How often should HEPA filters be replaced in a clean room? Every clean room operator faces this question at some point and it quickly becomes an important issue while considering replacement and maintenance costs. In the following, we provide an overview on HEPA filters, HEPA filter testing and give some expert tips on HEPA filter replacement frequency.
Table of content
- What are HEPA filters and why is HEPA filter replacement frequency important?
- Why is HEPA filter change frequency so important?
- Applicable GMP and ISO guidelines
- Best practices for HEPA filter change frequency
- Determine How Dirty Your Cleanroom Is
- Rule of Thumb for Replacements
- Extend your filter’s lifespan
- Keep track of replacements
- How is HEPA filtration system tested?
What are HEPA filters and why is HEPA filter replacement frequency important?
In order to keep cleanrooms functioning at the required standards, special filters are in use.
These special air filters are called HEPA filters. What’s important about HEPA air filters is that they are incredibly effective at capturing particles of almost all sizes. articulate air filters are made of either plastic (PP + PET) or fiberglass and can capture viruses, bacteria, pollen, PM2.5, allergens and are also highly effective at capturing nanoparticles. Filters containing an adsorbent or catalyst such as charcoal may remove odors and gaseous pollutants such as volatile organic compounds or ozone. HEPA filters are also the most important component of any air purifier.
What standards define HEPA filter replacement frequency and HEPA filter life?
HEPA stands for the ability to fulfill a strict set of requirements.
In Europe HEPA filters must remove 99.95% (ISO) of particles, in the US they must remove 99.97% of particles that have a size greater than or equal to 0.3 μm.
Filters that capture ≥ 85% of particles, but less than 99.95% are called EPA filters or ‘efficient particulate air filters. These air filters do not meet filtration requirements to be considered a HEPA air filter. On the other hand, filters that exceed the requirements of a HEPA air filter and capture more than 99.999% of particles are called ULPA filters or ultralow penetration air filters. These are more expensive as their efficiency and their medium resistance level is higher.
To extend HEPA filter life and reduce how often HEPA filters need to be changed, preliminary filters are used: usually fine particulate air filters like F7 and F9 filters (EN779). These pre-filters must be replaced regularly, following HEPA filter replacement guidelines, as they protect HEPA filters from clogging and help optimize performance in both hospital and pharmaceutical settings.
Pre-Filter replacement frequency
Pre-filters should usually be replaced every 6 months, but if the air is very dusty or the system runs under heavy use, it's a good idea to check them every 2 to 3 months and replace them sooner if needed.
The cleanliness class of the clean room can also affect HEPA filter lifespan, as ‘dirtier’ environments require more frequent HEPA filter replacements.
Why is HEPA filter change frequency so important?
Integrity of HEPA filters is essential to assure required cleanliness levels in a cleanroom. However, there are other relevant aspects that are worth considering when deciding on how often the filter should be replaced.
One of those aspects is the load on the filter and the pressure drop. Should the pressure drop get too high, the ventilation system will start working at an increased rate to maintain the prescribed air exchange rates, resulting in higher energy demands. If we experience a jump in operational costs in this case, it's a strong indicator that the HEPA filter change frequency should be adjusted. In such cases, replacing the filter is not only justified but may be the most efficient option based on HEPA filter replacement guidelines.
Applicable GMP and ISO guidelines
Maximal HEPA filter life is not specified in GMP or ISO guidelines. However, both GMP and ISO 14644-3 standards require regular integrity (leak) testing at intervals of 6 to 12 months, depending on the cleanroom classification.
What is clearly stated is that, according to GMP, the filter must be free of leaks at all times. Leak tests must be performed every six months in ISO 1–5 zones and every twelve months in ISO 6–9 environments. If a filter fails the test, it must be replaced immediately This directly affects HEPA filter replacement frequency and reinforces the need to follow proper HEPA filter replacement guidelines.
The KleanLabs semi-active and dynamic clean room pass box models are also equipped with built-in HEPA filters
HEPA filter replacement frequency best practices
1. Determine how dirty your clean room is
Recommended replacement frequency of HEPA filters will greatly depend on how dirty your cleanroom is.
For instance, ISO 8 rooms do not require gowning rooms, hence are much dirtier than ISO 5 rooms, as they are the least clean in terms of cleanliness classification. The burden on the filter will also be greater in an ISO 8 cleanroom than in an ISO 5 environment. In case of some cleanrooms, this extra burden may result in having to exchange HEPA filters on a yearly basis.
Also, keep in mind that an increased load on the filter may result in higher energy demand as the ventilation system needs to work at an increased speed to compensate.c.
2. Rule of thumb for replacements
There are companies that swear by replacing the HEPA filters every 3 years. The maximum lifespan of HEPA filters we’ve heard of from our clients is around 8 years, which doesn’t mean it has reached its maximal life expectancy by then. As long as filters are assessed regularly and deemed effective, they do not have to be replaced.
3. Extend your filter’s lifespan
Factors that impact life expectancy of filters are:
- the volume and pollutedness of the filtered outside air,
- the volume of recirculated air filtered,
- aerosol challenge exposure frequency and duration,
- the efficiency of the pre-filtration method(s) used.
Keep in mind that if your filters are custom-made, delivery after placing an order might take longer and will also result in higher costs. This is why regular checks and preventative measures will go a long way.
In the last few years there has been a shift in the manufacturing industry from preventive to condition-based maintenance (CBM). There are a series of sensors that observe the state of different parts and as a consequence, maintenance is only performed when certain indicators show signs of decreasing performance or failure. This technology allows using air filters for exactly the optimal amount of time.
4. Keep track of replacements
The person replacing the filter should always sign and date the filter for the sake of clear workflows. Thus, if anyone new will have to deal with replacements, they’ll have full access to data in a very transparent way.
How is HEPA filtration system testing performed?
Testing the performance of air filtration systems in clean areas is critical to maintaining the cleanliness of the production environment.
Dispersed oil particulate (DOP) scan testing, also known as filter integrity testing, or leak testing, is one of the most frequent methods by industry standards. The test is recommended to be repeated at regular time intervals to verify the continued efficiency of the filter. During the test, the filter undergoes an aerosol probe, meaning that it is challenged by introducing particulates to the air and the output is measured.
Spatial uniformity of aerosol probe
To perform an accurate filter leak test, the aerosol concentration must be evenly distributed across the entire upstream face of the filter(s) being tested. In other words, the aerosol must show spatial uniformity. Without this, areas with too high or too low aerosol concentration could cause the filter to incorrectly pass or fail the test. According to ISO 14644-3, the variation in aerosol concentration over time should not exceed ±15%.
Testing for potential leaks between the filter frame and housing
HEPA filters have a space between the filter frame and its housing.When testing for gasket leaks between the filter frame and housing, the probe is inserted into that area and then the area is scanned to determine S local collection efficiencies. Based on these measurements, leak rate and overall efficiency of the filter called integral value are calculated. If a leak is found on the filter, it can be fixed following a fill patching procedure.
HEPA filter 10-year lifetime evaluation
A study looked at whether HEPA filters can last up to 10 years without needing to be replaced. The filters were checked every year to make sure they still worked well, mainly by testing airflow, pressure, and how well they trapped particles.
The results showed that most filters lasted the full 10 years without any problems. Only a few had to be replaced early. When filters are used in clean, dry conditions and checked regularly, they can stay effective even beyond 10 years.
This means it may be better to replace HEPA filters based on how they perform, not just their age. Regular testing helps make sure the filters still work and are not replaced too early or too late.
