Humidity, condensation point, and maximum achievable vH2O2

Humidity effect on condensation in vaporized hydrogen peroxide bio-decontamination
Joni Partanen
Product Manager
Published: Oct 26, 2021
Life Science

This blog is the first in a 4-part series where we describe how process parameters influence condensation and the maximum achievable concentration of hydrogen peroxide vapor during vH2O2 bio-decontamination applications. 

In this series we propose four basic process parameter rules.  But before we address the first parameter that affects condensation and the maximum achievable vH2Oppm, we will review two important values: relative humidity and relative saturation.   

Because water (H2O) and hydrogen peroxide (H2O2) have similar molecular structures, both affect the condensation point of the air. However, relative humidity (RH) indicates only the level of water vapor in the air at a given temperature, whereas relative saturation indicates the level of water vapor as well as hydrogen peroxide vapor in the air.  In air that contains hydrogen peroxide vapor, condensation will occur before 100% relative humidity. Therefore, the condensation point can reliably be anticipated with the relative saturation (RS) measurement. 

When relative saturation reaches 100 %RS, the vapor mixture will condense. Relative humidity and relative saturation differ whenever there is vH2O2 present and the difference between RH and RS is further affected by the amount of vH2O2 present.  Once condensation occurs (relative saturation has reached 100% RS), the ppm vH2O2 can no longer increase. In fact, H2O2 vapor concentration will often decrease as some vH2O2 will decompose into water and oxygen upon condensation. When this occurs, more vH2O2 must be injected to compensate. 

If there is dripping condensation by the end of the decontamination phase, vH2O2 ppm readings may initially increase during aeration because the droplets release vH2O2 back into the air.

This brings us to the first rule:  Lowering the initial level of humidity increases the amount of H2O2 vapor that can be used before condensation.  

The graphs below illustrate that when relative humidity is higher at the onset of the conditioning phase (because de-humidification was not performed), condensation occurs sooner during decontamination. Therefore, the lower the relative humidity when conditioning begins, the higher the maximum achievable ppm vH2O2 before condensation occurs.  

During the decontamination phase, some vH2O2 will decompose into water and oxygen. The amount of vH2O2 that decomposes will depend on conditions such as: materials, temperature, humidity, and air flow. The actual decomposition expected under certain conditions must be measured.  In following graphs, we have assumed that 10% of vH2O2 has decomposed from its initial value and more H2O2 is vaporized to compensate.        

Relative Humidity in VHP bio-decontamination processes


Relative Humidity in VHP bio-decontamination processes Concentration Solution 59%-m

As shown, dehumidification prior to conditioning influences the maximum achievable ppm vH2O2. In figures 1a and 1b, the hydrogen peroxide solution used is 12%-m; figures 1c and 1d use a concentration solution of 59%-m. Figures 1a and 1b show two otherwise similar bio-decontamination cycles; orange lines indicate processes without dehumidification and a conditioning phase that begins with relative humidity at 50 %RH. The blue lines show processes where dehumidification was completed to 10 %RH prior to the conditioning phase.

Figure 1a and 1c show the effect of dehumidification on humidity percentage - indicated by relative humidity and relative saturation - during conditioning and dwell phases. Figure 1b and 1d show the effect of dehumidification on the maximum achievable hydrogen peroxide vapor during conditioning and dwell phases.

In our second blog in this series, we will illustrate how the H2O2 solution affects the amount of H2O2 vapor that can be used before condensation occurs. 
To read the complete white paper upon which these blogs are based, visit this web page: “Considering Condensation: Influences in Hydrogen Peroxide Vapor Bio-decontamination” 


Jaime lopez ochoa

Dec 1, 2021
I need catalog


Dec 3, 2021
Dear Jaime, You will find the Vaisala catalog here:

Rolando Martell Aedo

Dec 8, 2021
he relative saturation point in a clean room varies from site to site within the premises. In the qualification I must monitor the reach of this saturation point after the nebulization or conditioning stage (time and contact), at each site where I sample with the bioindicator. In other words, I must use several probes in the measurement according to sampling stations with bioindicator. To correlate.

Sanna Lehtinen

Dec 21, 2021
Dear Rolando, Yes, you are absolutely correct that temperature, as well as Relative Saturation and Relative Humidity, may vary within the site. If we want to avoid condensation during vH2O2 bio-decontamination process in an environment with temperature differences, we have to know what is the lowest temperature. If we do not know that, we recommend measuring mixture dewpoint Td with the HPP272 probe and measuring the temperature at different locations with additional temperature sensors. If measured temperature equals to or is lower than mixture dewpoint, then there might be condensation.

Bruno Aze

Jan 6, 2022
Hi ,
do you have any data on measurement acquisition time of your sensor ?

Joni Partanen

Jan 19, 2022
Hi Bruno,
HPP270 products have a response time of the 70s (τ63%), meaning that if there is a step-change in the H2O2 concentration, let’s say from 0 ppm to 500 ppm, the reading will be 63% of the final reading (~315 ppm) after 70 seconds and 90% of the final reading (450 ppm) in 200 seconds.
Best regards, Joni

Naci Sivri

Jan 25, 2022
Dear Joni,
Thanks for your work. We use your HPP270 sensors happily in our production. We have different values for min vppm levels for room biodecontainment. Which ppm level do you advice for BSL-3 Labs?

Joni Partanen

Feb 16, 2022
Dear Naci,

Our expertise in bio-decontamination is in the measurement of vaporized hydrogen peroxide concentration and relative saturation. These parameters will enable accurate and reproducible process control. However, determination or recommendation of the suitable concentration and exposure time requires microbiological expertise and empirical testing in the actual application. This is unfortunately beyond our competence.

Best regards, Joni

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