Hot air oven Definition
- A hot air oven is a laboratory instrument that uses dry heat to sterilize laboratory equipment and other materials.
- That equipment cannot be wet or material that will not melt, catch fire, or change form when exposed to high temperatures are sterilized by using the dry heat sterilization method.
- Hot air oven also known as forced air circulating oven.
- Some examples of material which can not be sterilized by employing a hot air oven such as surgical dressings, rubber items, or plastic material.
- We can sterilize Glassware (like petri dishes, flasks, pipettes, and test tubes), Powder (like starch, zinc oxide, and sulfadiazine), Materials that contain oils, Metal equipment (like scalpels, scissors, and blades) by using hot air oven.
- To destroy microorganisms and bacterial spores, a hot air oven provides extremely high temperatures over several hours.
- The widely used temperature-time relationship in hot air ovens to destroy microorganisms are 170 degrees Celsius for 30 minutes, 160 degrees Celsius for 60 minutes, and 150 degrees Celsius for 150 minutes.
- Most of the medical industries use hot air ovens to sterilize laboratory instruments and material due to its simple standard operating procedure and low price. It also provides quick-drying processes.
- The process of dry heat sterilization using a hot air oven Originally developed by Louis Pasteur.
- The temperature range of a hot air oven is 50 to 300 ° C. It can be controlled by using a temperature regulator.
- The forced air circulation provided by the oven ensures the temperature uniformity throughout the oven.
- In a hot air oven first, the surface of the material is sterilized then the temperature slowly enters the center of the item.
Working Principle of Hot air oven/Hot air oven principle
Sterilization by dry heat is performed by conduction. The temperature is consumed by the surface of the objects, then moves towards the core of the object, coating by coating. The whole object will ultimately attain the temperature needed for sterilization to take place.
Dry heat causes most of the injury by oxidizing particles. The primary cell components are damaged and the organism dies. The temperature is kept for about an hour to eliminate the most ambitious of the resistant spores.
It is originally used in a hot air oven. This method is proper for items like glassware, powders, oil containing materials, metal material. Hot air oven acts in a manner so that items stored inside the oven don’t grab fire or meltdown. It primarily acts on the principle of structure where heat moves on the outside of the substance and then to the core of the item. It is termed a dry sterilization process because the procedure is performed by employing the hot air.
While the air shifts hot, it becomes thinner and transfers towards the ceiling of the chamber. If air hits the roof of the chamber it travels towards the ground of the chamber. It helps in the circulation of air within the chamber. This current flow assures the proper and uniform heating everywhere in the chamber. This is approaching a longer method than autoclaving or moist sterilization. Hence, a few organizational facilities are needed if it is practiced in the medical laboratory, so that workers can create a schedule of the sterilization method.
Hot air oven Parts and Functions
- External cabinet: The External cabinet is made of stainless sheets. It covers the inner chamber.
- Glass wool insulation: The space between the inner chamber and external cabinet is filled with Glass wool. It provides insulation to the hot air oven.
- Inner chamber: The inner chamber of the hot air oven is made of Stainless steel.
- Tubular air heaters: They help to generate heat within the inner chamber. Two Tubular air heaters are located on both sides of the inner chamber.
- Motor-driven blower: It helps in uniformly circulating the air within the chamber.
- Temperature sensor: It measures the temperature within the hot air oven and displays it on the controller screen.
- Tray slots: The inner wall of the chamber contains several try slots that hold the trays.
- PID temperature controller: It maintains the accurate temperature during the entire cycle. It also controls the temperature and also displays the temperature values.
- Load indicator: it indicates the hot air oven is overloaded.
- Mains on/off switch: It helps to turn on/ turn off the hot air oven.
- Safety thermostat: It is also known as an over-temperature protection device. It keeps your oven and specimen safe in case of controller malfunction.
Types of hot air oven
There are present different types of hot air oven such as;
- Gravity Convection Air is distributed by spontaneous convection. As hot air flows up, a gentle flow holds temperatures moderately uniform inside a container and wholly uniform in any distinct position.
Forced Convection Ovens
- These ovens carry a fan that gives limited air circulation within the heating container.
- This method provides very fast heat up and restoration times, mixed with especially low-temperature differences inside the working chamber.
- Flexible vents and semi-forced exhaust deliver it a conventional sample-drying oven.
- Mechanical Convection is a gravitation convection oven served with a re-circulating fan in a working container.
Forced Exhaust Ovens
- In these ovens, air is pushed into the working container by a fan and scattered through an adaptable vent.
- This variety of oven is especially helpful in purposes where the heating process provides vapors or fumes that require to be immediately and continuously discharged from the working container.
- All of the forced air ovens consume at a higher percentage than a convection oven. Though, much larger forced exhaust velocities can be accomplished by adding an air channel and a flexible outlet.
- This adjustment takes an extra $100 and is totally achievable with forced convection ovens.
Side Draught Ovens
- Certain ovens produce airflow from one side to the other i.e. left to right.
- Speedy heat up and restoration time make this type of oven prototype for preheating plastic cloths(hospitals, etc.) or any profession where smooth sheets or plates are used.
Hot air oven Pros/Advantages
- No need to water to sterilize the material.
- Not much pressure is created like autoclave which creates it easy to manage and also makes it safer to work with.
- In a laboratory environment, it is more fitting to use as compared to other sterilizers.
- Hot air oven is much smaller in size as compared to autoclaves and also more effective.
- A hot air oven can be more speedy than an autoclave and higher temperature can be achieved as compared to other means.
- The operating procedure is simple as compared to other sterilization methods.
- Its price is low as compared to autoclave.
Hot air oven cons/Disadvantages
- According to the principle of thermal inactivation by oxidation, it can not slaughter some living organisms, such as prions due to the use of dry heat rather than wet heat.
- Most of the materials are not fit with hot air ovens such as surgical dressings, rubber items, or plastic material; they can be a meltdown at low temperatures.
Hot air oven Application/Hot air oven uses
- It is used to dry glassware, sterilize N95 masks, general instruments, and packaging items in life science, microbiology laboratory.
- It is also used in chemical and pharmaceutical industries, food and beverage industries, textile industries.
- It helps in the elimination of moisture from the material thus it is used in curing, drying, baking, and annealing.
- It is also used for the Measurement of mixed liquor suspended solids (MLSS).
- In certain laboratories and hospitals, it is used to store materials at a constant temperature.
A hot air oven is a laboratory instrument that uses dry heat to sterilize laboratory equipment and other materials.
The commonly-used temperatures and time that hot air ovens need to sterilize materials is 170 degrees Celsius for 30 minutes, 160 degrees Celsius for 60 minutes, and 150 degrees Celsius for 150 minutes.
Hot air ovens use extremely high temperatures over several hours to destroy microorganisms and bacterial spores. The ovens use conduction to sterilize items by heating the outside surfaces of the item, which then absorbs the heat and moves it towards the center of the item.
Sterilization by conduction of dry heat. Heat is absorbed by the material from outer layer towards center until finally the entire item reaches the temperature of sterilization.
Hot air sterilization is one method of effectively killing microbes of all kinds, especially bacteria, viruses and molds on heat-resistant materials. Contamination control during the incubation of cell cultures in a CO₂ incubator is of the greatest importance.
The standard settings for a hot air oven are: 1.5 to 2 hours at 160 °C (320 °F) 6 to 12 minutes at 190 °C (374 °F)
Examples of items that aren’t sterilized in a hot air oven are surgical dressings, rubber items, or plastic material.
A hot air oven is a type of dry heat sterilization.
Items that are sterilized in a hot air oven include:
Glassware (like petri dishes, flasks, pipettes, and test tubes)
Powders (like starch, zinc oxide, and sulfadiazine)
Materials that contain oils
Metal equipment (like scalpels, scissors, and blades)
Hot air ovens are electrical devices which use dry heat to sterilize. They were originally developed by Louis Pasteur. Generally, they use a thermostat to control the temperature.
The oven begin to heat automatically with ‘PV’ showing present temperature in the chamber and ‘SV’ showing the target temperature the oven will reach to.
For the calibration of hot air oven use a standard thermometer ranging up to 300º C. 5.2 Start the calibration procedure after 1 hour of staring the oven. Set the oven at desired temperature. 5.4 Put the standard thermometer for 30 minutes on the upper shelf of the oven and close the door of the oven.
Autoclaving refers to a process of instrument sterilization that uses time, temperature and pressure to kill all forms of microbial life, whereas dry heat sterilization is basically sterilizing using an oven that uses time and heat to kill all forms of microbial life, including microbial spores and viruses.
Due to the excessive temperatures used in dry heat, Bacillus atrophaeus spores are used to monitor the efficiency of the sterilization process.
- Alkadhim, Saif Aldeen Saad, Hot Air Oven for Sterilization: Definition & Working Principle (December 14, 2018). Available at SSRN: https://ssrn.com/abstract=3340325 or http://dx.doi.org/10.2139/ssrn.3340325
- Types of Ovens, ProSciTech Pty Ltd, 2014-06-05, Available at https://laboratoryresource.com/?navaction=getitem&id=204
- Use of Hot air oven in laboratories, prestogroup, available at https://www.prestogroup.com/blog/use-of-hot-air-oven-in-laboratories/