Medical autoclaves are a vital component in the fight against infection control and are in essence, a giant pressure cooker – albeit a sophisticated version of the kind you might use in your kitchen to cook meat, pulses and veggies etc.
Like a domestic pressure cooker, an autoclave uses steam but this time, to kill bacteria and micro organisms in order to sterilise tools and equipment. But how does it work?
An autoclave is a large pressurised vessel sometimes cylindrical in shape that is able to withstand high temperatures. They come in many different sizes from smaller medical desktop autoclaves – like the kind you might find in a dental clinic – right up to massive industrial versions – the largest of which is over 30 metres long and 9 metres wide.
However, despite their different appearances, the principle is mostly the same – to cleanse equipment, tools and parts from any foreign objects that may otherwise cause harm, damage, or spread disease.
Just like a kitchen pressure cooker, any equipment or tools are placed inside and the lid is sealed – The words ‘auto’ and ‘clave’ together mean automatic locking. Once everything is secured inside, next comes the important part – The removal of as much air as possible.
This is vital because, in order to achieve effective sterilization and disinfection, saturated steam needs to come into direct content with the item.
Why is this important?
Because, when excess air remains, it creates a barrier and prevents the steam from fully penetrating the equipment or tool.
A word about Autoclave types of sterilization and air removal
There are in effect two ways to remove air and a medical autoclave uses both methods. It can be done through
- Gravity displacement – a unit will remove and displace any air by pumping steam at high pressure directly into the vessel
- Pre-vacuum – This method utilises a vacuum pump to primarily remove all the air. Once all the air is removed, steam can then be pumped in.
The difference between the two autoclave types
Gravity displacement autoclaves are the most basic types of autoclave and ideal for removing matter from non-porous items – for example, those with hard surfaces. These include unwrapped steel utensils, glassware and equipment. They can be cheaper to buy as they don’t rely on peripheral mechanisms such as vacuum pumps to remove excess air.
Conversely, in instances where air cannot easily be removed from items such as towels, wrapped surgical kits, pipette tips, and high-density polyethylene products including syringes, then an autoclave with a vacuum function should allow for better air removal and therefore deeper steam penetration. Naturally, these are a bigger investment.
A word about autoclave air detectors
Although air detectors are commonly fitted to autoclaves, they are not always sufficiently sensitive enough to detect the presence of small amounts of air, particularly if that air is trapped within a load such as surgical towels or syringes. As a result, it isn’t a good idea to rely on them alone.
Establishments are better advised to carry out a more direct way to test for sufficient air removal in the guise of a test pack such as a Bowie-Dickie, Brown’s TST pack, or AMSCO Dart pack. These are simple tests which are placed into the vessel and designed to highlight the presence of excess air.
Here at Critical Dental we sell a wide variety of testing kits so feel free to check out our latest catalogue for more details
How an autoclave uses steam to sterilise instruments? The sterilisation and disinfection process
For an autoclave to work, it needs 3 elements. These are steam, pressure, and time.
Once sufficient air has been removed, the sterilising process can begin. As the steam is pumped into the chamber, pressure and heat are maintained long enough to sufficiently kill all micro organisms or bacteria to ensure complete sterilisation of many medical-grade tools.
The difference between autoclaves and dry-steam sterilizers
While an autoclave uses wet steam to sterilise medical-grade tools and equipment, a dry steam sterilizer (as the name suggests) uses dry steam to kill bacteria.
Where a wet-steam autoclave reduces humidity to around 3%, a dry-steam sterilizer reduces the area to zero humidity. This means that a sterilizer becomes in effect, a dry-heat oven. Think kitchen pressure cooker vs standard oven!
Although many loads can equally be sterilized using either dry heat sterilizers or steam autoclaves, the steam sterilization method is usually more energy-efficient and less time consuming than super-heated steam sterilizers. This is because to kill most types of bacteria a dry heat sterilizer has to reach temperatures of 170 degrees Celsius which needs to be held for 1 hour.
On the contrary, a wet steam autoclave uses lower temperatures of around 130 degrees Celsius for a fraction of that time – usually for somewhere between 3 and 20 minutes. As a result, it’s considered more economical and less time consuming than the former.
That said, dry-heat sterilizers are not ideal for flammable or dense loads so you will need to use an autoclave to achieve optimum sterilisation. Do remember however that the target time and maintained temperature will vary depending upon several factors. These include:
- Autoclave type – Dry or wet steam
- How full or empty the autoclave is – the restricted movement of steam will affect the time needed to thoroughly cleanse the equipment within.
- Tools/equipment type
All of this is something the operator will need to take into consideration.
So there you have it – everything you need to know about autoclave uses, types, and how they work.
If you are looking to upgrade your autoclave, then you might want to consider purchasing from Critical Dental. Please don’t hesitate to get in touch with our customer service team on (02) 8074 3770. As an Australian company, we have a good range of Autoclaves from the top name and trusted brands. Browse our catalogue to see some great prices today