Ensuring that a facility’s HEPA filters are in good working order is critical to safe, effective cleanroom practice. While the current USP <797> chapter requires that cleanroom HEPA filters be tested only upon installation, with a minimum filter efficiency of 99.99% on 0.3 micron particles, upcoming changes to the USP <797> framework, effective December 1, 2019, require HEPA filters to be leak tested semiannually as part of recertification.
The revised USP <797> chapter states1:
Certification of the classified areas including the PEC must be performed initially, and recertification must be performed at least every 6 months and must include . . . HEPA filter integrity testing: HEPA filters must be leak tested at the factory and then leak tested again after installation and as part of recertification.
The Leak Testing Process
During the leak testing process, filters are challenged with particles or aerosols of a specific size, and the penetration of each filter is recorded. This method can reveal leaks in the HEPA filter and frame or housing gaskets and/or seals.
There are multiple testing methods available. One method involves creating challenge aerosol by blowing compressed air through a laskin nozzle into a tub of oil (typically polyalphaolefin [PAO]). Another test is Dispersed Oil Particulate, wherein dispersed oil particulate is evaporated by heat and the vapor injected into the airstream in front of the test filter. As the vapor condenses back to ambient temperature, it forms uniform droplets about 0.3 microns in diameter. Particle concentrations can be measured using light scattering instrumentation upstream and downstream of a HEPA filter. Our organization, Texas Oncology Round Rock in Round Rock, Texas, opted to use Dispersed Oil Particulate testing.
Challenge Port Installation
In order to challenge test ceiling HEPA filters for performance and detect any leakage, there must be a way to introduce an aerosol into the ductwork for each filter. This requirement should be taken into consideration when a new cleanroom is designed. However, many older facilities may not have a system in place to facilitate leak testing and will need to be retrofitted.
Ideally, every HEPA filter should be separately tested. Our organization purchased a HEPA Filter Aerosol Challenge Port Kit from a cleanroom parts vendor (see PHOTO), which may be appropriate for most cleanroom designs. The materials used, including an aluminum, powder-coated port with a polypropylene plug that can withstand the solution utilized for cleaning, are suitable for cleanroom use. The vendor also offers a solution for flexible HVAC tubing, which can present another challenge in the retrofitting process. For example, installation of the challenge port parts can cause rips in inflexible HVAC tubing; in addition, inflexible HVAC tubing does not provide sturdy placement, as it could rip once the steam is introduced during the HEPA filter testing. Successful installation of the challenge port kit is achieved utilizing a durable metal sleeve that is wrapped around the flexible HVAC tubing. The metal sleeve provides a firm surface for the introduction of the challenge port parts.
Installation of challenge ports can be performed by the vendor’s technicians within a few hours (depending on the number of ports needed and the accessibility of the duct work). This work should be performed after hours, and a terminal cleaning process must follow once the installation is complete.
Conducting HEPA Filter Integrity Testing
The cleanroom certification company will utilize the challenge ports to evaluate the efficacy of the HEPA filter(s). Data obtained from these readings can help determine if a HEPA filter needs to be replaced or repaired, or if gaps around the filter housing are present. The test results are especially useful when a facility is presented with failed air samples due to the introduction of unfiltered outside air. Conversely, the test results also may serve to assure pharmacy that the HEPA filters are working as intended and are compliant with USP <797> requirements.
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