When a hydrogen peroxide solution is vaporized, its molecules are freed from one another to travel the world in gaseous form. In an SPD, this world they travel is the chamber of a low temperature sterilizer and the medical devices it contains. This gaseous state allows the reactive H2O2 molecules to reach deep into these medical devices and find bugs hidden in lumens, cracks, and crevices. Hydrogen peroxide sterilizers start their cycles by removing air from the sterilization chamber to achieve a deep vacuum. The H2O2 solution is then vaporized with heat and introduced inside the sterilization chamber, followed by a waiting period allowing the H2O2 molecules to do their remarkable job. The vacuum within the chamber aids the vaporization of the solution and the absence of air helps H2O2 molecules to go everywhere. Some sterilizer cycles also include the use of plasma or ozone as a means of further reducing H2O2 residuals and/orto enhance the cycle lethality. A vacuum is applied again to remove the sterilant from the sterilization chamber. The previous steps are repeated to provide a sterilization process with an appropriate safety margin. Finally, the chamber is evacuated and filled with air for the sterilized load to be safely retrieved. Note that the evacuated H2O2 is broken down into oxygen and water vapor by a catalyst before being released safely into the room. Despite the heat used to vaporize the hydrogen peroxide solution, the process remains at relatively low temperatures (<55°C or <131°F), making it suitable for heat sensitive devices that would otherwise be damaged by steam sterilization. Contrary to liquid H2O2 disinfection, vaporized H2O2 sterilization achieves Sterility Assurance Level (SAL) and leads to packaged devices that remain sterile until use. We’ll talk about SAL in our next installment.