Sterilization is the destruction or removal of all viable micro-organisms including bacteria, viruses, fungi and spores from an object, therefore sterility is an absolute. Sterilization can be carried out using a wide variety of techniques using either physical methods such as dry heat, moist heat and radiation, or chemical methods using a variety of chemicals in liquid or vapor states.
STERILIZATION TECHNIQUES.
PHYSICAL TECHNIQUES.
Dry Heat.
Dry Heat sterilization is simply the killing of all viable organisms by the application of heat for an appropriate temperature and time period combination. Typically dry heat sterilization involves temperatures from 140 - 170 oC and exposure times of 60 -180 minutes . Sterilization can be achieved using lower temperatures with much longer exposure times.
Dry Heat has the advantages of simplicity, high penetration and lack of toxic residues. Limitations are the long time and the high temperature required, which makes it unusable for some applications.
Moist Heat.
In this technique moist heat is applied using pressurized steam as heat is transferred much more rapidly from steam than air. The process usually is carried out in a pressure vessel due to operating requirements, from which air is removed so that steam can be saturated. In Steam sterilization typical operating conditions are Temperatures between 121-132 oC, pressures from 100 - 130 kPa (gauge) and Exposure times 5 - 45 minutes .
Advantages of steam distillation are similar to those of dry heat sterilization with the additions faster processing times and lower operating temperature requirements. Limitations are that it can't be used to sterilize materials which are moisture sensitive or sensitive to required temperatures. .
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Radiation.
In Radiation Sterilization sufficient radiation is applied to destroy all viable micro-organisms. Radiation kills cells by ionization, mutation, cell wall disruption and other means.
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