Did you know that ozone can be used to sterilize heat- and moisture-sensitive medical devices? Ozone, also known as trioxygen, is an inorganic molecule with the chemical formula O3. It is a pale blue gas, with an unpleasant, distinctive smell similar to chlorine. In fact its name derives from the Greek word ozein, which is the verb “to smell.”

 

In the earth’s stratosphere, ozone exists in high concentrations and acts as a shield that absorbs most of the sun’s ultraviolet radiation, hence the term “ozone layer.” But as a sterilizing agent, ozone has a very different role.

View of the inside of a pressure cooker - Tuttnauer - Sterilization Basics

In the stratosphere, ozone acts as a shield that absorbs most of the sun’s ultraviolet radiation

Long used for the disinfection of drinking water, ozone is now getting more attention for its strong oxidizing properties. Tim Stoddard, CEO of Cylopss and a pioneer in the world of ozone sterilization, explains how ozone works:

“Ozone is a unique antimicrobial agent. In fact, it is the most aggressive oxidating (sic) antimicrobial agent known to man. Ozone is formed by applying electrical energy to the oxygen molecule, which splits some portion of those oxygen molecules in half, into singlets of O. Those single O atoms attach to O2 for a very short time period, becoming O3, which has a half-life in its natural state of about 20 minutes before, on its own, it converts back to oxygen by releasing its singlet of O. During that active phase as ozone, it reacts to any organic compound by oxidizing double carbon bonds. So, unlike a lot of other disinfection sterilization technologies, in the act of literally taking a cell membrane apart, in destroying the cell, it converts itself back to oxygen which is a very benign waste product. If you look at water that has been disinfected with a chlorinated compound versus ozone, you’ll see dead microorganisms in the chlorinated water. If the water has been treated correctly with ozone you should literally see nothing because it should break it down to just its basic elements which are hydrogen and CO2."

How Ozone Sterilization Works

An ozone sterilizer is able to harness the unique powers of ozone by producing it inside the sterilizer from medical grade oxygen, which is commonly available in hospitals (as explained above, by applying electrical energy to combine O2 with O to form O3). This capability is well-suited for sterilizing delicate medical devices, like endoscopes, that cannot withstand the high heat and humidity of standard steam autoclaving. Approved by the FDA in 2003 as a new sterilization process for low-temperature sterilization, its microbial efficacy has been proven with a variety of microorganisms, including the most resistant Geobacillus stearothermophilus, (which is often the bacterium of choice for biological indicators).

Actually, on its own, ozone can be quite dangerous: it is toxic, corrosive and flammable, but since the ozone is produced and broken down within the sterilizer, chances of exposure to it are quite minimal. The waste ozone is destroyed by passing through a simple catalyst, which brings it back to a state of oxygen that can be safely expelled into the air.

Advantages Disadvantages
Needs only medical grade oxygen, which is not a dangerous gas to handle or transport Ozone itself is a toxic and flammable gas
Medical-grade oxygen is readily available in hospitals all over the world, removing the additional overhead of stocking expensive sterilant Cycle time is longer than hydrogen peroxide plasma sterilization
Does not leave toxic fumes or residue that must be aerated; rather converts back to oxygen that can be safely released into the air  
If there were to ever be a leak, even very tiny amounts of ozone could be detected from its pungent smell  
Cycle time is shorter than EtO sterilization  
Cost per cycle is cheaper than EtO since oxygen is cheaper to acquire than EtO  

 

How Popular Is Ozone Sterilization?

 

In low-temperature sterilization, as we have posted on our blog, there are several options. The most popular remain Ethylene Oxide (EtO), Formaldehyde, and Hydrogen Peroxide Plasma. Today, however, with the health risks associated with formaldehyde becoming more and more worrisome, many hospitals and sterilization departments are phasing out these options. Hydrogen peroxide plasma remains popular, and we are seeing an increased interest in ozone sterilization as a safe and cost-effective alternative. Another type of low-temperature sterilization method gaining attention is nitrogen dioxide sterilization.

Optimistic about Ozone

Ozone has exciting potential as a sterilizing agent in the world of low-temperature sterilization. After all, it has been used for many years to disinfect drinking water, food, and air. Now that the infection control industry has figured out how to maximize its germicidal properties inside a sterilizer, we expect to see more ozone sterilizers in hospital CSSD/SPD rooms. It’s relatively safe and its cost-effectivity will ultimately prove to be a selling point over the more dangerous alternatives, such as formaldehyde. And in some ozone sterilizers it is already being paired with hydrogen peroxide plasma in order to perform a double-fronted assault on microorganisms. One thing is for sure: we will be hearing more in the coming years about ozone as a viable alternative for low-temperature sterilization.