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Dry Heat Sterilization and Steam Sterilization

Dry Heat Sterilization and Steam Sterilization share the common goal of eradicating microorganisms to ensure the sterility and safety of diverse materials and equipment.

Sterilization is a way of super cleaning to eliminate tiny germs that can cause illness. Two options to achieve this is to use heat that does not contain drinking water (dry heat) and steam (hot water vapor). Dry heat is similar to baking in an oven with very high temperatures.

Steam is similar to using hot, humid air to cleanse. Both are effective in killing germs, they operate differently and are utilized to accomplish different tasks. Dry heat is slower and requires higher temperatures, while steam is quicker and is able to clean certain things which dry heat won’t.

Knowing these differences will help us to determine the best method to wash different things and protect us from germs. 

What is Dry Heat Sterilization?

Dry sterilization by heat is a technique to clean things through high-temperature heating without water. It’s similar to giving things the most intense heat treatment in order to eliminate tiny bacteria that can cause us to become sick.

Steam Sterilization
Figure 01: Dry Steam Sterilization

This method does not require water, as opposed to those who use steam or hot water to wash. There are two kinds of dry sterilization using heat. The first is with hot air ovens. They function as extremely hot ovens that blow air at 350-375 degrees Fahrenheit (or 160-190 degrees Celsius) for several hours.

The super-hot air kills bacteria by altering their proteins and then burning them. Another type of incineration involves burning materials at extreme temperatures until germs are completely melted to ashes.

Dry sterilization using dry heat is ideal for items like glassware or metal tools, oils, and powders that are able to withstand high temperatures without being damaged. It takes however more time and requires more heat in comparison to other methods such as steam.

What is Steam Sterilization?

Steam sterilization also referred as autoclaving is a method of cleaning objects making use of hot, humid gas (steam) to kill small bacteria that can cause us to get sick. It’s similar to using extremely hot water to ensure that everything is clean.

Steam Sterilization
Figure 02: Steam Sterilization

The process involves placing objects in a specific autoclave, which makes use of high-pressure steam at extremely high temperatures, typically between 121-134 degree Celsius (250 -273° Fahrenheit) for a specified period of duration.

The high temperature and pressure generated by steam kill viruses, bacteria along other microorganisms that can cause harm that are on the products and make them safe to use.

Steam sterilization is widely employed in labs, hospitals, and other sectors where cleanliness is essential due to its speed and effectiveness and is able to clean kinds of things such as surgical instruments medical equipment, surgical instruments, and even a variety of materials and clothing.

Key Difference Between Dry Heat Sterilization and Steam Sterilization

The key differences between dry heat sterilization and steam sterilization:

Aspect Dry Heat Sterilization Steam Sterilization (Autoclaving)
Principle Uses high temperatures without moisture Uses steam under pressure
Mechanism Denatures proteins, disrupts cell membranes Penetrates materials denatures proteins
Temperature Range 160°C to 190°C (320°F to 375°F) Around 121°C (250°F) at 15 psi
Exposure Time Longer exposure time required Shorter exposure time
Materials Compatibility Suitable for heat-resistant items, metals, glass Suitable for a wider range of materials
Effectiveness Effective against certain organisms, slower process Effective against various microbes, rapid process
Equipment Dry heat ovens or chambers Autoclaves equipped with pressure and steam system
Challenges Longer processing time, limited material compatibility Potential for moisture-related damage, careful loading required
Applications Laboratory equipment, certain pharmaceutical items Medical instruments, surgical tools, laboratory and hospital settings
Validation & Monitoring Temperature monitoring, validation protocols Biological indicators, temperature checks

How Dry Heat Sterilization Works?

Here’s an explanation of the ways that dry heat sterilization works:

  • The application of heat: Dry sterilization typically takes place within an oven or heated space. Conduction transfers heat to the objects that require sterilization.
  • temperature control: The process involves higher temperatures, which typically range between 160degC and 190degC (320degF to 350degF). Some procedures might even demand higher temperatures for shorter periods.
  • Time: Compared to methods that use dry heat, moist sterilization of heat requires longer exposure times because of lower heat transfer. Things are typically exposed for a period of time according to the temperature you choose.
  • Microbial Termination: The higher temperatures experienced that are produced during dry heat sterilization result in irreparable harm to microorganisms. Proteins break down and cell membranes degrade and the essential cell components become damaged which leads to deaths of microorganisms, as well as spores.
  • uniform heating: ensuring even distribution of heat across the load is essential for ensuring effective sterilization. Some dry heat sterilizers incorporate mechanisms or fans to ensure uniform heating.
  • The Cooling phase: When the sterilization process, items go through a gradual cooling process within the sterilizer to avoid thermal shock that could cause harm to sterilized products.
  • Verification and monitoring: Continuous verification as well as monitoring the sterilization process is vital. This means using biological indicators as well as monitoring temperature and adhering to established procedures to ensure the effectiveness of the sterilization process.

Types of Dry Heat Sterilization

Dry heat sterilization is a variety of types of methods to remove microorganisms from objects without the use of moisture. A few common dry heat sterilization techniques include:

  • Heating Oven: This method uses an oven that circulates hot air at temperatures of 160-190° Celsius (320 to 325 degrees Fahrenheit) for a prolonged period. Things placed inside the oven are heated to the heat which kills microorganisms.
  • Incineration: This process involves placing items under extremely high temperatures, usually directly exposed to intense heat or flames. The intense temperatures burn and kill microorganisms by burning them into ashes.
  • Dry Heat Tunnel Sterilization: It’s a method that is used in the pharmaceutical sector in which packages or products move through a tunnel heated, subjecting them to the dry temperature for a specific time period, which ensures sterilization.
  • Flaming: The Flaming method is a simple and rapid dry heat sterilization technique that can be used to sterilize small instruments like metal wires or inoculating loops found in labs. The object is then briefly passed through a torch to kill microbes.

Which Items are Suitable for Sterilization using Dry Heat Methods?

“Items that can withstand high temperatures without getting damaged are suitable for sterilization using dry heat methods. These may include glassware, metal instruments like forceps or scalpels, certain types of powders, oils, and materials that are not sensitive to heat or moisture.

Dry heat sterilization is ideal for items that might corrode, rust, or be negatively affected by exposure to moisture, making it a good choice for certain laboratory equipment and metal tools.”

Which type of Plastic can be used with Steam Sterilization?

The most common plastics that are suitable for steam sterilization are:

  • Polypropylene (PP): This plastic is well-known for its resistance to heat and is frequently utilized in medical and laboratory environments for things like pipette tips, containers, and laboratory equipment.
  • Polycarbonate (PC): PC is a different heat-resistant plastic that is commonly used to make laboratory equipment, such as beakers and petri dishes, as well as certain components of medical devices.
  • Polyethylene Terephthalate (PET also known as PET): While PET isn’t as heat-resistant like other plastics it is often able to withstand steam sterilization for shorter periods with lower temperatures.
  • Polyether ether Ketone (PEEK): PEEK is a high-performance material that has excellent chemical resistance and is able to withstand extreme temperatures, which makes it ideal for certain processes of steam sterilization.

What are the Steps of Steam Sterilization?

Below are some steps required for steam sterilization:

  • Preparation of Items: Make sure that the items you intend to sterilize are suitable for autoclaving as well as in a state that is compatible with the heat and humidity involved during the process. It is important to arrange the items in a manner so that steam can penetrate and also the distribution of heat.
  • loading into the Autoclave: Place the items within the autoclave chamber, making sure there is an appropriate spacing between the items and making sure that there isn’t any overcrowding. A proper loading process ensures effective steam circulation and thorough sterilization.
  • The addition of water: Distilled water is usually added to the reservoir of an autoclave to produce steam. The quantity of water to be added must be in line with the instructions of the manufacturer to ensure the pressure required for steam.
  • Settings Parameters: The sterilization settings like temperature or pressure, as well as exposure time according to the requirements specific to the items to be sterilized. The most common parameters are the temperature of about 120degC (250degF) and an average pressure of 15psi (pounds for every sq inches) for a period that is determined by the type of load and objects.
  • Beginning Cycle: Begin the autoclave cycle and allow the chamber to fill up with steam until the desired temperatures and pressures are met. The sterilization process typically involves heating then exposure at the set temperature, and sustaining temperature and pressure for the specified time.
  • The Sterilization phase: The items remain exposed to steam at high pressure for the specified period. This stage ensures the destruction of microorganisms like bacteria and fungi, viruses, and spores, which effectively sterilizes the products.
  • The Cooling phase: When the sterilization process the autoclave reduces the pressure and allows it to cool. A slow cooling process helps prevent damage from thermal shock as well as to the items sterilized.

Types of Steam Sterilization

Here are a few common variations or aspects of steam sterilization:

  • Gravity Displacement Autoclaves: These autoclaves make use of steam to remove air from the chamber and allow steam to enter and sterilize the items. They are commonly employed in hospitals as well as laboratories to sterilize surgical instruments, glassware as well as laboratory equipment.
  • Vacuum Autoclaves: Vacuum autoclaves take all air in the room prior to injecting steam. By removing air, you create the most effective sterilization conditions which is particularly beneficial for porous materials or materials that can hold air pockets.
  • Pre-vacuum Autoclaves: These autoclaves start by creating an atmosphere of vacuum to eliminate air and then introduce steam to sterilize. This method is very effective in sterilizing wrapped products or other materials that may not allow steam to penetrate.
  • Continuous Steam Sterilizers with Flow: This method involves a continuously flowing stream of steam that is able to flow through the materials that are being sterilized. It is often employed in industries such as food processing or pharmaceuticals to ensure the sterilization of liquids, or for large quantities of substances.


Steam sterilization and heat can be used to wash objects and kill germs which can cause illness. Dry heat utilizes extremely hot temperatures, with no water, such as a very hot oven or a fire to kill germs that are on objects.

Steam sterilization, also referred to as autoclaving, utilizes steam that is hot and wet, also known as steam from a specially-designed machine to cleanse things making use of high-pressure steam at extremely high temperatures.

Dry heat is great for objects that can take high temperatures without being damaged like tools made of metal and glassware. Steam sterilization is more efficient and is able to clean various items like surgical instruments as well as medical equipment and certain kinds of clothing.

By sourav