware may require specialized drying or post‑vacuum systems (benchtop units) or jacketed vessels (large autoclaves).
What porous materials can be sterilized in an autoclave?
Textiles such as gowns, wraps, bedding, and reusable instrument packs.
How are surgical instruments typically packaged?
Small items go into pouches; larger trays and pans are wrapped.
What makes BSL‑3 waste different?
It may contain hazardous pathogens such as M. tuberculosis or yellow fever virus. Waste must be securely sterilized to prevent environmental release.
Why is sterilizing prions and highly resistant microbes difficult?
They require higher temperatures and significantly longer exposure times. Custom sterilization cycles are often necessary.