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It is important to identify the different hydrogen peroxide systems that are in use today, the different abbreviations associated with each and to highlight the differences between them.

VHP refers to vaporised hydrogen peroxide and is a trademark of Steris who were one of the original pioneers in hydrogen peroxide technology. This decontamination process is reliant on a high vapour phase concentration which is achieved by initial dehumidification of the air. The process uses 30-35% hydrogen peroxide liquid which is flash evaporated to achieve the required vapour phase concentration. The process is always stopped before the dew point is reached and for this reason is often referred to as a “Dry” process.

HPV refers to hydrogen peroxide vapour and is a term that is used by Bioquell. Similar to Steris, the process flash evaporates 30-35% hydrogen peroxide to create a vapour. However, there is no initial dehumidification and the process is brought beyond the dew point to saturated vapour conditions. The process relies on the formation of micro-condensation on surfaces and for this reason is often referred to as a “Wet” process. The physical chemistry and partial pressures of a saturated hydrogen peroxide vapour means that when condensation is formed, it is at a concentration significantly greater than the original 30-35% of the liquid solution. Depending on ambient temperature and humidity, the actual concentration of the condensate will be in the region of 50-60%. This is an important point when it comes to material compatibility and discussed below.

iHP refers to ionized hydrogen peroxide and is a trademark of Steramist, this process uses a 6-10% concentration of hydrogen peroxide. An ultrasonic nozzle creates a dry mist of ionized hydrogen peroxide and it is these negatively charged hydroxyl ions that act as the mechanism for destruction of micro-organisms.

For each process, typical VHP vapour phase concentrations would be in the region of:

VHP 600-800ppm

HPV 200-300ppm

iHP 80-100ppm

The opinion of some in industry is that the “wet” process can cause material damage but the “dry” process has much better material compatibility characteristics. This article does not set out to debate this but the reason for this is likely to be due to the higher concentration of the condensate (50-60%) as mentioned above.

When we consider iHP and the discussion of material compatibility, the important point to note is that the concentrations are significantly lower, both in the liquid and vapour form. On this basis it is a reasonable statement that the iHP process is significantly “gentler” on materials than both VHP and HPV.

While globally there have been a small number of reported cases of 30-35% hydrogen peroxide systems causing damage to surfaces, there has not been a single case of iHP causing any damage whatsoever.

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