The Choice is Yours

27 October 2011

Advances in sterilization technology and knowledge over the last ten years have been huge, and customers are now demanding more functions and features on their autoclaves to ensure that their loads are sterilized quickly and effectively.

The range of autoclaves, options and accessories has never been greater, which means that pitfalls can exist when choosing the right autoclave for your application. On one hand, over-specifying the autoclave wastes money, whilst on the other, under-specifying can leave you with an autoclave which does not fulfil its operational requirements.

Careful consideration to the many features available on today’s autoclaves will ensure that you get the right product for the right job and below we attempt to unravel just some of the issues you may need to consider.

How will Steam be Generated? This is an area which can cause some confusion. There are three main methods of generating steam (2 x electric and 1 x direct steam). The first electrical method is by using heating elements inside the chamber. Water is poured into a reservoir to the correct level and away you go.

This is the lowest cost option both in terms of capital outlay and installation costs. However there are potential drawbacks. For example, loads will always be wet at the end of the cycle, and breakages/spillages need to be cleared away as soon as possible, which can be messy and time-consuming (leaving the spillage can lead to that familiar smell we all know and love!!!).

This can be improved by fitting auto-drain and auto-fill options. The other electrically heated method is to fit a separate steam generator, which on most lab autoclaves is fitted underneath the chamber, within the frame. This is a more expensive option but has the advantage of giving a unencumbered and cleaner work space and dryer loads at the end of the cycle. It can also speed up the cycle times considerably.

If you have your own direct steam supply then you have the best of both worlds. The capital costs will be lower, running costs will be lower and the cycles times will be shorter.

Cycle Recording. Most laboratories require some form of cycle record and historical data for internal traceability and audit trails. The options available here are many. The most popular is to fit a data printer, which should be capable of printing load and chamber temperatures, load pressures, cycle data and cycle status (pass/fail), in line with GLP requirements.

Some autoclaves can now incorporate internal or remote data archiving systems which will store data onto an internal flashcard or download direct to a PC. Chart recorders are still a tried and trusted method for recording cycle data. These now come in a multitude of guises including multi-pen recorders and also graphic types, which again can be downloaded to a PC.

Measuring Load Temperatures. It is becoming more important to be able to track the temperature of the load, so most manufacturers will either include a load probe as standard or offer one as an option. The load probe ensures that the load receives the correct exposure time at the sterilizing temperature and should also prevents the door from opening until the load has reached a safe temperature (normally 80ºC or below).

Vacuum Systems. This is the area that requires possibly the most consideration. Most manufacturers will offer a vacuum pump of some description on some or all of its ranges, but is it right for your application or needs? In essence there are two types of vacuum pump available. The first is a diaphragm vacuum pump. These are relatively inexpensive, but do have limited performance.

Typically, vacuum levels will reach 500-600mbarA which means their use is limited to providing improved air removal at the beginning of the cycle, plus it will help to dissipate heat in some load types at the end of the cycle. If that’s all you need it for, then this is ideal.

However, for more effective air removal (important when sterilizing bagged goods or hollow-ware, such as pipette tips, tubing etc), then choosing an autoclave with a liquid ring vacuum pump may be more appropriate. These pumps will achieve a much higher vacuum (typically 30-100mbarA), which offers enhanced air removal, but, more importantly will flash off much of the residual water from deep inside the load during the cooling stage, which can be very important with hollow-ware loads.

Drying. More customers are requiring that certain loads are totally dry at the end of the cycle. Typical loads can be pipette tips, tubing, instruments and porous loads such as lab gowns and shoes. Vacuum alone (even using liquid ring pumps) will not achieve totally dry loads. The only way to dry loads effectively is by adding a steam jacket to the chamber. The heating effect of the steam jacket plus the high vacuum flashes off all residual moisture from the load, whilst minimising cycle times.

Air Ballast. The longest cycle for a lab autoclave is usually the media cycle. The cooling stage usually needs to be slow in order to prevent bottles/containers from breaking, or to prevent media volume loss due to boiling-over. If the cooling is too fast, the chamber reaches atmospheric pressure too quickly which can cause the breakages or volume loss.

An increasingly popular method of speeding up cycle times and reducing the risk of breakage and volume loss is to specify an air ballast system. This system basically introduces an over-pressure into the chamber during cooling using compressed air. With sealed media, this equilibrates the pressure between the chamber and the inside of the sealed bottle/container, thus preventing the breakage. With unsealed media, the over-pressure helps to keep the media inside the bottle/container.

Environmental Issues. This is an area of increasing importance to customers, yet it is widely misunderstood. Various methods can be incorporated into autoclaves to improve the usage of such services as electricity and water.

Whilst using fans is an accepted method of cooling autoclave chambers and is offered by most manufacturers, it is quite a slow cooling method (which means it uses more electricity). Many autoclave manufacturers also offer ranges that use water coils or jackets as a cooling method. These methods obviously use more water than fan cooled autoclaves (although cycle times tend to be much lower, so electricity costs should be less), however you should ensure that these systems are as environmentally friendly as possible. All water should be re-circulated via an integral hold tank. This type of system normally only replaces water once it has reached a pre-set temperature, which can significantly reduce the water usage.

Power consumption is also an issue for many. Most power is consumed during the heat up stage. Selecting an autoclave with the most efficient heating up method will save a considerable amount of money over the life of the autoclave.

The autoclave with the lowest power consumption would be that which uses a site steam supply as no heating is involved here.
Next would be those with separate steam generators kept on constant standby, due to the fact that once the generator has reached temperature, it simply ‘ticks over’, using relatively little electricity.

Next are autoclaves with either a separate steam generator or internal heaters.

The autoclave most likely to consume the most power would be those which have internal heaters and an auto-drain facility, because this means that the water is drained and replaced after every cycle, making it necessary to heat up the water from cold every cycle.

Hopefully this guide offers you an insight into the increasingly complex area of specifying your next autoclave and highlights some of the areas which will need careful consideration.

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The Choice is Yours

27 October 2011

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