What Is Dry Heat Sterilization?

Dry heat sterilization generally involves placing an item to be sterilized inside an oven or heat chamber, and heating it until it is warmed all the way through. This process usually kills infectious organisms, even in porous materials like pottery. Many people use dry sterilization as an alternative to boiling for items that cannot get wet, such as water-soluble powder, oil, or items prone to oxidization.

Those that eschew dry heat sterilization in favor of other methods may not understand exactly how it works. This method must be used properly to achieve a completely clean item. It also takes some time, and one to two hours are typically necessary for full sterilization, depending on the temperature used. An ordinary convection oven, or even a toaster oven, may be used for this process. The item or items to be cleaned must be placed on a clean surface, not directly on the oven rack. This helps prevent any organisms already in the oven from being transferred to the item.

Oils, powders, and other non-solid items should be placed in a clean, heat-safe container before being subjected to dry heat sterilization. The oven should be preheated to 320° Fahrenheit (160° C) for sterilization in two hours, or 340° F (170° C) for sterilization in one hour. Preheating should be done for about 20 minutes before the object is placed inside the oven, to help ensure that the oven is hot enough to do its job. The item should then be placed on the center rack of the oven and left to heat.

After the item is heated, it should be allowed to cool inside the oven for an hour or two. This prevents the item from being contaminated as it cools. The user should then remove the item from the oven with a clean, heat-safe glove. Medical instruments and items used in lab experiments are sometimes sterilized this way. Laboratories often contain large chambers for dry heat sterilization, in which sterilized vents blow superheated air into the chambers and clean the items inside.

When sterilizing many items at one time, they should generally be placed in the oven spaced about 6 inches (about 12 cm) apart. This allows the warm air to flow freely around the items, which is necessary for proper sterilization. Those who don’t ascribe to dry heat sterilization generally dislike it because it can take a very long time if many items need to be sterilized.