Humidity Measurement in Hydrogen Peroxide Sterilization Process in Life Science Industry

Humidity Measurement in Hydrogen Peroxide Sterilization Process in Life Science Industry
/ APPLICATION NOTE
Humidity Measurement in Hydrogen Peroxide
Sterilization Process in Life Science Industry
Built-in value
Maintaining contamination free areas is a must in life science industries
and critical environments are also sterilized regularly. Some of these
areas include small volume chambers like isolators and incubators and
less often larger spaces like cleanrooms and processing lines. Vaporized
hydrogen peroxide (VHP) is an effective agent for decontamination/
sterilization when high enough VHP concentration and long enough
exposure time are applied. Excessively high VHP concentration can
result in unwanted saturation and surfaces wet with liquid hydrogen
peroxide. Humidity measurement in VHP sterilization is an essential
part of the procedure to control the VHP saturation level.
Humidity Influences the
VHP Saturation Level
Humidity levels have a direct
correlation to temperatures at which
the air containing VHP will saturate.
When saturation conditions occur,
condensate, including liquid hydrogen
peroxide, will form on surfaces in
the decontaminated space. The
decontaminated space may be dried
prior the VHP exposure to reach
high enough VHP concentration
without saturation. The change of
gas saturation rate is due to the
molecular structure of hydrogen
peroxide (H2O2) which is similar to
water vapor (H2O).The mixture of these
two gases determines the saturation
vapor pressure of the gas mixture.
Hydrogen peroxide has relatively low
saturation pressure which will increase
the possibility of saturation of the air
containing humidity.
▪
Vaisala HUMICAP® humidity
sensors can measure the VHP
saturation rate directly
(0-100%)
▪
Humidity output can be used
to control the VHP generator
▪
Catalytic filter available for
saturated VHP to protect the
sensor
▪
Vaisala sensor warming to
prevent sensor and filter from
getting wet
▪
Vaisala chemical purge feature
to optimize long term sensor
performance
▪
Reliable measurement
instruments with global
customer support
VHP Compliant Humidity
Measurement Technology
from Vaisala
Vaisala HUMICAP® Humidity
measurement technology with thin film
capacitive polymer sensors is capable
of humidity measurements prior and
during VHP exposure and in high and
low VHP concentrations. The main
advantage of the HUMICAP® sensor
is that it is compatible with VHP even
without any specific protection. In
applications where saturation occurs
a Vaisala protective catalytic filter is
recommended.
Measure VHP Saturation
Level
The ability to measure humidity
directly in mixtures of VHP and air
allows the user to follow the true
saturation level of the gas mixture.
Hydrogen peroxide and water are
both polar molecules that change the
polymer sensor capacitance. Because
may damage materials that are exposed
to these conditions regularly. In this
environment, sensor protection with
a catalytic filter is recommended to
protect the sensor and to extend the
calibration interval.
3. Measure true saturation
of the humid VHP gas
The Vaisala VHP catalytic filter is available
for a wide variety of humidity probes
the Vaisala HUMICAP® directly measures
the true VHP saturation rate (0-100%), it
can be used to control the sterilization
process. Saturation level is highly
valuable information especially when
wet surfaces must be avoided.
Seven Good Reasons to
Choose Vaisala HUMICAP®
for the VHP Application
1. Durability for direct
VHP exposure
The Vaisala HUMICAP® sensor is
compatible with direct VHP exposure
even at high concentrations and
hundreds of VHP cycles up to saturation.
The long term performance is very good
at concentrations higher than typically
used for sterilization. However, for
the applications where full saturation
is possible a Vaisala catalytic filter is
recommended.
2. Catalytic VHP filter for
saturated conditions
When VHP concentrations are high and
condensation is expected, the Vaisala
catalytic filter is used to generate
additional protection for the humidity
sensor. The catalytic filter is based on
the generally known method where
the H2O2 is split to H2O and O2. The
saturating VHP up to wet surfaces
improves the decontamination effect but
The similarity of the water vapor and
vaporized hydrogen peroxide allows
the capacitive HUMICAP® sensor
to read the true saturation rate of a
humid VHP gas. This is important
in VHP applications where the gas
concentration should be high enough to
kill the living organisms, but should not
saturate. This measured value shows
how close the true saturation value is.
If the saturation value is not required
the catalytic VHP filter can be used in
all VHP measurements.
Vaisala HUMICAP® sensors that are
permanently installed to measure
normal operating conditions need
no additional protection beyond the
catalytic filter.
4. Catalytic filter to read plain
humidity in the VHP gas
If the pure humidity in VHP gas is
needed, a normal way is to use a Vaisala
catalytic filter that prevents the VHP
from reaching the humidity sensor,
but allows other gas components to be
measured. When the humidity sensor
is protected from VHP it responds to
humidity only. The influence of the
catalytic filter is about +1 %RH at 300
pmm VHP or +3 %RH at 900 ppm VHP
(at 23°C).
5. Vaisala chemical purge
to complete the long term
stability
The chemical purge technology helps
to correct the possible sensor long
term drift and to extend the required
calibration interval if VHP is measured
without catalytic filter. Chemical purge
automatically heats up the sensor in
set intervals, evaporating the unwanted
excess chemicals out of the sensor
polymer. This returns the sensor
performance back to the same level
as used in normal chemical free air.
For more information, visit
www.vaisala.com or contact
us at [email protected]
By utilizing the chemical purge with the
HUMICAP® sensor the long term stability
for measurement accuracy in VHP
application will be excellent.
6. Vaisala sensor warming to
keep sensor and filter dry in
saturation
Under full saturation conditions, wet
surfaces are not only problematic for
materials, but also for humidity sensors.
The humidity reading will stay at a
100% value until the sensor and filter
have dried. Drying can take a long time
depending on the flow and saturation rate
of the surrounding air. To respond to real
changes in the measured environment
the HUMICAP® sensor is available
with a sensor warming feature. Sensor
warming keeps the sensor surface and
filter temperature higher than the gas
saturation point (dewpoint) and this helps
to avoid saturation on the sensor and
filter. Sensor warming is a proven Vaisala
technology that is used widely when a risk
of a wet sensor must be avoided.
7. Reliable humidity
measurement
The HUMICAP® thin film capacitive
sensor technology was invented and
patented by Vaisala in the early 1970’s.
Since then Vaisala has been leading
the way in humidity measurement
in the most demanding applications.
The latest HUMICAP® 180R humidity
sensor version represents the highest
humidity measurement performance for
complex chemical environments. In VHP
applications it performs with excellent
durability and long term stability. This
excellence combined with the Vaisala
chemical purge and sensor warming
technologies makes the measurement
reliable and the HUMICAP® 180R sensor
uniquely well suited to VHP applications.
Forms of Water and Hydrogen peroxide
molecules
Ref. B21 1205EN-A ©Vaisala 2012
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