H2O2 Absorption, Catalytic Layers on Sensors, Vapor Injection Rates and more…

Vaporized Hydrogen Peroxide sensor
Life Science

Questions & Answers from our Recent Webinar on Hydrogen Peroxide Bio-decontamination

 If you were unable to attend this webinar, you can watch it any time. Here are the answers to questions we were unable to get to during the webinar.
 

Quick Survey - How do YOU Measure Hydrogen Peroxide?

Please answer these 4 questions on the technology you currently use and what sort of ppm concentrations you measure.
 

Webinar Questions & Answers:


Question:
Do you have solution for testing H2O2 absorbed in the material?


Answer:

While we were developing the  HPP270 series (HPP271 and HPP272) probes, we tested several materials to select only probe materials that do not absorb or decompose H2O2. The HPP271 and HPP272 probes are for high-level and process-level measurement and therefore not made for testing H2O2 that may be absorbed in the customer's materials (out-gassing studies). 

Question:
Can you explain how pressure and temperature vary during a bio-decontamination cycle? 

Answer:

On the slide presentation, please refer to slide 13, which shows a typical non-condensing bio-decontamination process in an isolator.
vaporized hydrogen peroxide biodecontamination
 
Temperature tends to increase during the dehumidification phase if you use hot and dry air to decrease the humidity. Also, during the conditioning and bio-decontamination phases, temperature increases as warmed hydrogen peroxide vapor is injected into the chamber. Pressure is maintained at the same level during the bio-decontamination phases, but is typically slightly higher than in the surrounding areas of an isolator.

Question: Why is it that other RH sensors without a catalytic layer show much higher values? These sensors are the same as your sensor without a catalyst layer, no? 


Answer:

The PEROXCAP sensors are warmed, which prevents condensation from forming on the sensor. This provides reliable measurement even in condensing conditions. In addition, sensors include a chemical purge function that helps maintain accuracy in challenging H2O2 environments. The purging process involves rapid heating of the sensor to remove possible contamination. The HPP272 probe provides two different humidity values: Relative Humidity (RH) and Relative Saturation (RS).

Relative Humidity is a direct measurement from the catalytic version of the HUMICAP. However, Relative Saturation is a calculated parameter from Relative Humidity, H2O2 and Temperature. To our best knowledge, no other hydrogen peroxide sensor manufacturer has this kind of repeatable and reliable parameter that indicates the actual condensation level of an air mixture that includes hydrogen peroxide vapor. 

Question:
How are Relative Saturation and Relative Humidity linked to the saturation of ppm level during vaporizing H2O2 (35%) in a contained area?


Answer:

You can use different H2O2 liquids to generate H2O2 vapor, for example by using a hot plate. The higher the H2O2 concentration of the liquid hydrogen peroxide, the less water vapor. Therefore, you are able to inject more H2O2 into a chamber before condensation. The generated hydrogen peroxide vapor ppm level and temperature then influences humidity level.

We refer you to the presentation slides, 30 through 43. These slides show how different temperatures and H2O2 vapor concentrations affect different humidity levels (Relative Humidity and Relative Saturation).  
vaporized hydrogen peroxide concentration by temperature graph
 
See presentation. – slide 30 – 43. This graph shows RH% values in different H2O2 ppm concentration and temperature values.

Question:
Can you explain more about the materials used in the Vaisala hydrogen peroxide sensors? Referring here to slide 50? 

Answer:

Different manufacturers' sensors contain different materials. As we learned today in our webinar, the selection of materials proximal to sensing elements is tremendously important to achieve accurate and repeatable measurements. During our Research & Development phase, Vaisala heavily tested all materials used in our measurement probes HPP271 and HPP272. Only materials that do not absorb or decompose H2O2 vapor were selected, such as stainless steel and Teflon.

This is crucial from the standpoint of the user; especially if isolators or rooms to be bio-decontaminated contain many materials that absorb, desorb or decompose H2O2 vapor. If that’s the case, achieving stable H2O2 vapor conditions is challenging and the aeration phase might be prolonged because of the out-gassing phenomenon.  

Question:
Why do the humidity sensors include a catalytic filter?   


Answer:

According to the definition, relative humidity is a measure of water vapor. The function of the HPP270 probe’s catalytic layer is to decompose H2O2 into water and oxygen. Therefore only water vapor reaches the humidity sensor beneath the catalytic layer.

Vaporized hydrogen peroxide is an extremely harsh chemical that causes corrosion to many materials, especially if the process includes condensation. That’s why several hydrogen peroxide sensor manufacturers have included a catalytic filter or layer in their humidity sensors to protect the sensing element. Once H2O2 is catalyzed, the sensor indicates the humidity only caused by water vapor pressure. Humidity sensors without catalytic filter drift quickly in environments with H2O2 vapor, and therefore don’t provide reliable measurement results. 

Question:
I am currently using hydrogen peroxide measurement for monitoring purposes only. Do you know if people commonly use hydrogen peroxide measurement for controlling the hydrogen peroxide injection rate?   


Answer:

Today the majority of users are using H2O2 ppm value for monitoring purposes only. However, you can use reliable and repeatable measurement for controlling the H2O2 injection rate so that the H2O2 ppm level is kept stable during bio-decontamination phase.

In addition, the Relative Saturation measurement can be used to control and avoid condensation if needed. There are already companies that use measured H2O2 ppm value to control H2O2 injection rate during bio-decontamination. We have seen that companies are increasingly using H2O2 vapor concentration and the Relative Saturation value for controlling purposes. 

Question:
I need to monitor humidity all the time - not only during bio-decontamination process. Can I use a Vaisala HPP probe for measuring humidity between bio-decontamination cycles?   


Answer:

The HPP272 probe is a good choice for humidity measurement during bio-decontamination, but also during routine production processes. The HPP272 Relative Saturation value shows you when the air mixture starts to condense during a bio-decontamination phase. When there is no H2O2, % RS is equal to % RH. This means that during normal production processes you could use either the RH or RS parameter for humidity measurement and control.

The HPP272 probe is specifically designed to be used in highly condensing H2O2 environments. Therefore, it provides reliable and repeatable measurement data (RS, RH, H2O2 ppm and T) not only during bio-decontamination but also during production processes. 
 

H2O2

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