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Purpose
The purpose of a containment system is to filter dangerous or chemical, biological, or carcinogenic contaminants from air. Containment systems, as their name infers, are also designed to contain the filtered contaminants in a sealed housing until such time as the filter media needs replacement or regeneration. Containment systems can filter out particulates, gases, or both.
Containment systems can include a combination of several components, depending on the nature of the contaminant and application. These components can include prefiltration, test, high-efficiency or final filtration, and adsorber sections mounted in series. The capacity of the system can be increased by adding multiple sections to the system in parallel.
Containment systems can also include an option called bag-in/bag-out to facilitate the safe changeout of air filters. To learn more about bag-in/bag-out, click here.
Prefiltration
 The purpose of a prefilter is to remove larger particles from the airstream prior to the air entering the high-efficiency particulate or adsorber sections of the system. These filters help to increase the life of the higher value filters in the system and can be changed when needed to maintain the proper differential pressure. Prefilter tracks, which hold the filters in place, are often sized at 2" to 6" in depth. The graphic to the right is of a Farr 30/30®, a commonly used high-quality prefilter
Test
Test sections of two types are employed in containment systems, upstream and downstream.
Upstream test sections provide for the release and mixing of challenge aerosols or gases to test the effectiveness of the filters downstream. The challenge substance should simulate the real-life challenge that the system may see. Proper design is critical to ensure an effective filter challenge, as dynamics of the airflow must be properly accounted for to provide an evenly disbursed challenge of the proper concentration.
 Downstream test sections are where particle or gas detection takes place. In the case of particle challenging, the filters can be tested for overall efficiency or they can be scanned for leaks. Scanning is facilitated through the use of a particle counter nozzle, or probe, of a specific design for the application.
High-Efficiency or Final Filtration
Here's where some of the real work takes place. Generally the efficiency of the filters in this section are at a minimum 99.97% at 0.3 microns particle size (HEPA filters). Filters can be sealed to the housing with a gasket or fluid (gel) seal. It is important that no air bypass the filter media, as particles in the air that does bypass the filter media will contain a 100% of the upstream concentration of particles. Below is a photo of a Camfil Farr Absolute HEPA filter, commonly used in containment system high-efficiency filter sections.
Adsorber
If gases are of concern, an adsorber section is required. The adsorber section filters out molecular or gas-phase contamination using adsorbent media such as activated carbon or activated alumina. In some cases the adsorbent is treated on the surface with a chemical that reacts with or catalyzes the contaminant that lands on the surface of the media.
It is critical to select the proper adsorbent media for the application. In some cases, more than one media can be employed to filter out a larger array of molecular contamination types. In applications where the particular type of contamination is unknown, such as in building hardening, adsorbent medias of more than one type will be used. This strategy increases the chance that if a contaminating event occurs the correct adsorbent media will be available to remove the contamination from the air.
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