Dry Heat Sterilization: Definition, Process & Validation

Instructor: Alexandra Unfried

Alexandra earned her master's degree in nursing education and is currently a hospital supervisor/administrator.

Dry heat sterilization is used to decontaminate objects and spaces. This lesson will discuss the meaning of, process, and validation of dry heat sterilization.

Sterilization

Kathy has just started working at a hospital in the infection control department. She is getting to know the decontamination processes of the operating room regarding equipment. Kathy wants to make sure that the equipment is functioning properly and that infection rates decrease. Today she is investigating the dry heat sterilization procedures.

How does Dry Heat Sterilization Work?

Dry heat sterilization uses high temperatures to kill microorganisms and bacterial spores. Another type of sterilization by heat uses moist heat. Both are acceptable and used to sterilize different types of equipment. Dry heat sterilization requires higher temperatures and longer exposure times than moist heat sterilization. Recommendations are:

Temperature Exposure time
150 degrees Celcius 150 minutes
160 degrees Celcius 60 minutes
170 degrees Celcius 30 minutes

Dry heat sterilization is used on items that cannot get wet and for glassware, oils, powders, metal instruments, and items wrapped in paper. There are several different types of dry heat sterilization such as:

  • Hot air oven: there is static air (heating coils on the bottom) or forced air hot air oven (motorized blower) that are used differently
  • Incineration: burns medical waste that is disposable
  • Flaming: exposing objects to direct fire/flame

Example of a hot air oven for dry heat sterilization
Example of a hot air oven for dry heat sterilization

Kathy is reviewing the process of sterilizing reusable medical equipment in the operating room so she is focusing on the use of the hot air oven.

Process of Using a Hot Air Oven

The hot air oven is the most commonly used form of dry heat sterilization. It is a large container that holds several objects. Once the oven is filled, it is closed and secured for the allotted time it will take to sterilize. For example, the oven is set at 160 degrees Celsius so it will not be opened until 60 minutes has passed. A hot air oven does not harm any of the objects that are being sterilized and it is non-toxic to the environment. However, it is time consuming and requires extremely high temperatures.

Static Air Hot Air Oven

A static air hot air oven is not as commonly used as forced air. The oven has coils on the bottom to heat the oven. It takes a long time for the temperature to be reached because the hot air has to rise through convection. This also means that the temperature may not be uniform throughout the oven.

Forced Air Hot Air Oven

A forced air hot air oven is a better choice than static air. It uses a motorized blower to distribute the heat throughout the oven. Therefore, forced air is more efficient at equally distributing hot air in the oven and does not take as long as static air.

Kathy finds out that the hospital uses forced air hot air ovens. The machines appear to be in good condition and are working correctly. She is ready to see if they are successful at completing the sterilization process.

Validation

Validation is tested on each dry heat instrument to make sure it is working effectively. A document of validation tests temperature control, air particulate levels, and the process to destroy bacteria and other contaminants. It is a requirement by the Food and Drug Administration (FDA), International Organization for Standardization (ISO), United States Pharmacopeia (USP), and American National Standards Institute (ANSI). There are four types of validation which include:

  • Installation qualification: documents that the dry heat instrument is installed correctly according to manufacturer guidelines; checks calibration, instrument valve information, utilities, and standard operating procedures
  • Operational qualification: validates the equipment is working as intended; checks that alarm settings, control functions, and equipment are meeting the sterilization goal
  • Performance qualification: shows the machine works as intended repeatedly and that the temperature remains constant over time
  • Temperature mapping: small instruments called data loggers are dispersed throughout the oven to detect temperature; must be successfully recorded at least three times to be validated

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