26 ANALYTICAL AND LABORATORY EQUIPMENT
ASSESSING EFFICIENCIES in autoclave usage
Tony Collins explains why effective autoclave loading is the key to effective sterilisation
M
uch has been written about why research institutions and
industrial laboratories use autoclaves, the whole purpose being that of sterilisation. Te aim is to destroy any microorganisms; improperly autoclaved items can result in contamination, lost time, wasted money and – in extreme circumstances – much worse. In steam sterilising the sterilising agent is, by definition, saturated steam. If the items in the autoclave do not come into contact with saturated steam then they will not be sterilised properly. Terefore effective loading of the autoclave chamber to aid steam flow and penetration and air removal is essential. Research grade and
laboratory autoclaves in the main are available with cylindrical, rectangular or square chambers. When making a purchase, chamber size has a major influence on selection. Where higher daily
throughputs are required many may opt for a rectangular chamber, as straight sides mean that more items can be loaded into the sterilising chamber, from wall to wall, top to bottom. But, when fully loaded, is the rectangular chamber design more efficient? Does it provide effective sterilisation? What about overall cost of ownership?
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Could a cylindrical chamber be a more viable alternative?
The sterilising environment To ensure that sterilisation takes place, the autoclave chamber (a sealed pressure vessel) must contain dry saturated steam held at temperatures, typically, up to 140°C and a pressure of 2.4bar, and this steam must come into contact with the items being sterilised. To create this environment, air must be removed from both the load and the chamber. Tis can be accomplished in a number of ways. Air removal from high mass, low surface area items (i.e. comprising mainly solid areas that contain little or no air pockets, such as bottled media)
will require little air removal, and can be facilitated by automatic air purging. Here, air is allowed to leave the chamber through a vent as steam enters the chamber either from an integral source (upward displacement) or an external supply (downward displacement) with the vent only closing when all of the air is removed from the chamber. Tis method can be further
advanced by ‘freesteaming’ when the vent is allowed to stay open for a set length of time once the autoclave is above 100°C. Te turbulent steam then passes through the vent, forcing any trapped air out of the autoclave. Tis helps with air removal and is useful in a different way for liquid loads as it effectively holds the autoclave chamber at
Lab autoclaves tend to be available with cylindrical, rectangular or square chambers, and chamber size has a major influence on selection
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