Hot Air Oven is commonly used for dry heat sterilization. Dry heat sterilization is a method of controlling microorganisms. It employs higher temperatures in the range of 160-180°C and requires exposures time up to 2 hour, depending upon the temperature employed.
The benefit of dry heat includes good penetrability and non-corrosive nature which makes it applicable for sterilizing glasswares and metal surgical instruments. It is also used for sterilizing non-aqueous thermostable liquids and thermostable powders.
Dry heat destroys bacterial endotoxins (or pyrogens) which are difficult to eliminate by other means and this property makes it applicable for sterilizing glass bottles which are to be filled aseptically). Dry heat kills by Oxidation, Protein Denaturation and toxic effects of eleveated levels of electrolytes.
Hot Air Oven, which is usually used for the dry heat sterilization is consists of the following parts:
- An insulated chamber surrounded by an outer case containing electric heaters.
- A fan
- Shelves
- Thermocouples
- Temperature sensor
- Door locking controls
How to operate a Hot Air Oven?
- Articles to be sterilized are first wrapped or enclosed in containers of cardboard, paper or aluminum.
- Then, the materials are arranged to ensure uninterrupted air flow.
- Oven may be pre-heated for materials with poor heat conductivity.
- The temperature is allowed to fall to 40°C, prior to removal of sterilized material.
Advantages
- This treatment kills the bacterial endotoxin, not all treatments can do this.
- Protective of sharps or instruments with a cutting edge (fewer problems with dulling of cutting edges).
- Dry heat sterilization by Hot Air Oven does not leave any chemical residue.
- Eliminates “wet pack” problems in humid climates.
Disadvantages
- Plastic and rubber items cannot be dry-heat sterilized because temperatures used (160–170°C) are too high for these materials.
- Dry heat penetrates materials slowly and unevenly.
- And the Oven requires a continuous source of electricity.
Safety Guidelines
- Before placing in Hot Air Oven
i) Dry glasswares completely
ii) Plug test tubes with cotton wools
iii)Wrap glasswares in kraft papers. Do not overload the oven. Overloading alters heat convection and increases the time required to sterilize.
- Allow free circulation of air between the materials.
- The material used for wrapping instruments and other items must be porous enough to let steam through but tightly woven enough to protect against dust particles and microorganisms.