Dry heat sterilization is a process of killing or removing of all microorganisms, as well as bacterial spores. Technique needs longer exposure time two to three hours and higher heat than steam heat sterilization. There are several obtainable techniques of dry heat sterilization which are incineration, flaming, and hot air oven etc. sterilization of wire loop. Dry heats ovens are widely-used to sterilize materials which might be damaged by dry heat or that are impenetrable to dry heat e.g. petroleum products, sharp instruments, and powders.
Principle of Dry Heat Sterilization Using HOT AIR OVEN
Disinfecting by dry heat is achieved by conduction. The heat is soaked up by the outside surface of the material, and then moves towards the centre of the material, layer by layer. The whole material will ultimately reach the temperature needed for sterilization to occur.
Dry heat does most of the damage by oxidizing molecules. The crucial cell constituents are killed and the organism dies. The temperature is retained for almost 60 minutes to kill the toughest of the absorbent spores. The most popular time-temperature relationships for sterilization with hot air sterilizers are 1700C for half hour, 1600C for an hour, and 1500C for two hours thirty minutes or longer it dependson the volume of temperature.
Atrophaeus spores must be used to monitor the sterilization process for dry heat since they are more defiant to dry heat than the spores of Geobacillus stearothermophilus. The main toxic process is considered to be oxidation of cell components.
There are two types of dry-heat sterilizers:
- The static-air type and
- The forced-air type
The static-air type is known as the oven-type disinfectant as heating coils in the underneath of the unit cause the hot air to go up inside the chamber through gravity convection. This kind of dry-heat sterilizer is far slower in heating, needs longer time to attain sterilizing temperature, and is less standardized in temperature control throughout the chamber than is the forced-air type.
The forced-air or mechanical convection sterilizer has a motor-driven blower that circulates heated air all over the chamber at a high pace, enabling a more quick transfer of energy from the air to the equipments.
Dry heat sterilization is particularly appropriate to materials that are destroyed by high pressure or moisture and can tolerate high temperatures. Dry heat does not cause destruction of metal equipments; hence it is suitable for the sterilization of metal equipments but cannot be employed for sterilization of fabrics, plastics or rubber-ware. Additionally it is recommended for glassware in the laboratory. The final division is materials that steam cannot absorb or should remain dry: This includes pharmaceutical powders that must remain dry, oils and substances that are not penetrated by steam.
Some Advantages of Dry Heat Sterilization
- It penetrates materials
- Dry heat cabinet is simple to install and possess low operating costs;
- Suitable for sterilizing materials and instruments that cannot be autoclaved
- And it is un-caustic for metal and thorny instruments.
- It is nontoxic and does not harm the environment;
- Usually cheaper than an autoclave