Dry heat
the procedure for operation of Hot Air Oven. Procedure: 1. Connect the power supply. 2. Switch “ON” the main power supply and instrument mains. Temperature setting 3. Press SET POINT (x/w) key to set the required temperature. press ↑ to increase the temperature and ↓ to reduce the temperature 4. The temp. Sensor will maintain the set temp which is indicated by the blinking of set temp on the display screen. 5. The duration of time can also be adjusted using the time adjustment knob 6. After use,SWITCH OFF the power supply. Cleaning: Wipe the surface, walls, top, bottom and trays of the oven with dry lint free cloth on daily basis so that there will be no dust particles in the oven. Wipe all the parts and outer surface of the Oven with wet lint free cloth soaked in purified water, on weekly basis and fill the weekly cleaning record.
When sterilizing glassware such as bottles, petri dishes and test tubes, dry heat is required and this is carried out in a hot air oven. The ideal temperature of the oven needs to reach is at least 160°C and the contents need to be regulated at this heat for 45 to 60 minutes.
The Hot-Air Oven:
Mode of Action:
The effect of dry heat on microorganisms is equivalent to that of baking. The heat changes microbial proteins by oxidation reactions and creates an arid internal environment.
Procedure:
Items to be sterilized by this procedure are placed in an oven. Generally, a temperature of about 170oC maintained for nearly 2 hours ensures sterilization. The longer period and higher temperature (relative to moist heat) are required because the heat in water is more readily transferred to a cool body than is the heat in air. For example, imagine the different effects of immersing your hand in boiling water at 100oC (212oF) and of holding it in a hot air oven at the same temperature for the same amount of time.
Disadvantages:
The hot-air oven utilizes radiating dry heat for sterilization. This type of energy does not penetrate materials easily, and therefore, long period of exposure to high temperatures are necessary. For example, at a temperature of 160oC, a period of 2 hours is required for the destruction of bacterial sores. Higher temperatures are not recommended because the wrapping paper used for equipment tends to char at 180oC.
Uses of Hot Air Ovens:
The hot-air method is useful for sterilizing dry powders and water-free oily substances, as well as for many types of glassware, such as pipettes, flasks, and syringes. Dry heat does not corrode sharp instruments as steam often does, nor does it erode the ground glass surfaces of nondisposable syringes.
Important Factors to Determine the Exposure Time:
Thereby burning microorganisms removed from the materials, because organic matter insulates against dry heat. Moreover, the time required for heat to reach sterilizing temperatures varies according to the material. This factor must be considered in determining the total exposure time.
Moist Heat Sterilization. Water at high pressure level is used in moist heat sterilization. Autoclave is the instrument in which this process is carried out. ... These were the main difference between the dry and the moist heat sterilizationmethods.Nov 19, 2012
Dry heat sterilization of an article is one of the earliest forms of sterilizationpracticed. Dry heat, as the name indicates, utilizes hot air that is either free from water vapor, or has very little of it, and where this moisture plays a minimal or no role in the process of sterilization.
Hot air ovens are electrical devices which use dry heat to sterilize. They were originally developed by Pasteur. Generally, they can be operated from 50 to 300 °C, using a thermostat to control the temperature.