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Steam and air sterilization process for prefilled syringe

Although the air is generally supposed to a potential problem that reduces the efficiency of steam sterilization process, yet sometimes the air’s presence is required. The liquid loads of injection drugs are often terminally sterilized in autoclaves. In this case the major function of the condensing steam is to provide rapid heat transfer to the wall of the product container, and which may be either rigid or flexible wall. All most all containers there is air, nitrogen as well as other inert gases in the upward side above the liquid. Because the solution is heated, this gas expands and adds to the pressure increase resulting from the evolution of water vapor within the container. Thus, the pressure within the steam and air sterilizer container will exceed the chamber pressure.
The glass vials can be sealed with special closures to withstand this pressure. As long as the pressure differential dose not become too great during the steam exhaust portion of the cycle, the vials will not break or burst. In those cases where rapid cooling of the loads is desired. The pressure differential might become very significant, and enough to cause container breakage or damage the closure integrity.

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The prefilled syringes, plastic bags and semi-rigid containers all present a greater problem. Because they all do not have the inherent strength like glass, as the pressure differential increases, they have a tendency to burst or open. To prevent this case from happening, the air must be injected into the steam and air autoclave chamber to raise the pressure to user defined levels. For example, to prevent the movement of a syringe plunger. This is particularly critical during the cooling cycle. When the autoclave chamber pressure is reduced at a rate greater than that within the container. This is usually referred to as air over-pressure.
The presence of air, although necessary, does reduce the efficiency of heat transfer. Therefore, when an air over-pressure cycle is used, it is necessary to maintain a well-mixed autoclave chamber environment to assure that the heat transfer to the load items will be uniform. Mixing can be accomplished by several ways. There are two major methods, that are steam air mixture process and super-heated water process. The steam-air mixture process means that a sterilization process typically used for liquid loads in which the heating medium used to heat the load item is in a mixture of air and steam. This addition of air results in an air over-pressure condition. Super-heated water means that water in a liquid phase at a temperature above 1000C requiring over-pressure to maintain this state. And the super-heated water process means that a sterilization process in which the heating medium is super-heated water that is continuously circulated with air over-pressure. This process requires air over-pressure to keep the water in a liquid states.

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