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What is Dry Heat Sterilization and Why is it Important?

Dry Heat Sterilization
Dry heat sterilization is one of the oldest methods used for sanitizing materials. Here, we provide information about this process.
Omkar Phatak
Last Updated: Mar 19, 2018
Bacteria, viruses, fungi, and spores are pathogens that thrive wherever they find favorable conditions. Sterilization is a process that is aimed at eliminating or neutralizing these harmful pathogens from any kind of surface, food item, medical equipment, or any other material. The term 'dry heat sterilization' refers to the process of sanitizing materials or freeing them from these pathogens by using heat.
What is Dry Heat Sterilization?
This method is commonly used in industries, and involves the extermination of harmful pathogens by subjecting materials to blasts of heated air, with little or no moisture, for long periods of time. Heat is absorbed by the material that is being sterilized through conduction. The heat first permeates the surface layers. Thereafter, it progressively permeates the deeper layers of the material. After some time, the whole substance is heated to a high temperature. The pathogens are destroyed as a result of protein coagulation that is brought about by the heat.
This type of sterilization is only used on materials that can withstand high temperatures. There are records of this sterilization method being used by the Romans in their medicinal and surgical procedures. As civilizations realized the importance of hygiene and sterilization, newer methods were developed according to the means available in those times. Medical instruments like hypodermic needles are generally subjected to sterilization by dry heat.
Normally, in a dry heat sterilization process, the material is subjected to heated air at a temperature of 160°C for two hours, and at a higher temperature of 170°C for just one hour. The materials or instruments that are to be sterilized should be dry before they are placed in the sterilization oven. One of the most important aspects of this method is that the heating needs to be uniform, and a consistent temperature needs to be maintained. Also, the oven itself should be cleaned periodically. Sometimes, the items may be wrapped with a foil or muslin cloth before being placed in the sterilization chamber.
The heat moves around in the interior of a chamber through the process of convection. So, the hot air rises and cooler air descends to displace it. Based on this aspect, there are two methods that are employed. One is the sterilization method that is based on gravitational convection, and the other method is based on mechanical convection.

In case of the former, the convection of hot air occurs under gravity as hot, lighter air rises and cold, heavier air descends. This process of convection is slower; it takes a lot of time for a uniform temperature to be achieved.
sterilizing surgical packs
The latter involves the forced convection of hot air with the use of blowers. This process is more efficient in comparison to the former. It is widely used in the sterilization of medical surgical instruments, as these instruments require a high level of hygiene to be maintained.
On a concluding note, dry heat sterilization methods play an increasingly important role in the medical or pharmaceutical industries, which put a premium on the safety and purity of their products. The level of sterilization achieved is measured by the sterility assurance level, which is a probabilistic way of measuring sterilization in products. Other than this, other sterilization methods involve subjecting materials to irradiation, high pressure, filtration, and chemicals.