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Dear Lynda
A steam sterilizer, also known as "autoclave," is a pressure-type vessel with one or two door, valves to control the entry and exit of steam and air, and monitoring devices to allow the operator to observe conditions inside. It is designed to allow steam under pressure to penetrate the loaded items.
Moist heat (saturated steam) under pressure and raised temperature damages the cells essential structures including the cytoplasmic membrane rendering the cell no longer viable. The critical factor in the destruction of microorganisms is the relationship between temperature, pressure and time of exposure. The most common type of steam sterilizers used in CSSD's in Europe are Prevacuum Autoclaves.
The prevacuum - sterilization process includes:
- Pre-vacuum phase:
Air removal by a vacuum pump that draws the air out while simultaneously injecting steam into the chamber. As more steam enters the chamber, the pressure increases and steam and air form a mixture. When a pre-determined pressure is reached, the drain opens and the pressurized steam an air rush from the chamber creating a vacuum. The injection and vacuum process is repeated four times in series to evacuate all air from the chamber.
- Raising time:
Once the air is removed from the load and chamber, steam is injected into the chamber until the thermal sensor probe placed in the chamber drain line reaches the pre-selected temperature.
- Exposure time (Plateau time):
When the thermal sensor registers the set temperature the steam injection valve will close, the timing mechanism will be activated and the exposure time, the actual sterilization time, will begin. When the sensor register a drop of the temperature, the steam valve opens and steam will be injected to reach the preset time again. Pre-vacuum sterilization parameters for porous load are between 132-135°C (279-272°F) for 3 to 4 minutes with a pressure of about 45 psi.
- Exhausting time (post-vacuum):
When the exposure time is completed the steam will be removed by the vacuum pump.
- Drying time:
When the post-vacuum time is completed sterile filtered air is injected into the chamber to relieve the vacuum. The cycle is complete.
Under the category "Steam sterilization" on the Q/A page you will find answers to the differences between Prevac- vs. Gravity Sterilization. And of course for in-depth information see our Book Recommendations on the Education page.
I hope this brief explanation is of some help to you.
Kind regards
Josy Holdener
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