We started developing cycles using pure solutions with different H2O2 concentrations (from 8% up to 16%) in order to find the right balance between efficiency, cycle times and consumption. We had a clear idea that 35% was definitively too much for our methodology due to risks associated with corrosion. We reached the conclusion that 12% offered the best yield for regular environmental conditions found in most laboratories and cleanrooms; between 18-27°C temperature and 40-70% RH. In addition, we were requested to avoid the use of blends with PAA or others (e.g. Silver cations, etc) because pharma industry does not like to have residual traces of compounds, because of the higher corrosion properties of PAA and also because of safety health concerns.  

The quantity of biocide is directly related to the overall volume of the room or enclosure. We have carried out multiple tests to check the efficacy on different environmental conditions and we have a deep knowledge on how to reach different decontamination levels accordingly. We have established a common rule, providing the right quantity of biocide to be used for the volume to be decontaminated based on the challenge we want to achieve (log 4, log 6). Anyway, when developing a cycle, beside the environmental factor, it is necessary to consider the architecture of the area, the situation of furniture or machinery, barriers, etc. All this can influence the quantity of biocide to be injected.

This question cannot be answered without defining the case. The cycle time is divided in 3 phases: injection phase, contact phase and aeration phase. The most difficult one to be defined is the aeration because it is related to different factors that are beyond our control. The most important one is the Air Handling matter; i.e. the capacity to renew the air with new fresh air and the air flow capacity or air changes per hour. If the system is not able to renovate its air completely (e.g. only 30% of air circulation is fresh air), the decrease of H2O2 concentration will take longer.  Same if the air changes per hour are lower. On the other hand, the injection time and the contact time are more easily defined but they are not the longest part. Our equipment is designed for injection rates between 10 to 25 ml/min. This means that if we need to inject 2 litters at a rate of 20 ml/min, the injection time will take approx. 1h and 40 min. Then, the contact time is to be defined during cycle development but is should be typically between 30 min to a maximum of 2 hours, depending on the volume. However, these values can also be influenced by the environmental conditions and of course by our target as far as the decontamination or log-reduction required.

Concerning cleanrooms, there’s not a maximum volume because we define the number of units (VH2O2 generators or injection points) depending on this. Moreover, the position and number of the injection points is also related to the layout or architecture of the area, the design of the HVAC system, etc.

The methodology of Solidfog is based in inject the right quantity of biocide to get close to the dew point. At this moment, micro-condensation starts occurring. This is also influenced by the initial temperature and relative humidity in the room and enclosure. We have determined a quantity to be injected based on the area's volume, we will then inject it at a certain flow rate. Based on those 2 data (volume to inject and flow rate) we will have a theoretical injection time, contact time will then start right after end of injection.

The level of ppms or concentration of H2O2 in the cleanroom or enclosure is one measure that do not determine by itself only the sporicidal effect achieved. It has been demonstrated that the sporicidal effect is also related to the level of humidity in the ambient*. In other words, a cycle developed in such a way that the concentration achieved at 53% RH is 400 ppms can have the same D-value effect than another one in which the concentration achieved is 800 ppm at 25% RH. At the end of the day, these parameters are linked because the higher is the humidity (H2O in gas phase), the less space is available for H2O2 in gas phase. Since our methodology does not require to decrease the humidity of the environment, we take advantage of this phenomenon and we do not require to have such high concentrations of H2O2 in the environment.   

*"The Influence of Humidity, Hydrogen Peroxide Concentration, and Condensation on the Inactivation of Geobacillus stearothermophilus Spores with Hydrogen Peroxide Vapor". Beatriz Unger-Bimczok & Volker Kottke & Christian Hertel & Johannes Rauschnabel J Pharm Innov (2008) 3:123–133 DOI 10.1007/s12247-008-9027-1. Published online: 8 May 2008 # International Society for Pharmaceutical Engineering 2008.  

Yes, the compressed air is mixed with the biocide. The 2 fluids (compressed air and H2O2) meet in the atomizer which then allows the fragmentation of the liquid into microdroplets. These are then dispersed in the volume thanks to the energy provided by the compressed air. These microdroplets then have a relatively short duration and pass into the gas phase.

We performed several tests and these showed a typical spray pattern ranging from very small sizes (less than 5 μm) to 20 μm. According to our understanding and because of the technology we use, droplet life or evaporation time is as critical as the droplet diameter. The small droplets evaporate easily, but it is the large droplets that can reach greater distances during their evaporation. Therefore, having a good rational droplet size will allow a good dispersion while having a good rate of evaporation. This also makes it possible to avoid the use of fans to dispense the biocide.


The value is of course set by the public safety authority (usually less than 1 ppm in the EU, to be checked on a case-by-case basis). The rincing of the air (aeration phase) depends on the air treatment of the room; work with 100% fresh air and 30-40 ACH (air change per hour) is better than 50% fresh air and only 20 ACH. Then, the location of the blow and suction zone is important. The most usual aeration time according to the typical characteristics of a clean room is 2 to 3 hours. A NeutraMist® catalytic system can also be used to reduce this aeration time and reach the 1 ppm threshold faster.

It is true that the chemical indicators do not always give a precise idea of the disinfection carried out. Some indicators offer a good estimate of the cycles executed - better reliability - while others are very poor. We recommend the use of a certain type of chemical sensor with a reading that is sufficiently correlated with the results of biological reductions that can be expected.

Yes, it is possible to use a higher concentration but with a higher risk of corrosion if used in a room with an initial relative humidity greater than 60%; in practice, for very short cycles on small volumes, a higher concentration choice may be useful. We usually ask to be notified of this type of change to confirm compliance of the equipment with the selected biocide.

Standard delivery time is 10 to 14 weeks, but it will depend on the number of units and also their degree of customisation. We are flexible and this aspect can always be discussed.