Difference between HEPA filter and ULPA filter in biosafety cabinet

Difference between HEPA filter and ULPA filter in biosafety cabinet


The filters used in the biosafety cabinet are generally high efficiency particulate air (HEPA) filters and ultra-low permeability (ULPA) filters. What is the difference between HEPA and ULPA filters?

I. Structure and working principle of HEPA and ULPA filters

Structurally and chemically, HEPA and ULPA filters are very similar. These filters are used in biosafety cabinets where the airflow (driven by a motor) carries harmful gases and particulate matter. Both types of filters use randomly arranged pads of boron silicate fibers (fiberglass) between 0.5 and 2 microns in size. The gap between the pads allows smoke, chemicals, gases, and steam to move through the filter to the exhaust port, removing gases from the local atmosphere. The particles carried by this stream do not pass through the filter and get stuck, removing them from the atmosphere.

The main difference between the two filters is that ULPA uses higher density glass fibers to capture particles, while higher density ULPA filters are able to capture smaller particles than HEPA filters. The filter in the biosafety cabinet is not only to filter particles in the air, but also to prevent electrostatic adsorption of fine dust particles, so as not to plug the holes in the filter.

2. Remove particulate matter

Both HEPA and ULPA filters are governed by the NSF/ANSI 49 standard. Different filters must have certain characteristics and achieve certain performance levels to be classified as HEPA or ULPA filters. The standard NSF/ANSI 49 requires the use of type C or J HEPA filters for biosafety cabinets and type F and K filters for ULPA filters. The filter needs to meet the test standards developed using the test-Iest-Rp-CC001 test method. Using these methods, Type C HEPA filters must remove particles up to 0.3 microns with at least 99.99% efficiency, while Type J HEPA filters must remove 99.99% particles up to 0.1 to 0.2 microns or 0.2 to 0.3 microns.

For ULPA filters, Type F filters must remove 99.999% of contaminants from 0.1 to 0.2 or 0.2 to 0.3 microns, The K-type ULPA filter must remove 99.995% of 0.1 to 0.2 or 0.2 to 0.3 micron particles. Like HEPA filters, ULPA filters can remove particles smaller and larger than the test size, but ULPA filter tests set inefficiencies so ULPA filters always remove more particulate matter from the air than HEPA filters. According to EN1822-1, an efficiency of 99.9995% must be achieved for penetration particle size (MPPS) to be classified as an ULPA filter.

3. Cost differences

ULPA filters are typically 35% more expensive than HEPA filters of the same size. However, it's not just the cost of the filter itself to consider. Since ULPA filters generally have a shorter service life than HEPA filters, with an average service life of 10-15 years for HEPA filters and an average service life of 5-8 years for ULPA filters, compared to HEPA filters, Using ULPA filters will cost more in maintenance costs and filter replacement.

The higher the density of the ULPA filter, the greater the resistance generated by the airflow dynamics of the cabinet. This is usually overcome by using larger blowers or multiple blowers, which are also more expensive to install and maintain than a single standard-sized blower. In addition, air flow through ULPA filters is reduced by 20-50% compared to HEPA filters. To push the same volume of air through an ULPA filter, it takes more force to do so than it would with a HEPA filter (assuming the same size).

Therefore, to use an ULPA filter instead of a HEPA filter to maintain the same level of airflow and protection requires either an increase in filter depth, an increase in filter area, or an increase in motor or blower power. When increasing the filter depth/area, it will increase the amount of air that can pass through, but you may need to increase the size of the biosafety cabinet, which may increase the cost of purchasing the biosafety cabinet.