Biological safety cabinets commonly use High-Efficiency Particulate Air (HEPA) filters and Ultra-Low Penetration Air (ULPA) filters. But what exactly differentiates HEPA air filters from ULPA air filters in these cabinets?
1. Structure and Working Principle
From both structural and chemical perspectives, HEPA and ULPA air filters are very similar. These filters are installed in biological safety cabinets where airflow, driven by a motor, carries harmful gases and particles. Both types of filters use randomly arranged borosilicate (glass) fiber mats with fiber diameters ranging from 0.5 to 2 micrometers. The gaps between the mats allow smoke, chemicals, gases, and vapors to pass through the filter to the exhaust, removing them from the local atmosphere. Particles carried by the airflow are trapped within the filter, effectively removing them from the air.
The main difference lies in density: ULPA filters use a higher density of glass fibers to capture particles. This higher density allows ULPA air filters to trap smaller particles than HEPA filters. In biological safety cabinets, filters are designed not only to remove airborne particles but also to prevent clogging from electrostatically attracted dust particles.
2. Particle Removal Efficiency
HEPA and ULPA air filters are regulated under NSF/ANSI 49 standards. Each type of filter must meet specific characteristics and performance levels to be classified as HEPA or ULPA. According to NSF/ANSI 49, biological safety cabinets use C- or J-type HEPA filters, while ULPA filters use F- and K-type filters. Testing follows IEST-RP-CC001 methods.
- C-type HEPA filters must remove at least 99.99% of 0.3-micron particles.
- J-type HEPA filters must remove 99.99% of particles ranging from 0.1–0.2 microns or 0.2–0.3 microns.
- F-type ULPA filters must remove 99.999% of particles from 0.1–0.2 microns or 0.2–0.3 microns.
- K-type ULPA filters must remove 99.995% of particles in the same size ranges.
ULPA filters always remove more particles due to stricter test efficiency. According to EN1822-1, an air filter must achieve 99.9995% efficiency at the Most Penetrating Particle Size (MPPS) to be classified as a ULPA filter.
3. Cost Differences
ULPA air filters typically cost about 35% more than HEPA filters of the same size. But the total cost is not limited to the filter itself. ULPA filters generally have a shorter lifespan—HEPA filters last 10–15 years on average, while ULPA filters last 5–8 years. Therefore, using ULPA filters increases maintenance and replacement costs.
The higher density of ULPA filters also increases airflow resistance in the cabinet. Overcoming this often requires larger or multiple blowers, which raises installation and maintenance costs compared to standard-sized single blowers. Moreover, airflow through ULPA filters is reduced by 20–50% compared to HEPA filters. To maintain the same air volume, a ULPA air filter requires more force than a HEPA filter of the same size.
To maintain equivalent airflow and protection using ULPA instead of HEPA filters, manufacturers may need to:
- Increase filter depth,
- Expand filter surface area, or
- Boost motor or blower power.
Increasing filter depth or area can allow more air to pass, but it may also require enlarging the biological safety cabinet, potentially increasing the cabinet’s purchase cost.
