Difference Between Dry Heat Sterilization and Moist Heat Sterilization

Difference Between Dry Heat Sterilization and Moist Heat Sterilization

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Today we will discuss the Difference between Dry Heat Sterilization and Moist Heat Sterilization and their advantages and disadvantages, types.

So, friends let’s start with the definition of Moist heat sterilization and dry heat sterilization.

Moist Heat Sterilization:

Moist heat sterilization involves the use of steam in the range of 121-134˚C.

Steam under pressure is used to generate high temperatures required for sterilization. Saturated steam acts as an effective sterilizing agent.

Moist heat sterilization is important for sterilizing instruments like manufacturing utensils, tray, garments, etc.

During this kind of sterilization process, the autoclave is employed, where the pressure of the steam with relatively warm temperature (though lower than the dry heat sterilization) is employed.

In this type of sterilization, the moist heat (steam) sterilizes the equipment or utensils by denaturalizing the enzymes and therefore the structural proteins of the harmful microbes existing on the equipment and hence killing them.

The moist heat directly destroys the proteins of the microbes by the coagulation of microbes. Desired timing is about 15 to 30 minutes at a temperature of 121°C.

Advantages of the Moist Heat Sterilization:

  • Requires coldness.
  • Less time to finish.
  • Easy to manage and monitor.
  • Low cost
  • Non-toxic

Disadvantages of the Moist Heat Sterilization:

  • After sterilization, the instrument remains wet, which can result in rust.
  • Chance of instrument damaged, because of repeated exposure.

Articles Sterilized:

  • Culture media
  • Bandages
  • Equipment
  • Pharmaceutical products etc.

Precations:

  • The autoclave should not be too much overloaded.
  • Air discharge must be complete and no residual air trapped inside.
  • Caps of bottles and flasks should not be tight.
  • The autoclave does not open until the pressure not to be down.
  • Articles must be wrapped in a proper manner to prevent drenching,
  • Bottles should not be too much overfilled.

Dry Heat Sterilization:

Dry heat sterilization is one of the old techniques to sterilize the glassware and other equipment.

During this method, heated air of warm temperature is used and further, the method is the same as that of the conduction method.

Heat is absorbed from the encircling area of the equipment and is moved forward to the following layer, and slowly the entire equipment gets heated and attains sterilization.

The holding period may vary from 1 hour to 2 hours together with the temperature of the 160°C to 170°C correspondingly.

The temperature is beyond the moist heat sterilization process; there are more chances of the microbes to urge the kill.

Incineration, the high flame is that the different kinds of processes performed under dry heat sterilization. Though this method takes more time as compare to moist heat sterilization.

Types of Dry Heat Sterilization:

RED HEAT:

Articles such as bacteriological loops, straight wires, tips of forceps, and searing spatulas are sterilized by holding them in Bunsen flame till they become red hot.

This is a simple method for effective sterilization but it is limited for those articles that can be heated to redness in flame.

FLAMING:

This is a method of passing the article over a Bunsen flame, but not heating it to redness.

Articles such as scalpels, test tubes, flasks, glass slides, and coverslips are passed through the flame a few times.

This method too is limited to those articles that can be exposed to flame, also cracking of the glassware may occur.

INCINERATION:

This is a method of destroying contaminated material by burning them in incinerators.

Articles such as soiled dressings, animal carcasses, pathological material, and bedding, etc.

This technique results in the loss of the article hence are suitable only for those articles that have to be disposed of.

Burning of polystyrene materials emits dense smoke, and hence they should not be incinerated.

HOT AIR OVEN:

Articles to be sterilized are exposed to high temperatures (160°C) for a duration of one hour in an electrically heated oven.

Air is a poor conductor of heat, even distribution of heat throughout the chamber is achieved by a fan. The heat transfer in the article occurs through the radiation, conduction, and convection method.

The oven should be fitted with a thermostat sensor to control the temperature indicator. Meshed shelves must have proper insulation on the door.

Advantages of Dry Heat Sterilization.

  • Reliable.
  • Nontoxic.
  • Low cost and is straightforward to put in.
  • As the instrument remains dry after sterilization,
  • No chances of corrosion.
  • Not harmful to the environment.

Disadvantages of the Dry Heat Sterilization

  • It requires a longer time than sterilization.
  • Exposure to the higher temperature is also damaging to the instrument.

Key differences between the Moist Heat and Dry Heat Sterilization:

S. No. BASIS FOR COMPARISON MOIST HEAT STERILIZATION DRY HEAT STERILIZATION
01 Process
  • Moist heat Sterilization work on a low temperature and high-pressure of water or steam.
  • Dry Heat Sterilization work on the dry air of high temperature and for a longer time duration.
02 Main Requirement
  • It needs steam and water.
  • There is no use of steam and water.
03 Sterilization Process 
  • Coagulating protein of the microbes very effectively.
  • Oxidation of the protein and other chemical bonds present in microbes.
04 Pressure
  • Performed under pressure.
  • Performed on direct flame.
05 Time Required to Complete the Process
  • Moist heat sterilization complete in less time.
  • Complete in more time relatively.
06 Mechanism
  • Moist sterilization work on coagulation.
  • Its coagulation of protein and enzymes of the microbes.
  • The process is more effective.
 

  • Dry heat sterilization work on the oxidation process.
  • It kills the microbes by the oxidation of microbes protein and chemical bonds present in microbes.
07 Timing
  • Takes less time
  • Takes more time
08 Equipment 
  • Autoclaving and Boiling is an example.
  • Incineration, Bunsen burner (flame), Hot air oven and Microwave is an example.

Thank you so much for reading “Difference Between Dry Heat Sterilization and Moist Heat Sterilization”

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