Saturated steam in autoclave


Steam or heating methods are the most widely used and reliable sterilization techniques. The main principle of this method, as achieved in autoclave installations, is to allow each object to be in contact with steam at the required amount of heat for a specific time. So why is steam so effective?

How is saturated steam produced in a autoclave?

We open the door and put the load inside the autoclave. Load refers to anything we wish to disinfect, namely surgical instruments, as well as laboratory necessities such as solid, liquid or hollow. Once we close the door and set the Steam autoclave to the proper cycle, the water begins to enter the Autoclave chamber and is heated to 121 ° C or 134 ° C to generate steam. Steam can be generated indoors or externally by steam generators.

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In an autoclave, all air is removed, leaving only steam. This pure steam is called saturated steam. “Saturation” means that the steam occupies a space that cannot accommodate any more steam and is completely filled with a high concentration of ultra-concentrated steam. The optimum composition of steam in an autoclave is 3% liquid and 97% gas. Any change in moisture percentage will increase or decrease sterilization time.

When steam touches the surface of a cooler object, such as a load in an autoclave, heat is transferred from the steam to the cooler object, thus heating it. This is called the heat of condensation. The saturated steam used for sterilization reaches a high temperature of 121℃ or 134℃, so high that when it comes into contact with the load and condenses, the heat transfer is sufficient to kill all microorganisms on the load. This is one of the reasons why steam is such an effective fungicide.


As we have just explained, saturated steam has a great ability to transfer heat to cooler loads, allowing steam to penetrate deep into the interior of the load. In addition, when the steam condenses on the sterilized load, the volume of the steam shrinks (gathers and becomes smaller) until it becomes moist on the surface of the load. As a result, there is more room for steam. The pressure then condenses the steam, and more steam is then drawn into the autoclave chamber. This whole process causes the temperature and pressure of the room to increase.


Another reason saturated steam is the preferred disinfectant is that it contains the most humidity. The presence of humidity is critical to the steam’s ability to kill microorganisms. Wet heat is more destructive than dry heat. Think of a wound caused by boiling water or steam versus a wound caused by something that came into contact with heat. Wounds caused by wet heat are more painful and deeper than those caused by dry heat. Similarly, the wet heat of steam can attack microbes more deeply and efficiently than dry heat, because steam transmits heat better than hot air.

In addition, many microbes contain water, and those that do are more likely to be killed by damp heat because the water inside them is combined with the powerful moisture-heat transfer effects of steam. Even for microorganisms that have no water (such as dried spores) or very little water, steam remains the fungicide of choice.

As we explained above, wounds caused by boiling water or steam can be more painful and deeper than those caused by dry heat alone. The steam itself hydrates the spores and makes up for the lack of water inside the spores. Thus, for spores that lack internal moisture, the steam causes moisture destruction.

The Steam autoclave is a fast and efficient machine that kills most types of bacteria. Assuming you want to ensure that your facility maintains a high level of cleanliness, we can help you obtain high quality equipment to ensure that your work area is safe for your employees and patients.

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