Hot Air Oven: Definition & Working Principle

Hot Air Oven: Definition & Working Principle

hot air oven

A hot air oven may be a variety of dry heat sterilization. Dry heat sterilization is employed on instrumentality that can’t be wet, and on material that may not soften, catch fire, or deform once exposed to high temperatures. wet heat sterilization uses water to boil things or steam them to sterilize and doesn’t take as long as dry heat sterilization. Samples of things that aren’t sterilized in an exceedingly hot air oven are surgical dressings, rubber things, or plastic material. things that are sterilized in an exceedingly hot air oven include:

Glassware (petri dishes, flasks, pipettes, and test tubes)

Powders (starch, zinc oxide, and sulfadiazine)

Materials that contain oils

Metal instrumentality (scalpels, scissors, and blades)

Hot air ovens use very high temperatures over many hours to destroy microorganisms and microorganism spores. The ovens use physical phenomenon to sterilize things by heating the surface surfaces of the item, that then absorbs the warmth and moves it towards the middle of the item.

The commonly-used temperatures and time that hot air ovens ought to sterilize materials is 170 degrees celsius for half-hour, 160 degrees celsius for hr, and 150 degrees celsius for 150 minutes.

An oven provides a temperature more than that of atmosphere.

• The temperature vary by ovens is between 50-250°C.

• These are used for speedy evaporation of materials, speedy drying and for sterilization of articles which will be sterilized by dry heat.

• Dry heat sterilization technique needs longer exposure time (1.5 to three hours) and better temperatures than wetter sterilization.

Hot Air Oven: Principle, Types Precautions and Application


Sterilizing by dry heat is accomplished by physical phenomenon. the warmth is absorbed by the surface of the item, then passes towards the Centre of the item, layer by layer. The whole item can eventually reach the temperature needed for sterilization to require place.

Dry heat will most of the harm by oxidizing molecules. The essential cell constituents area unit destroyed and also the organism dies. The temperature is maintained for nearly an hour to kill the foremost troublesome of the resistant spores.


There are 2 varieties of hot air ovens.

One may be a forced air hot air oven and also the alternative may be a static air hot air oven. The forced air hot air oven is more practical than the static air hot air oven.

1. The forced air hot air oven

It works by heating the oven and employing a fan to maneuver the recent air around. This helps forestall the recent air from rising to the highest of the oven and keeping the cooler air at the bottom. The fan keeps the recent air on the move at an even temperature throughout the oven.

2. The static air hot air oven

It works by employing a heating coil at very cheap of the oven. the warmth rises throughout the oven and takes a extended time to achieve the specified temperature. Since the warmth isn’t circulated like a forced air hot air oven the temperature isn’t consistent throughout the oven.


The foremost common time-temperature relationships for sterilization with hot air sterilizers are

170ᵒC (340ᵒF) for half-hour,
160ᵒC (320ᵒF) for hour, and
150ᵒC (300ᵒF) for 150 minutes or longer relying up the amount.
The contents should not be faraway from the hot air oven instantly as a slow cooling amount is important – ideally once the temperature has reduced right down to 50°c, however no less.

The explanation for the gradual cooling amount is to avoid the cracking of glasswork moreover as preventing air (that may probably contain contaminating organisms) coming into the kitchen appliance.

Used for glasswork, forceps, swabs, water tight oils, waxes & powders

Hot Air Oven: Principle, Types Precautions and Application

Precautions to be taken.

Dry glass work utterly

Plug take a look at tubes with cotton

Wrap glass work in kraft paperpapers

Don’t over load the hot air oven

Enable free circulation of air between the fabric.

Quality control

to visualize whether or not the instrumentation is functioning properly one.

Chemical controls: Browne’s tubes Color modification from red to green

2. Biological controls: paper strips containing 10⁶spores of C. tetani

Place strips in hot air oven at the side of different material for the sterilization

Later culture the strips in thioglycollate broth at 37 ᵒC for five days

Growth in medium indicates failure of sterilization


• A dry heat cupboard is straightforward to put in and has comparatively low in operation prices

• It penetrates materials

• it’s nontoxic and doesn’t damage the surroundings

• it’s noncorrosive for metal and sharp instruments.


• Time intense technique thanks to slow rate of warmth penetration and microbic killing.

• High temperatures don’t seem to be appropriate for many materials.


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