All About ETO Sterilization with ETO Sterilizer

Sterilization is a process which eliminates, removes or kills all form of microbial life including fungi, bacteria, viruses, etc. Microbial life thrives everywhere; on the surface, in fluids, in medication, on food. Various means of sterilization available are: Heat, Chemical, Radiation, Pressure and Filtration. ETO sterilization is one of the most widely used sterilization methods. It is a chemical form of sterilization and provides high efficiency with deep penetration power. Because of this ETO is preferred for sterilization of Medical and Pharmaceutical Products.

What is ETO?

ETO or Ethylene Oxide is a colorless and flammable gas having a faintly sweet odor. The chemical structure of the compound has a strained ring that makes it participate quite readily in the addition reactions causing the ring (of the structure) to open. The ethylene oxide sterilization or ETO sterilization is primarily used to sterilize the medical & pharmaceutical products. It kills the microorganisms that is accumulated during the production or packaging process. Apart from microorganisms, ETO also kills the spores. It is basically used to sterilize items that are heat or moisture sensitive and is suited for semi-industrial applications.

ETO sterilizer carried out the process in 3 stages, namely- Pre Conditioning, Sterilizer, Degasser. In the pre conditioning stage, the batch is made to stay under an environment of controlled temperature and humidity. For the sterilizer stage, the system requires an accurate temperature control and pressure & vacuum control. The actuators require security interlocks. This stage also include checking for tolerance change, phase changes, etc. In the degasser stage, the products are degassed to remove any remaining particles of ETO. The entire batch is made to dwell under the temperature controlled environment.

What is ETO Sterilization?

ETO Sterilization, also known as Ethylene Oxide Sterilization, is a chemical process done with the device called ETO Sterilizer. The primary factors affecting this process include chemical concentration, humidity, temperature and time. ETO is a colourless and odourless gas and is used as a low-temperature sterilant. It is considered to provide sterilization as a result of alkylation of protein, DNA and RNA. This prevents cellular metabolism in microbial life and also prevents them from replicating. ETO gives more effective results by penetrating through most materials including plastics.

Why and Where ETO Sterilization is used?

For industries like Pharmaceuticals, it has become essential to perform sterilization to avoid contamination. Even plastics and Electronics industries are praising this method. Other methods of sterilization available, for example, steam; is cost-effective but will damage sensitive materials like biological materials, fibre, electronics and plastics. For such materials, chemical sterilization methods are preferred which has high penetration power and gives no damage. Sterilization of tools and other materials in any medical procedure is very essential. As these materials are delicate ETO process is preferred. Similar usage of this process can be seen in different places including hospital, electronics industry, plastic industries, etc.

ETO Process for pharmaceutical products:

ETO is a colourless and odourless gas and has high penetration power. It is highly explosive so it should be handled with care. For its non-damaging effects, it is readily used in sterilization of pharmaceutical materials. A series of steps need to be followed to perform sterilization using ETO.


Like most other sterilization processes, ETO sterilization process starts with preconditioning of products that are to be sterilized. Preconditioning is usually done in a separate room or specially designed room for preconditioning. In this process, the product is heated and humidified at a stable internal temperature and moisture. The preconditioning step assures that the sterilization process is reproducible regardless of external atmospheric condition. After preconditioning, the product is placed in a heated chamber.

2.Initial Evacuation:

This step involves removal of most of the air from the chamber. It is done to ensure the safe use of ethylene oxide and hence safely deliver the results. Evacuation of air from the chamber is usually accomplished by performing deep pumping using a vacuum pump. The same results can also be achieved by performing a series of partial vacuums and a series of nitrogen injections. This two steps combined, when performed repetitively, will the air.


During the preconditioning step, the heat was applied to the product. This may lead to loss of a significant amount of moisture from the product. This loss of moisture can affect the final results hence it is necessary to provide additional moisture. The amount of moisture required is determined and the same is injected in form of steam injections. After injecting the steam, the product is left for some time to soak the moisture and replace the lost moisture.

4. Gas Injections:

The next step is an injection of ETO gas in the chamber. Since ETO is available in the liquid state, it has to be heated into gaseous state first, before injecting it into the chamber. This step involves a long and complex sterilization cycle and requires a system with:

  • Accurate temperature control
  • Reliable control systems
  • Advance reporting and warning systems
  • Shutdown strategies in critical conditions

The concentration of the gas to be injected depends on two primary factors. The first factor is the minimum amount of gas that is required to attain complete sterility of the product. The second factor is the maximum amount of gas that can be injected without causing any difficulty due to high levels of EO-residuals. After the injection of gas; the product is exposed to heat and humidity for q certain period of time. The exposure time depends on the difficulty of sterilization of product. The more difficult the product is to sterilize, the longer the exposure time.

5.Post-exposure Gas Purge:

Once the gas injection process is complete, all gas from the chamber is removed. This is done because ETO is highly flammable, so to ensure safety the level of gas should be below the flammable limit.


Once the ETO sterilizer completes the sterilization, products are placed in a room with elevated temperatures. In this room, airborne residue gases are contained and removed continually.

What is Ethylene Sterilization process used For?

ETO sterilizers are widely used in the pharmaceutical industry to sterilize products sensitive to moisture or heat. Ethylene oxide can penetrate multiple layers of breathable packaging, which makes it suitable for the sterilization of a wide range of materials:

  • Assembled complex devices
  • Catheters
  • Syringes
  • Saline bags
  • Stents
  • Multi-lumen tubing products
  • Products with integrated-electronics
  • Custom procedure packs

An effective ETO process can be designed for almost all types of medical devices and permeable packaging configuration, if the variables are assessed through thorough process design and development.

Advantages of this method:

  • This sterilization is carried out at low temperatures. Many other sterilization methods involve the use of extreme heat which might damage the products.
  • Its non-corrosive nature makes it preferable for sterilizing metal, plastic and rubber.
  • Its high penetration capacity makes it very efficient.
  • It can be used to sterilize a large number of products.

Challenges to be faced during ETO sterilization:

  • The chemical used is harmful to humans, so the procedures should be carried out carefully.
  • Flammable nature of ETO gas raises safety concerns.
  • The time required for the sterilization process is high.
  • Requires strict environment causes the overall cost to rise.