Dry Heat Sterilization

Sterilization is one of the most important procedures in medical field and food related industries. Microbes like fungi, viruses, bacteria and spores pervade all space and thrive wherever they find favorable conditions. Sterilization is any kind of process that is aimed at eliminating or neutralizing these harmful pathogens from any kind of surface, food item, medical equipment or any other material. Dry heat sterilization is one such method that is aimed at sanitizing materials. In this article, I provide a brief overview of the dry heat sterilization method for your perusal.

What is Dry Heat Sterilization?
Dry heat sterilization is one of the first sterilization methods developed in industries. It 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 being sterilized through conduction. The heat first permeates the surface layers and then progressively enters deeper layers of the material. After a sufficiently long period of time, the whole substance is heated to a high temperature and the pathogens are destroyed as a result of protein coagulation, brought about by the heat.

Dry heat sterilization is used only on materials that can withstand heat till high temperatures. There are records of dry heat sterilization being used by the Romans in their medicinal and surgical procedures. Since then, as civilizations realized the importance of hygiene and sterilization, new methods were developed according to the means available in those times. Medical instruments like hypodermic needles are generally subjected to dry heat sterilization.

Normally, in a dry heat sterilization process, the material are subjected to heated air at a temperature of 160^o C for two hours at a higher temperature of 170^o C for just one hour. The materials or instruments that are to be sterilized should be dry before being placed in the sterilization oven. One of the most important aspects of dry heat sterilization 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.

Types of Dry Heat Sterilization Methods
The heat moves around in the interior of a chamber through the process of convection. It is a process of hot air rising and cooler air descending to displace it. Based on this aspect, there are two dry sterilization methods that are employed. One is the gravitational convection based dry heat sterilization method and the other is mechanical convection based dry heat sterilization.

In the former one, the convection of hot air occurs under gravity as hot, lighter air rises and cold, heavier air descends. This process of convection is slower and it takes a lot of time for a uniform temperature to be achieved. The latter process involves forced convection of hot air with the use of blowers. This mechanical convection based sterilization process is more efficient compared to the former one. It is widely used in the sterilization of medical surgical instruments, that require a high level of hygiene to be maintained.

Dry heat sterilization and other sanitizing methods play an increasingly important role in the medical product 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 dry heat sterilization, other sterilization methods involve subjecting materials to irradiation, high pressure, filtration and chemicals. Hope this article has sufficiently clarified the process of sterilization by dry heat.