What are they and what do they do
Autoclaves are one of the most common Sterilisation tools, widely used in laboratories, hospitals, and pharmaceutical manufacturing. They provide an effective way to eliminate microbial contamination.
Autoclaves are used for a variety of Sterilisation requirements, for example:
- Terminal Sterilisation, sterilising product after manufacture
- Sterilisation of tools/pipes to be used in a sterile assembly such as filling line
- Sterilisation of components such as Stoppers
- Biohazard waste disposal to sterilise contaminated lab waste
How Autoclaves Work: The Power of Steam
Autoclaves use Saturated Steam to release Latent heat over the load surfaces, this energy is enough to destroy any bacteria, viruses, and spores. This contact energy sterilises surfaces brilliantly, certain processes require a pasteurisation style approach, such as Terminal Sterilisation, where heat is required to penetrate the whole system rather than surface sterilisation. Due to the fact air is a very poor conductor, air must first be removed from the entire system to ensure no blind spots in the load where bacteria can be allowed to survive.
Autoclaves are a textbook example of Moist heat sterilisation, this is a great Sterilisation method but means that loads can’t compromise of parts that damage under heat such as plastic or anything that can’t be wetted. For example certain Filters commonly can’t be autoclaved and are instead sterilised through another approach.
Autoclaves are great at sterilising, with only a few known strains capable of surviving this approach, as with all sterile operations, it is a risk based approach to what is feasible contaminants. The few known Extremophiles are only known to exist in deep sea thermal vents and are extremely unlikely to be transmitted aboveground never mind into a pharmaceutical environment.
Once sterilised, objects must then be removed from the autoclave to be used in a process. The processes after autoclaving can easily introduce more risk to Aseptic processing and must be appropriately mitigated. This is sometimes maintained under UDAF but commonly the first intent is to make use of autoclave pouches/bags, these bags are designed to allow for steam to penetrate during an autoclave cycle but then allow handling afterwards. For biohazard sterilisation these are also commonly used to simplify processing and allow for items that may otherwise damage the autoclave to still be used such as plastics.
Autoclave cycle validation
Unfortunately, throughout history misconfiguration of validation settings and unmaintained systems have led to widespread death an illness. Thankfully these issues were investigated, root caused and finally strict regulations put in place to ensure all manufacturers prevent these from happening again. These regulations are heavily imposed and audited with breaches being taken very seriously by bodies such as the FDA and MHRA.
Before autoclaves can be used for production of medicines they must go through rigorous validation to ensure they are fit for use. Beyond the typical Installation Qualification, Operational Qualification and Performance Qualification every load pattern must be validated stating every component loaded and their position, for example with pipework it must be loaded in a specific position with a specific orientation to ensure no pooling which would mean the Latent heat transfer wouldn’t occur on the pipe surface. It’s common to prove this performance by using Biological Indicators, Chemical Indicators and performing Thermal Mapping. The most key parameters of an autoclave sterilisation process are the pressure, temperature and duration.
A key part of ensuring an autoclave is functioning appropriately is the review of data from the system, control systems are implemented to review the pressures, temperatures and times of these cycles. Regulations go one step beyond that and require two independent systems to monitor this data to prove that one system isn’t incorrectly recording, only when both of these systems say a cycle has met the requirements can the contents be approved for release.
To ensure an autoclave is working it is key to maintain and continuously check the machine is performing as expected some common checks include:
- Bowie-Dick test
- Chemical Indicator tests
- Visual Inspection
- Biological Indicator testing
- Thermal Mapping
- Leak Test
- Calibration
- Performance Qualification
Autoclave operation
Unit Procedures
There are three main types of autoclave cycles, each varying the individual Operations performed:
- Gravity Cycle - Makes use of Gravity air removal
- Vacuum Cycle - Uses vacuum air removal operation to remove air from porous/complex loads
- Liquid Cycle - Reduces exhaust rate to prevent liquid boiling and container rupture
Operations
Gravity Air Removal
In a Gravity air removal operation, air is removed from the autoclave chamber by pressurising the system with steam, as air is denser than the steam it is forced to the bottom of the chamber where an open drain allows it to escape. This process works well for systems where air can easily escape from the chamber, but can struggle to remove air from systems with porus loads or trap points for air (partially vented containers).
Vacuum Air Removal
In a Vaccum air removal operation a vacuum pump is used to pull air out of the system before being filled with steam. With loads such as porus loads/autoclave bags, air can still remain inside these despite being heavily reduced, as such Vacuum air removal operations go through a series of pulses to expand and deflate these porus loads dislodging any trapped air before continuing with sterilisation. Autoclaves are also typically fitted with sensors to detect how much air is still inside the system.
Sterilisation
Once air is removed from the system, Sterilisation can begin where Saturated Steam is used to fill the chamber. Saturated steam is used as when steam condenses the Latent heat is released at the point of condensation which releases a large amount of surface energy capable of decimating contaminants. Sterilisation cycles are typically controlled through a set pressure, temperature and time but for very high thermal load systems a F0 Value calculation is sometimes used to include the heating time in the sterilisation calculation.
Liquid Load Vent
When working with liquid loads such as broth or terminally sterilised product autoclaves can instantly boil liquids by dropping the internal pressure quickly as well as putting large strain on the containers holding them. As such for liquid cycles, when the sterilisation is completed the drain vent is controlled in opening to slowly remove this pressure, this is commonly using in conjunction with jacketed cooling to bring the product below its atmospheric boiling point before full decompression.
Passive Cooling/Drying
At the end of a sterilisation cycle, the load will be up to temperature and wet from the steam condensation. In this state the contents can’t be handled and must be cooled/dried before being removed. The simplest method of this is to simply allow the load time to cool down and for condensation to collect in the drain.
Vacuum Cooling
At the end of a cycle a vacuum can be pulled over the load allowing for faster cooling and drying. This vacuum pulls the remaining steam out of the system, reduces the boiling point for water allowing it to condense in turn drying and cooling as well as pulling any condensation out of the system.
Jacketed Cooling/Drying
For autoclaves fitted with jackets, cooling can be applied to speed up cooling of contents. This is especially useful for high thermal mass loads. This is typically completed through circulation of Chilled Water through a jacket or cooling coils.
Conclusion
In conclusion, an Autoclave is an essential tool in maintaining sterile environments across healthcare, laboratory, and pharmaceutical manufacturing settings. Its ability to harness the power of Saturated Steam for Moist heat sterilisation makes it extremely effective at eliminating a wide spectrum of microbial life.
While robust in capability, autoclaves require precise configuration, ongoing validation and regular monitoring to ensure their continued effectiveness and safety. From rigorous cycle validation to the use of dual monitoring control systems, strict adherence to regulatory standards is vital to preventing contamination and safeguarding product integrity.