I have been working in the development of Solidfog Technologies‘ biodecontamination systems business for more than 7 years. I have witnessed the excellent results achieved with their technology. It is a different and an innovative solution, designed to meet the standards and expectations of the pharmaceutical manufacturing companies. Getting the first projects in Spain was not an easy job. At first, in my presentations, I could notice some disbelief in the audience. There were certain “dogmas” that no one questioned, and this fact prevented the necessary mind openness to understand that other solutions could provide greater advantages. In order to be able to explain myself better, I began to investigate the scientific background and the reasons why of the airborne H2O2 biodecontamination, both vaporized and nebulized. After a few years doing challenge tests and cycle development, I think I have gained enough practical experience to reiterate that, such misconceptions are spoiling the development of projects and/or the optimization of biodecontamination processes.

Faced with this situation, I have been encouraged to write this blog in which I will quote some of the misconceptions or myths that I have heard saying about biodecontamination with H2O2. I will try to explain clearly and concisely why such statements are wrong.

Misconception nº1 – The H2O2 vapor (VHP) has a higher biocidal capacity than dry fog or nebulized H2O2.

This belief comes from the idea that direct vaporization allows to reach high levels of H2O2 concentration in the atmosphere. On the other hand, nebulization is perceived as a less efficient process with distribution in liquid phase. That’s not true. How does the misting that produces dry fog really work? This type of nebulization produces an aerosol or suspension of liquid particles in a gaseous medium. These particles have the ability to move occupying all the available space, but at the same time, because they are so small, they also vaporize. This vaporization occurs until the mixture saturates the environment. Then, no more particles evaporate and begin to be visible as dry fog. Therefore, dry fogging can be seen as a method of cold vaporization, as opposed to direct vaporization, which requires a heat source.

The key question to discern about the biocidal capacity of one method or another is: What is the mechanism that produces the death of microorganisms? If H2O2 is an oxidizing substance that destroys DNA and proteins in cells, what is the best way to distribute the biocide and come into contact with microorganisms? Studies carried out by Beatriz Unger-Bimczok et al (Influence of Humidity Hydrogen Peroxide Concentration and Condensation on the Inactivation of Geobacillus st.) showed that there was a direct relationship between condensation and the lethal effect. Very briefly, they observed that very high sporicidal rates can be achieved with low concentrations (ppm of H2O2) in the environment providing the humidity level was high. These experiments showed that the biodecontamination process is in fact a two-stage process. To achieve decontamination, it must first be vaporized, and second, the vapor must condense. Some referrals such as Tim Coles, in his article Understanding the VH2O2 decontamination process, have called this primary condensation ‘microcondensation’. This occurs when the mixture reaches saturation. In fact, this condensation, which is invisible to the naked eye, is the true cause of the sporicide effect because it is highly concentrated H2O2. In short, if the aim of the process is to decontaminate surfaces and microorganisms are on surfaces, let’s focus on bringing H2O2 to surfaces. This will be better achieved by causing H2O2 microcondensation than by producing a high concentration of H2O2 in gas phase.

In conclusion, the key element in biodecontamination is about how the vapor distribution process is handled and how to ensure that microcondensation occurs on surfaces, and not about the vaporization technology itself and/or about the achieved environmental concentration. The technology that provides a more homogeneous distribution of H2O2, with lower peroxide consumption and in less overall time, will be the one that will offer the greatest advantages and benefits. In this sense, nebulization has enormous potential that is worth exploring.

Misconception nº2 – The dry vapor of H2O2 (VHP) is not corrosive, meanwhile wet vapor and misting are. 

This other statement comes from the misconception that VHP is a gas and this allows a dry process without condensation, avoiding corrosion. But VHP is not a gas, it is a vapor. The VHP generator tries to obtain environmental conditions with low humidity and high concentration. However, even under these environmental conditions, H2O2 and its diluent, H2O, are below their boiling point. Under these conditions, steam does not behave like a perfect gas. In other words, in the environmental conditions existing in clean rooms, vaporized H2O2, whether generated directly by heating or nebulization, can condense even when the relative humidity is much lower than 100%. In reality, H2O2 and H2O do not condense simultaneously due to its different boiling points and/or vapor pressure. A mixture of H2O2 and vaporized H2O will saturate earlier (Relative Saturation) than would happen being only water vapor (Relative Humidity). And it is precisely when reaching 100% relative saturation, that the molecule of greater molecular weight (H2O2) will condense before condensing water (H2O). This primary condensation, called microcondensation, is the real responsible for the sporicidal effect and happens in all biodecontamination processes.

As for corrosion, as described above, whether the process is dry or wet, there will be condensation of H2O2. The question is not to exceed a certain amount of condensation and what level of concentration that condensation entails. Injecting a 35% solution of H2O2 (common in vaporization processes) allows to reach higher environmental concentrations, but also brings a  much more concentrated condensate, which is more corrosive. On the other hand, the solutions commonly used in nebulization, which have a concentration between 8 and 12%, are less aggressive. An excess of condensation, for example, due to a colder area in a room, could be corrosive if we use H2O2 at 35% and much more tolerable if the solution used is 12%. So one thing makes up for the other.

In conclusion, the risk of corrosion, if it would be associated with condensation, can be present in one system or the other and, in any case, its degree of affectation is more related to a poor definition of the process than to the technology used.

To be continued…