The Agony & The Ecstasy (of Humidity Sensors with Vaporized Hydrogen Peroxide)

James Tennermann
Nov 8, 2013
Industrial Measurements
Life Science

For this week's blog, we look at vaporized hydrogen peroxide used to decontaminate or sterilize rooms and equipment.

Hydrogen peroxide has the advantage of being an effective biodecontaminant at normal temperatures. This makes it excellent for biodecontamination applications because the gas won't damage temperature-sensitive equipment that cannot be heat sterilized. In addition, H2O2 is a powerful oxidizer and ultimately degrades into water and oxygen without harmful by products.

There are few items important to remember in terms of sensing and measuring H2O2. First, the introduction of hydrogen peroxide into a normal environment has a big effect on relative humidity. The saturation vapor pressure of the mixture is reduced and condensation may occur as the concentration of H2O2 increases. Second, if you are measuring relative humidity in an environment with vaporized H2O2, the humidity sensor is vulnerable to damage. Third, with humidity measurements made in an application that uses H2O2, the trick is to ensure the humidity sensor responds to the properties of the gas mixture, rather than simply measuring the water vapor component of the air.

Vaisala's PEROXCAP sensor uses probe warming technology to ensure that condensation doesn't affect the accuracy of any measurements.

For sensors permanently installed in a space, but not used during the decontamination cycle, the sensor is easily protected with a catalytic filter. The catalyst hastens the breakdown process of the vaporized hydrogen peroxide assuring that the sensor is never exposed. With the catalytic filter, the sensor will measure humidity as if there were no H2O2 in the air mixture, and of course it will always measure normally when there is no H2O2 at all.

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