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HMC sterilisation - From theory...
Procedure
The sterilization process has remained essentially unchanged since the times of Louis Pasteur and Robert Koch. Basically, sterilization is effected in a pressure vessel in an atmosphere of saturated steam in the absence of residual air. Depending on the items to be sterilized and the microorganisms to be eliminated, the sterilizing temperature will be either 121° C (1.1 bar overpressure) or 134° C (2.2 bar overpressure). To obtain a safe pressure/temperature correlation, all residual air has to be meticulously removed (vented).
Since sterilizing conditions do not yet prevail in the sterilization chamber during the venting phase (because the sterilizing temperature has not been attained and the holding time has been far too short at that point), a contaminated steam/air mixture is emitted by the steam sterilizer during venting. For this purpose an exhaust-air filtration is recommended.
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 Louis Pasteur
(1822 - 1895)
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 Robert Koch
(1843 - 1910)
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Why steam sterilization?
The high heat storage capacity of water, the additional heat released during the condensation of steam and the moisture contained in the steam form the basis of the excellent microbiological effect of steam.
By contrast with chemical sterilization or sterilization with hot air, both of which are suitable only for heat-resistant materials such as glass or metal instruments, steam sterilization is the generally accepted sterilization mode in the microbiological laboratory. From sample preparation to destruction sterilization, steam sterilizers (or autoclaves) can be used in an environmentally friendly manner.
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Sterilization is a function of temperature and time
Only sufficient holding times can assure sterilization success. In microbiological laboratories, the sterilization time is usually 15 to 20 minutes. It should be noted that liquids and culture media take much longer to reach the required sterilization temperature due to delayed heat conduction.
The sterilization time must be calculated from the point in time at which the core of the items to be sterilized has reached the required sterilization temperature. At the end of the holding time, the materials in the chamber will be sterile. Glass or instruments can be quickly taken out once the steam has been removed and the pressure has been released. Liquids should be cooled quickly to minimize liquid loss. The laboratory staff must never be endangered by delayed boiling (causing the liquid to overboil explosively).
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... to maintenance
Selection criteria
- What legal provisions must be complied with?
Genetic engineering laws, laws concerning the prevention of epidemics...
- Must other provisions be met? GLP, GMP...
- Space requirements, minimum sterilization chamber volume
- Uses: Sample preparation, waste sterilization
- Sterilization of high infectious materials, documentation
- Calibration, validation, qualifications - what requirements must be fulfilled?
- Constructive requirements, electricity, demineralized water, disposal...
- Operating and secondary costs
- Customer service
- Safety, quality and price
Quality has its price ...
... but it doesn't have to be expensive!
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Steam sterilizers
