HEPA

HEPA ( High Efficiency Particulate Air ), ULPA (Ultra Low Penetration Air ) filter and Sulpa (Super ULPA ) filters are designations with a certain particle class. Filters of this class are used to filter out viruses, respirable dust, mite eggs and excretions, pollen, smoke particles, asbestos, bacteria, various toxic dusts and aerosols from the air.

History

These types of filters in the 1940s was developed as part of the Manhattan Project in order to remove the previously unknown but dangerous radioactive particles from the air can. After the Second World War, these filter classes were made available for other purposes and classified in stages.

Area of ​​application

They are used among others in the medical field, so in operating rooms, intensive care units and laboratories, and in clean rooms, in nuclear engineering and in some air scrubbers. For the selection of filters, each class of application is crucial. For the classification of spaces in different cleanroom classes to use the EN ISO 14644th

Especially for non-industrial applications ( eg, vacuum cleaners ) are a variety of filters on offer, which, although the term HEPA in their name, but not the specifications of, for example, guarantee EN standards. Even outside the territorial scope of the EN standards is the term HEPA filter in use. Here, however, very different, partly non-comparable test conditions for the designation to be applied.

Efficiency and standardization

European standardization

For the classification of the different filter efficiencies, the particle filter classes from 1 to 17 are used in Europe. The higher is the number used for the higher degree of separation of the guaranteed. The European standard for the classification of the particulate is EN 1822-1:2009 with the filter classes E10 -E12 (EPA ), H13 - H14 ( HEPA) and U15 - U17 ( ULPA ). According to the well-known filter effects are particles 0.1 to 0.3 microns hardest deposit ( MPPS = most penetrating particle size) - therefore (H ) EPA and ULPA filters are based on their effectiveness against these grain sizes by DEHS ( = di- classified 2 -ethylhexyl sebacate ) - test aerosol. Larger and smaller particles are deposited due to the better physical properties. A distinction is made between the overall efficiency of the filter and the worst local authority.

EPA-/HEPA-Filter

ULPA filters

Other values ​​for the degrees of separation 1 to 9 ( coarse and fine filter to EN 779 ) see Article particle classes.

United States

Unlike the scope of European standards is on the territory of the United States, only the term HEPA filter with fixed separation. The separation efficiency is comparable to the filter class H13 of EN 1822-1:1998. He is according to DOE -STD 3020 from 97 to 99.97 percent for particles with a size of 0.3 microns.

Technology

The filter mats used to be mounted in most cases in plywood or metal frame, so you can easily switch to. The filter medium itself, as with most fiberglass mats, air filters, which have a fiber diameter of about 1-10 microns. For enlarging the filter surface, they are usually incorporated wavy or jagged in the frame. When changing the filter is a high risk of inhaling the carefully filtered pollutants or touch. Therefore special filter housings are used in many cases, which allow a non-contact filter change. This method is called the protective bag exchange method.

Operation

The process of particle deposition in the filter is generally done in four different ways:

  • Sieve effect: particle sticking ( in HEPA filters are not relevant due to the small particle ) due to their size between the filter fibers.
  • Inertia effect: Larger particles do not follow the air stream ( to the filter fiber around), but collide due to their inertia against it and stick.
  • Diffusion effect: very small particles (< 1 micron ) do not follow the air stream, but through their collisions with the air molecules, a Brownian motion similar trajectory and thereby come together with the filter fibers, where they adhere.
  • Filter ( fluid power )
  • Environmental
  • Filtration
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