Hot Air Oven Parts and Functions

A procedure of decontamination known as “hot air oven sterilisation” involves an electrical apparatus that uses dry heat to sterilise various types of equipment or items housed inside its chamber. It is used to sterilise items that cannot be sterilised using water and items that are more susceptible to dry heat. Louis Pasteur was the one who invented it first.

Hot Air Oven Definition

A hot air oven is a scientific equipment that employs dry heat to disinfect equipment and other objects. Hot air ovens are also referred to as forced air circulating ovens.

Dry heat sterilisation is a technique used to disinfect items that cannot be soaked in water or materials that won’t melt, catch fire, or alter shape when subjected to high temperatures.

To sterilise the various objects, equipment, and so on, it uses a heat conduction mechanism. Their holding temperature ranges between 150 and 180 degrees Celsius. Their holding time ranges between 20 and 150 minutes.

Because of their simple standard operating procedure and low cost, most clinical sectors use hot air ovens to sterilise laboratory instruments and materials. It also allows for quick drying processes.

It uses higher temperatures in centigrade and requires up to 2 hours of exposure time, depending on the temperature.

The dry heat sterilisation technique necessitates a longer exposure time (1.5 to 3 hours) and a higher temperature than the moist heat sterilisation technique.

Hot Air Oven Principle

Hot air ovens work on the principle of killing microorganisms with dry heat at temperatures ranging from 140 degrees Celsius to 260 degrees Celsius for an extended period of time. This method can kill all microorganisms, including bacteria and spores.

Vegetative microbes are killed in 180 minutes, 180 degrees Celsius, and 45 minutes. This destruction occurs at 260 degrees Celsius due to the oxidation of essential cell constituents.

Construction of Hot Air Oven

Dry Sterilisation Process

This method was originally used in a hot-air oven. Sterilization oven is suitable for glassware, powders and oil-containing materials. The hot air oven works in such a way that the items inside it don’t catch fire or meltdown. It works on the principle that heat travels from the outside to the inside of the material and the item’s core. Because the hot air is used to sterilize the item, it is called a dry sterilization procedure.

The air becomes hotter and thins as it moves towards the ceiling. When air touches the roof, it travels towards ground. This helps to circulate air in the chamber. The chamber is heated evenly by the current flow. Hot air sterilizer is a more complicated method than moist sterilization or autoclaving. It is necessary to have some organizational facilities if sterilization is done in a medical laboratory.

Parts of Hot Air Oven

Dry heat sterilization oven are made up of many parts, which can be classified into two main categories: Interior parts and exterior parts.

diagram of hot air oven

Diagram of Hot Air Oven

i. Exterior parts

Main switch: The main switch is used to turn on or off the instrument. When the device is turned on, a green indicator illuminates.

Regulator: temperature regulator is used to adjust the temperature as needed (Diagram of oven:1). The temperature rises when the knob is turned to the right and falls when it is turned to the left.

Thermostat: thermostat is located at the top, with one end inside the oven. Its purpose is to monitor and maintain the desired temperature within the hot air oven.

Door jacket: This is the double-walled outer jacket made of glass-wool fibre. Its primary function is to keep the heat generated within the chamber contained, thereby conserving energy. It provides maximum thermal efficiency while also protecting the instrument surfaces from heat damage (Diagram of oven:1).

ii. Internal parts

Inner chamber: Stainless steel is used for the inner chamber, supporting long-term operation and providing corrosion resistance. There are tray slots on both sides, which the tray shelves can slide into or out of depending on the height and volume of the items to be sterilised. The stainless steel wire mesh cable used to make the tray holder.

Temp Sensors: The hot air oven’s internal temperature is measured by a temperature sensor, which then shows the result on the controller screen (Oven diagram:1).

Hot Air vents: Hot gases and excessive heat are expelled outside the oven through air vents that are situated at the top of the chamber.

Aluminium trays: On the aluminium trays of the hot air oven, items like glassware and metals are stored. The trays are typically perforated to help the items stored inside get an even distribution of heat.

Circulating fans: A crucial part of the hot air oven’s enhanced temperature dispersion and uniform heat flow is played by circulating fans (Oven diagram:1).

Heating element: The instrument’s bottom is covered with electrical coils, allowing heat to travel upward.

Types of Hot Air Oven

Hot air ovens are typically available in two configurations: static and forced air.

i. Static Air-Type Oven

The hot air can move upward in this because the electric coils are situated at the bottom. Heat is transferred by gravity convection, which uses electrical coils at the bottom. It is not very effective at transferring heat energy.

ii. Forced Air-Type Oven

The motor-driven blowers in this allow for the even distribution of heated air. Forced or mechanical convection, such as that produced by air blowers, is how heat is transferred. It transmits the energy from the dry air to the instrument more quickly because it is more effective at transferring heat.

Procedure of Hot Air Oven

When handling it, the following factors must be taken into account:

  1. Only use items that can be sterilised with dry heat. By employing a hot air oven, we may sterilise a variety of objects, including glassware, powder, materials containing oils, and metal tools.
  2. Place the items into an aluminium or cardboard container, or wrap them in paper or newspaper. Also good for wrapping are metal jars. Test tubes, flasks, and pipettes’ exposed ends can be sealed using cotton wool.
  3. Next, set up the items so that air may circulate freely. Close the door after properly positioning it, then turn the hot air oven on. The temperature will then start to increase.
  4. Check the time needed to hold the material at the desired temperature once it reaches the right temperature. To reduce the likelihood of glassware breaking, switch it off and let it cool to 60°C.
  5. The temperature of the hot air oven determines the holding period for the sterilising. 120 minutes at 160°C is considered typical.

Uses of Hot Air Oven

Hot air ovens carry out a number of tasks in several industries, including:

  1. Hot air ovens effectively reduces the moisture content in most objects, making it very perfect for baking, curing, drying, and annealing.
  2. Used to sterilise heat-stable glass objects such as flasks, pipettes, Petri dishes, and test tubes, among other things. Also employed for sterilising metal tools like scalpels, forceps, scissors, and forceps. Used to sterilise non-volatile substances such as zinc, starch powder, and sulphonamide.
  3. Hot air oven is also widely applied in operations based on study in the life sciences (labs, clinical services, manufacturing plants).
  4. In laboratories for life sciences and microbiology, it is used to sterilise N95 masks, dry glassware, clean general instruments, and package goods.
  5. It is employed to keep things at a consistent temperature in several laboratories and medical facilities. Measurement of mixed liquid suspended solids is another use for it.

Hot Air Oven Advantages

  1. It is easier to handle and safer to deal with because there is no need for water to sterilise the material and there isn’t as much pressure created as in an autoclave.
  2. It is more appropriate for use in a laboratory setting than other sterilisers. When compared to autoclaves, hot air ovens are much smaller and more efficient.
  3. When compared to other methods, a hot air oven can be faster than an autoclave and achieve higher temperatures.
  4. In comparison to other sterilisation methods, the operating procedure is straightforward.
  5. It is less expensive than an autoclave.
  6. Only the hot air oven can sterilise oils and powder. They cannot be sterilised in autoclaves because moisture can cause clumping.

Hot Air Oven Disadvantages

  1. Due to the use of dry heat rather than wet heat, it cannot slaughter some living organisms, such as prions, according to the principle of thermal inactivation by oxidation.
  2. Most materials, such as surgical dressings, rubber items, or plastic material, are incompatible with hot air ovens and can melt at low temperatures.

Conclusion

As a result, we can draw the conclusion that the hot air oven works as an enclosed space that restricts the heat produced by the electrical current to dry and sterilise the specimen stored inside. It uses dry heat to eliminate moisture from the apparatus and sterilise heat-resistant materials by eradicating microorganisms or microorganism spores.

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