Questions
We initially developed our decontamination cycles using pure hydrogen peroxide solutions with concentrations ranging from 8% to 16%, aiming to find the optimal balance between efficacy, cycle time, and biocide consumption.
It quickly became evident that using 35% H₂O₂ was unsuitable for our methodology due to the increased corrosion risks associated with higher concentrations.
Through testing, we determined that a 12% H₂O₂ solution provides the best overall performance under typical environmental conditions found in most laboratories and cleanrooms — specifically temperatures between 18–27°C and relative humidity levels between 40–70%.
Additionally, we were advised to avoid blends containing Peracetic Acid (PAA) or other additives such as silver ions, as these formulations can leave residual compounds, present higher corrosion potential, and raise health and safety concerns.
The required quantity of biocide depends primarily on the total volume of the room or enclosure.
Through extensive testing under various environmental conditions, we have developed a precise understanding of how to achieve different decontamination levels (e.g. log-4 or log-6 reduction).
As a general rule, the biocide dose is determined according to the volume to be treated and the target level of decontamination.
However, during cycle development, additional factors must be taken into account — including the room architecture, layout of furniture or equipment, and the presence of barriers or complex geometries — all of which can influence the amount of biocide required for optimal distribution and efficacy.
There is no universal answer — the cycle duration depends on the specific case and environmental conditions.
A typical VH₂O₂ decontamination cycle is divided into three phases:
Injection phase – vaporization and distribution of the biocide.
Contact phase – exposure time to achieve the desired microbial reduction.
Aeration phase – removal of residual H₂O₂ to return to safe operating conditions.
Among these, the aeration phase is usually the most variable, as it depends on factors beyond our control, particularly the air handling system (HVAC).
Key parameters include the fresh air renewal rate and the number of air changes per hour (ACH).
If the system only renews part of the air (for example, 30% fresh air), the H₂O₂ concentration will decrease more slowly.
Similarly, a lower ACH extends the aeration time.
By contrast, the injection and contact phases are easier to define.
Solidfog systems operate with injection rates between 10 and 25 mL/min.
For example, injecting 2 litres at 20 mL/min takes approximately 1 hour and 40 minutes.
The contact phase is determined during cycle development, typically lasting 30 minutes to 2 hours, depending on the treated volume and the target log reduction.
Environmental factors (temperature, humidity, and airflow) can also influence the total duration, which must be optimized for each specific application.
For cleanrooms, there is no fixed maximum volume.
The treatment capacity depends on the number of VH₂O₂ generators or injection points used, which are defined according to the room size, layout, and HVAC design.
The positioning and quantity of injection points are therefore adjusted to ensure uniform biocide distribution and effective decontamination, regardless of the total volume.
Solidfog’s methodology is based on injecting the exact quantity of biocide required to approach the dew point, at which micro-condensation begins to form.
This phenomenon is influenced by the initial temperature and relative humidity within the room or enclosure.
For each area, we calculate the biocide quantity to be injected according to its volume, and deliver it at a defined flow rate.
From these two parameters — injected volume and flow rate — we can determine the theoretical injection time.
The contact phase officially begins immediately after the end of the injection phase, when the required vapor concentration and micro-condensation conditions are reached.
The H₂O₂ concentration in ppm inside the cleanroom or enclosure does not alone determine the sporicidal effect achieved.
Studies have shown that relative humidity (RH) plays a significant role in the overall biocidal performance of vaporized hydrogen peroxide.
In other words, a cycle reaching 400 ppm at 53% RH can achieve the same D-value reduction as another reaching 800 ppm at 25% RH. These parameters are interdependent: the higher the humidity, the less gaseous space is available for H₂O₂ molecules, since both water vapor and peroxide occupy the same gas phase.
Because our methodology does not require humidity reduction prior to injection, Solidfog takes advantage of this physical balance — achieving effective sporicidal activity at lower H₂O₂ concentrations, while preserving material compatibility and process safety.
Reference: “The Influence of Humidity, Hydrogen Peroxide Concentration, and Condensation on the Inactivation of Geobacillus stearothermophilus Spores with Hydrogen Peroxide Vapor,” Beatriz Unger-Bimczok et al., Journal of Pharmaceutical Innovation (2008) 3:123–133, DOI: 10.1007/s12247-008-9027-1.
Yes. The compressed air is mixed with the H₂O₂ solution inside the atomizer, where both fluids meet.
This interaction causes the liquid to break into fine microdroplets, which are then dispersed throughout the volume by the energy of the compressed air. These microdroplets quickly evaporate, transitioning into the gaseous phase to achieve uniform vapor distribution and effective decontamination.
Our tests have shown a typical spray pattern with droplet sizes ranging from below 5 μm up to around 20 μm.
In our technology, both the droplet diameter and the evaporation time (droplet lifetime) are critical parameters.
Smaller droplets evaporate rapidly, while larger ones travel farther before evaporation, enhancing the overall distribution of the biocide. Achieving an optimal balance in droplet size ensures homogeneous dispersion and an efficient evaporation rate, making it possible to avoid the use of additional fans or air mixers during diffusion.
The Threshold Limit Value (TLV) for hydrogen peroxide is defined by public safety authorities and typically set at below 1 ppm in the European Union (to be confirmed according to local regulations).
The aeration or rinsing phase duration depends largely on the room’s air handling system.
Rooms supplied with 100 % fresh air and achieving 30–40 air changes per hour (ACH) will reach safe concentrations significantly faster than those operating with 50 % fresh air and only 20 ACH.
The location of air inlets and extraction points also influences the overall aeration efficiency.
Under typical cleanroom conditions, the aeration phase generally lasts 2 to 3 hours to reduce the H₂O₂ concentration below the 1 ppm threshold. When equipped with a NeutraMist® catalytic system, this aeration time can be considerably shortened, allowing a faster and safer return to operational conditions.
Chemical indicators (CI) do not always give a fully accurate representation of the disinfection level achieved.
Some indicator types offer a reliable correlation with the actual biological reduction, while others provide only a rough estimate of cycle performance.
At Solidfog, we recommend using validated chemical sensors whose readings are closely correlated with biological indicator results, ensuring a more dependable assessment of decontamination efficiency.
Yes, it is technically possible to use a higher H₂O₂ concentration, but this involves an increased risk of corrosion, especially when the initial relative humidity exceeds 60%.
In practice, using a higher concentration may be acceptable for very short cycles or small-volume applications.
However, Solidfog should always be informed before any change in biocide concentration, so that we can verify the equipment’s compatibility and ensure continued process safety and compliance.
The standard delivery time is typically 10 to 14 weeks, depending on the number of units ordered and the level of customisation required. We remain flexible, and delivery schedules can always be discussed and adapted to meet project needs.