What is Dry Heat Sterilization

Dry heat sterilizers are the most commonly used sterilization equipment in pharmaceutical, laboratory and medical facilities. It utilizes high temperature dry heat air to kill microorganisms. Sterilization is an important part of ensuring the sterility of items and environments in medical, laboratory and industrial settings. The process of dry heat sterilization is relatively simple, but requires precise control of temperature and time to ensure thorough sterilization. This article will detail the principles, advantages, etc. of dry heat sterilization to provide readers with a comprehensive perspective for an in-depth understanding of this technology.

How Dry Heat Sterilization Works

Dry Heat Sterilization, as a classic high-temperature disinfection method, is widely used for the disinfection of items that need to kill microorganisms and are resistant to high temperatures. The principle is that hot air directly destroys the cell walls and proteins of microorganisms at high temperatures, rendering them inactive and incapable of reproduction, thus achieving complete sterilization. Unlike wet heat sterilization, dry heat sterilization does not need to rely on water vapor and is more suitable for dealing with items that are afraid of moisture and resistant to high temperatures, such as glassware, metal utensils and certain powdered materials.

Dry Heat Sterilization Process

Dry heat sterilization relies on heat conduction and convection. In this process, items are heated for decontamination using a hot air sterilizer. The item inside the sterilizer absorbs the heat, thus eliminating any pathogens on the item. The process uses specific time and temperature calculations to eliminate pathogens. If the time-temperature relationship is broken or incorrect, the item may not be sterilized.

The success of dry heat sterilization relies on precise temperature control and sufficient time to ensure that all microorganisms, including the most heat-resistant spores, are completely killed. The following are specific steps for dry heat sterilization:

1. Clean the items to be sterilized

2. Place the items, making sure to leave enough space between them so that the hot air can circulate evenly.

3. Set the sterilization parameters (temperature and time)

4. Dry heat sterilization is usually performed in the following temperature-time ranges:
   160°C: at least 2 hours
   170°C: at least 1 hour
   180°C: at least 30 minutes

5. Do not open the sterilizer during the cycle. Opening the door will interrupt the sterilization process and disrupt the progress of the cycle.

6. Once sterilization is complete, cool before removing the unit.

7. After cooling is complete, remove items in a sterile environment to prevent contamination. If items are packaged, they can be stored directly in the sterile area.

Difference between moist heat sterilization and dry heat sterilization

There are several processes that can be used to sterilize different materials. In order to be able to choose the correct sterilization process, it is important to know which method is more suitable for the material in question. You cannot use an autoclave to sterilize heat sensitive materials. Similarly, you cannot filter sterilize chemicals that have a larger microbial size compared to the membrane pores of the filter.

Therefore, in order to effectively use dry heat and moist heat sterilization, the differences between the two are described next.

Moist Heat Sterilization

Moist heat sterilization uses high pressure water, the steam temperature in this method is lower compared to dry heat sterilization, but the high pressure helps in effective sterilization.

Moist heat destroys the structural proteins and enzymes of the organism, leading to its death. Moist heat is suitable for heat-sensitive materials and materials where steam is permeable. Culture media can also be sterilized by moist heat sterilization.

By moist heat sterilization, the most resistant spores require a temperature of 121°C for about half an hour. This is a more efficient method than dry heat sterilization.

Dry Heat Sterilization

In dry heat sterilization, dry heat is used to sterilize different materials. Dry heat helps to kill the organisms using destructive oxidation method. The basic components of the cell are destroyed and the organism dies. The temperature is maintained for nearly an hour to kill the most difficult to kill resistant spores.

Items such as glassware, metal instruments, paper wrappers and syringes can be effectively sterilized by dry heat sterilization. The materials used for these items are heat-resistant or can be described as heat-stable. Impermeable powders and anhydrous fats and oils can also be sterilized using dry heat sterilization.

Advantages of dry heat sterilization:

1. Dry heat ovens are generally less expensive.

2. The cost of running and heating cycles is usually low.

3. Heat can penetrate deep into thick objects for deep sterilization, even inside packages.

4. Metal objects with good heat resistance can be quickly sterilized at high temperatures.

5. Dry heat has no corrosive effect on metallic materials because they contain so little moisture.

6. The process does not involve any toxic agents and therefore does not release any harmful substances into the environment.

7. No human supervision or intervention is required during operation. All that is required is for someone to set the oven and allow it to complete the entire cycle.

8. Since the object cools quickly, it can be removed and used almost immediately.

Disadvantages compared to other processes:

1. Dry heat sterilization takes much longer than steam, flame, chemical sterilization or radiation.

2. Heat may cause sensitive materials or sheets to warp.

3. High temperatures can cause irreversible damage to plastics and rubber, so these materials are not suitable for dry heat.

4. Even for materials that can withstand high temperatures, overexposure to high temperatures can lead to unwanted changes in the chemical structure of certain substances.

Conclusion

Dry heat sterilization is a reliable autoclave sterilization method widely used in medical, laboratory and industrial applications. Although it has the shortcomings of high energy consumption and long time, it has unique advantages in handling glassware, metal utensils and moisture-intolerant items. In the future, with the progress of science and technology, dry heat sterilization technology will make greater breakthroughs in the direction of energy saving, automation and environmental protection, and provide more efficient solutions for the aseptic protection of various industries.