By Adam West, Course and Curriculum Manager at CriticalPoint
HEPA Filter Basics
HEPA filters are part of our everyday life. These filters are essential to anything that provides air quality improvement—think household vacuums, inside our cars, and especially indoor spaces with high foot traffic. This is because HEPA filter design reduces dust, pollen, mold, bacteria, and common-size airborne particles. The less we are exposed to these particles, the better it is for our overall health, particularly in close quarters.
Generally speaking, filters improve air quality in any environment. But not all HEPA filters have the same level of filtration. For instance, vacuum filters can only do so much, and HVAC systems with basic filtration capture macro particles while allowing smaller particles to skate through. In contrast, specifically designed spaces require an efficiency rating of 99.9XX percent or better, capable of filtering particles as small as 0.3 micron (in comparison, a single red blood cell is about 7 to 8 microns). Pharmacies that have a compounding cleanroom and ISO Class 5 devices require this level of HEPA filtration!
The air cleanliness classification of our cleanrooms and compounding devices cannot achieve ISO Class 5, 7, and 8 without HEPA filtration. Compounding pharmacies rely on certification services to determine the condition of each filter. Certifiers not only tell you whether the filters have passed leak testing but, in many cases, also provide information on the HEPA filter’s remaining lifespan and when you can expect to replace it.
Do HEPA filters leak?
YES! All filters “leak” or allow some level of “contamination” through. Otherwise, airflow could not pass through the filter too! This is why it is important to understand the level of performance and the efficiency rating of the filters required in compounding environments. Particles 0.3 microns in size are incredibly tiny. Anything smaller that doesn’t get trapped or filtered is not likely to be a threat to the environment or to our health if present in the space. This is because viruses, bacteria, and dust particles range in size from 0.045 to 5.0 microns. Filters that have an efficiency rating of 0.3 microns filter out potential viable (living) threats of that relative size and greater, thus making the environment suitable for sterile compounding (at least until the presence of people and activity begins).
Understanding this information directly correlates with ISO classifying our spaces. In the certification report for nonviable total particle count testing, the target micron size should be ≥ 0.5 microns. That data concentration value describes the performance of your room’s cleanliness down to at least 0.5 microns, because anything of that relative size and greater (in large quantities) could be a living or dead particulate or a larger nonviable particulate that a smaller living particulate can use as a vehicle to circulate in your spaces.
The good news is that the lower the concentration units reported in your room under true dynamic conditions the better the environment is doing in real time. This is what establishes your environment to a certain ISO class level (e.g., 5, 7, and 8). The reported data provides a visual representation of the room performance and the filter’s ability to continuously capture particles before delivering filtered air to the space AND while the room is being challenged with dynamic activity. I’m a nerd, I know. But it’s why I always say cleanrooms are living creatures. They eat, sleep, and breathe performance characteristics.
Speaking of Living Creatures
Particle counters that collect and enumerate particulates don’t care if the particle is living or dead. It just detects a particle size and sorts it in the data expression. In keeping with everything said already, know that particle counting during certification is just a snapshot in time. At every six-month certification, certifiers test and grade the level of cleanliness of the environment at the time of testing—and not during all those other moments in between! And because we are concerned about the micron-size particles present (despite being in a filtered environment) and the possibility of these particles being alive, it is important to monitor the presence and level of viable organisms more frequently than every six months, particularly during those in-between moments when a particle counter is not used.
Viable environmental monitoring seeks to recover the living organisms that exist in the cleanroom despite the first line of defense offered by HEPA filtration. Living organisms are not present because they slipped through the HEPA filters in the ceiling; no, they likely are introduced into the environment from items brought into and people entering the spaces. It’s the outside influences and activity in the spaces that affect cleanroom design and performance. In theory, a cleanroom can maintain a fairly immaculate environment if left static.
Maintaining a Microbial State of Control
It’s the day-to-day operations that matter most. Activities and outside influences are what challenge the cleanroom’s ability to properly maintain an ISO-classed space. The HEPA filters do their job by creating a clean environment. A six-month certification interval determines the performance of the space and qualifies the room’s ISO class at a specific point in time. The room is “clean”… until our activity introduces the microbes. Cleanrooms don’t do all the work to prevent microbial contamination! Our conduct in these environments is what determines the performance of the HEPA-filtered environment during dynamic conditions. Therefore, having an awareness of the behavioral impact we have on these environments is critical.
Viable air and surface sampling results are crucial to understanding the day-to-day operations. Our cleanroom etiquette and behaviors directly correlate with being able to control and maintain low levels of expected contamination. You should know, based on the microbial results, what a typical workday would look like from the perspective of a state of microbial control. That level of understanding and trending gives peace of mind for all of those in-between moments when we aren’t sampling. To a certain extent, it can be said that the room operates as expected on the days sampling is not performed. This, of course, is provided that staff behavior does not negatively affect cleanroom performance.
What keeps a HEPA filter happy?
It’s routine certification testing, but that’s not the entire story. We understand when a HEPA filter passes or does not pass certification at the six-month interval. If failed, it’s likely that one or more of the following arose:
- The filter has loaded up with particulate to point where airflow is reduced and can no longer support the velocity or air changes per hour (ACPH) needed for a particular environment.
- Damage to the filter has occurred at some point between certification.
- An existing silicone repair no longer supports the minimum leakage allowance.
However, HEPA filters can last several years if properly maintained through prefiltration and frequent changes of the prefilters. Monitor your prefilters whether they are in the ISO Class 5 devices or the cleanroom HVAC system. Depending on the season and geographic region, this could be scheduled every 3 or 6 months. Keep in mind that, in the spring and fall, prefilters may need to be replaced on a monthly basis in the HVAC systems.
Make sure that you include in your cleaning SOPs to inspect the prefilters of the ISO Class 5 devices every month during cleaning, and determine if the prefilters are visibly loaded with particulates. They may only need a change-out every 6 or 12 months because they live in the cleanroom.
In the event that you need a HEPA filter change, CriticalPoint recommends working with your certifier to obtain the information needed to order the correct HEPA filter type for the application. It’s also a great way to have a worry-free, turnkey solution when installing and certifying HEPA filters. Click here to learn more about training on engineering controls and how they operate during dynamic conditions.
View our Best Practices for Nonhazardous Sterile Compounding Course