BLOG: VHP Resistance and IsoAir® Pro Series Particle Counters

BLOG: VHP Resistance and IsoAir® Pro Series Particle Counters

Background on Vaporized Hydrogen Peroxide (VHP)

Vaporized Hydrogen Peroxide (VHP) is a strong oxidizing agent used to sterilize enclosed filling isolators. It’s been around for years, its applications growing in number. Robust sensors capable of withstanding these environments are needed to fully match the increasing use of VHPPortable particle counters can be removed from the area when cleaning takes place, but remote particle counters stay put when the VHP cleaning takes place. To meet this challenge, Particle Measuring Systems designed the VHP Resistant Particle Counter: the IsoAir® Pro Remote Particle Sensors have an internal flow path that is  resistant to the harmful effects of VHP.

Typically, particle counters subjected to VHP vapors cause a bleaching of the internal optical surfaces, resulting in an excess of scattered light from the laser source. In this blog, we discuss the testing performed on the sensor’s optical surface coatings in both static conditions and full VHP cycling tests where the instrument is in operation. Results were analyzed at each phase and then compared with the specifications given in ISO 21501-4:2018. All results were found to be within tolerance. The IsoAir Pro instruments are suitable for use in a VHP isolator environment.

On to the Tests…

All testing methods were designed to test the flow path of the IsoAir Pro instruments, not the external enclosure made of stainless steel. The focus of testing was designed to demonstrate the flow path’s material of construction, including the inlet jet, optical block, collection mirror and diode surround. The stainless steel enclosure is rated at IP65, and provides protection of the internal electronic. No damage to these components was noted during post testing analysis.

Two VHP tests were conducted on IsoAir® Pro instruments to determine how well VHP-resistant treatments performed under standardized conditions. They are described below.

1-year typical operation

Tested the internal optical flow path’s ability to withstand low concentrations of the oxidizing agent for long periods. Electronic components external to the flow path were not tested.

An IsoAir Pro instrument was exposed to VHP during normal sampling in 260 cycles, equivalent to one sample per day, 5 days per week for 52 weeks. Each daily cycle consisted of a minimum 400 ppm of VHP for 15 minutes. The instrument was verified periodically to make sure the instruments calibration maintained acceptable parameters throughout the testing cycle.

1-year simulated component surface test

The internal optics and flow path (not the electronic components of the particle sensor) were tested to determine their ability to withstand a high concentration of VHP for short periods.

Test Results
1-year Operation in VHP Environment Test

The IsoAir Pro instrument successfully maintained instrument counting efficiency, sizing accuracy and false count levels to meet ISO 21501-4 after over 1 year of simulated exposure to a VHP environment.

In addition to verifying system operation and calibration to ISO 21501-4:2018 requirements, physical inspection was made of the optical mirror to ensure no damage had occurred during testing. As can be seen in the figures below, the optical collection surface of the instrument sustained minimal discoloration from VHP exposure.

From right to left: Optical collection, sample chamber, beam stop

The sample chamber had VHP resistant treatment before installation or use. A traditional sample chamber with no VHP resistance treatment exposed to the same conditions shows bleaching of the sample chamber with the color shifting from black to a purple color. See the before and after comparison in the two following figures.

Typical non-VHP resistant sample chamber before (left) and after (right) 1 year of VHP exposure

Static Component Test

The IsoAir Pro instrument was also tested to demonstrate the individual internal components. Each component was separately exposed to VHP.

The aluminum components used for static component testing all started with a black coating. After 1 year of VHP cycles, the surface finish of the advanced VHP treatment still retained the light absorbing black color while the untreated and standard aluminum samples had degraded to a near raw aluminum finish. The advanced VHP treatment showed superior resistance to VHP cycles on the components of the optical block.

VHP Resistance Particle Counters

The IsoAir Pro-E and IsoAir Pro-Plus Aerosol Particle Sensors can withstand high concentrations of VHP vapor used in cleanroom maintenance. The lifespans of these products are extended by Particle Measuring Systems’ advanced VHP treatment, with the treatment tested and proven to last at least one year.

Read the full paper and see the VHP test results.

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