Expert advice on hydrogen peroxide vapor sensing

In case you missed our recent webinar "Achieving Effective H2O2 Bio-decontamination in Facilities & Containment Systems" you can watch the recorded version.

During the webinar we received many questions we did not have time to answer. Our experts answered afterwards and here we share their advice on questions that are broadly under these three categories:

• Vaporized Hydrogen Peroxide Sensors
• Equipment, Materials and Structures
• Biological Indicators

Vaporized Hydrogen Peroxide Sensors

QUESTION: When we use a typical RH sensor in the cycle development, do they measure Relative Humidity or Relative Saturation? In other words, does vaporized H₂O₂ affect the RH reading of typical RH sensors?

ANSWER: Water and hydrogen peroxide have a very similar molecular structure, and they both affect the humidity of the air, in which they are present. Therefore, a typical RH sensor without catalytic layer will have a greater humidity value than real saturation level of the air mixture is. So yes, the vaporized H₂O₂ does effect the typical humidity sensor and it will cause accelerated drift in the sensor with repeated exposure. The relative humidity sensor with a catalytic layer measures the humidity of the air caused only by water vapor. During H₂O₂ exposure the RH% value is lower than relative saturation RS% value. Learn more about relative saturation in this webinar.

Also, Vaisala offers some of our traditional RH/Temperature instruments with sensors that include a catalytic layer. This layer, along with our warmed probe technology and chemical purge features, can offer a real RH measurement with vaporized H₂O₂ present. Information on these other instruments:

Humidity and Temperature Probe HMP3

Humidity and Temperature Meter Series HMT330

Hydrogen Peroxide HPP270

Equipment, Materials and Structures

QUESTION:  Is vaporized H₂O₂ recommended over a fogging system?

ANSWER: The HPP270 series probes can be used to measure vaporized H₂O₂ in both cases.There are several variables to consider when choosing a system for bio-decontamination. Vaisala does not take a position on vaporizer or fogging systems. We provide sensing equipment for intelligent monitoring and control of critical processes. It’s best to speak with a system vendor to learn if the equipment will meet the needs of your applications.

QUESTION:  What equipment and MOC's (maintenance in operational condition) are generally used for H₂O₂ decontamination, including room construction, HVAC systems (including ducting seals)? I've seen the need for powered seals to block the return and supply ducts in a fermentation room because the air handler was not only connected to this room, but was at risk of returning vaporized hydrogen peroxide to other areas with occupants.

ANSWER: We recommend reviewing the resource materials we provided during the webinar for reference. That said, materials that can survive the corrosive effects that H₂O₂ condensation are needed.

QUESTION:  Could you comment on reports that vaporized H₂O₂ is absorbed by materials in the room or isolator then leaches out over time after aeration? This leaching effect could result in accumulation in under ventilated areas or inactivation of the product being manufacturing in the H₂O₂ fumigated facilities?

ANSWER: Thank you for the question, and while Vaisala is not in a position to comment of the results of vaporized H₂O₂ desorption may have, we do know that certain materials will absorb and release vaporized H₂O₂ at different rates and concentrations. Careful material selection for areas and items in the process, combined with sufficient aeration duration times can help to mitigate any potential latent effects. Proper cycle development for problem areas can include a post-aeration phase that might involve additional low level monitoring.

QUESTION:  In a laboratory that is decontaminated twice a year and the H₂O₂ is extracted via metal ductwork, what is the likelihood of the ductwork corroding over time?

ANSWER: There are too many variables to consider to provide a confident answer. The safe answer is to say that regular inspections should be performed if there is any danger of corroded ductwork to expose different areas to unsafe levels of the vaporized H₂O₂ being extracted.

Factors that would influence the likelihood of corrosion would be the concentration of vaporized H2O2 used in the process, any condensation occurring during the bio-decontamination cycle, or a risk of condensation in the ductwork of the laboratory. If the temperature of the exhaust duct is lower than the air being evacuated, there is a higher condensation and corrosion risk.

QUESTION:  Which is a better method of decontamination: Through Air Handling Unit or direct injection to the room?

ANSWER: It may be easier to use a vapor generator inside the room if there is only one room to be bio-decontaminated. Most of our customers use heat vaporization from a location integrated into the room or isolator. These vapor generators are easily controlled and the temperature differences are more easily managed.

Biological Indicators

QUESTION:  How do we select the location(s) for biological indicators for a bio-decontamination challenge study?

ANSWER: Although Vaisala does not sell biological indicators, we have seen that many of our customers put BIs in places they think will be most difficult to bio-decontaminate. A vendor of biological indicators can provide product specifications and guidance. However, there are people in sterilization services who offer their experience in blogs and other publications. Here is a blog from one service provider, Ardien Consulting. “The Rogue Biological Indicator.”

QUESTION:  Do you recommend placing Biological Indicators in triplicate to prevent "rogue" BIs? And would you suggest running BI's in duplicate or triplicate (in one location)?

ANSWER: Thank you for the question, but Vaisala is not in a position to provide guidance for products and methods that we are not directly involved with. I recommend reviewing the resource materials we provided with the webinar for reference. That said, we know that is commonplace to use duplicate BI’s to increase the assurance level, and triplicate BI’s can be used in more challenging areas.

Here are some reference materials available from various industry organizations, some are for purchase:

• "Resistance of Common Spores of the Genus Bacillus to Vapour Hydrogen Peroxide" M. Kokubo, T. Inoue, and J. Akers, PDA Journal of Pharmaceutical Science and Technology, Vol 52, No. 5 

• "Development and Quantification of H₂O₂ Decontamination Cycles" Volker Sigworth, Claude Moirandat, PDA Journal of Pharmaceutical Science and Technology, Vol 54, No. 4

• "Recommendation on Isolators Used For Aseptic Processing And Sterility Testing"  2002 Pharmaceutical Inspection Co-Operation Scheme

• ISO 11138-1 Sterilisation of Health Care Products - Biological Indicators - Part 1: General Requirements