CBRN Filtration Fundamentals

Hunter however, has taken the same proven designs originally developed for the military and incorporated that technology into its complete line of commercial Homeland Security CBRN filtration systems. These systems are designed with high efficiency HEPA filters and specially designed carbon adsorber filters containing ASZM-TEDA impregnated activated carbon absorption media designed to remove a wide variety of military grade toxins.

Today, Hunter continues with the development of new CBRN filter designs which not only can protect against military grade toxic agents but can also protect against a wide array of Toxic Industrial Chemicals (TIC) addressing the threat from either intentional or accidental releases of toxic industrial chemicals. Systems incorporating this next generation of filters can be installed to help protect schools, commercial building or other structures located in the path of a potential TIC release.

About HEPA particulate filters
HEPA filters were developed by the Atomic Energy Commission during World War II to remove radioactive dust from their plant exhaust. HEPA filters are now the primary filtration systems for electronic clean room assembly, isolation wards, surgical theatres, bioengineering, pharmaceutical processing and any application where maximum reduction or removal of sub-micron particulate is required.

HEPA filters maintain efficiency over a life span of two to five years depending on operating conditions. As specified by Hunter, they are 99.97% effective by particle count down to an average of 0.3 microns (including bacteria, fungal and other opportunistic micro-biologicals) which is 1/75,000th of an inch or 1/300th the diameter of a human hair. It becomes even more effective below the 0.3 micron particle size due to decreased face velocity of the particle slamming into the surface of the filter material. HEPA filters do not require any cleaning or maintenance to maintain effectiveness. All Hunter HEPA filters are leak tested according to industry and military standards. This is the most reliable method of challenging a HEPA filter system against an aerosol. It measures and compares the downstream concentration to the upstream concentration of the aerosol to determine the system penetration. It must be <=0.03%, or negligible.

About activated carbon gas and vapor adsorption filters
Typical commercial activated carbon air filters are designed to remove many common airborne contaminants but are not designed to effectively protect against many deadly CBRN agents which could potentially be used during acts of terrorism. These CBRN agents can only be effectively removed by using specially treated carbon "adsorption" filters.

The most effective activated carbon adsorption filter medium to protect against the effects of toxic CBRN agents is a highly activated carbon with metal coating enhancement. The two most common metal coatings used in the western world are ASC-TEDA (Copper-Silver-Chromium-Trietheylenediamine) and ASZM-TEDA (Carbon-Activated, Impregnated, Copper-Silver-Zinc- Molybdenum-Trietheylenediamine) military grade activated impregnated carbon. ASC-TEDA is no longer used in the U.S. because of its chromium content. The ASZM-TEDA coating is patented by the U.S. Army and offers the best chemical protection available. It is the only grade of carbon deemed acceptable for collective and personal CBRN protection systems and devices by the U.S. Army.

A carbon adsorption filter removes molecules from the air stream by the process of adsorption, trapping molecules in the pores of the carbon granules. This system works best against large molecules, that is, chemicals of low vapor pressure. Activated carbon is an effective sorbent for removing a broad range of chemical vapors because of its extensive micro porosity and range of pore sizes. Typically the pores in highly activated carbon have a total surface area of over 1.000 square meters per gram.

Filtering chemicals of high vapor pressure -- small molecules -- requires a chemical reaction with impregnates (coatings) added to the carbon as in ASZM-TEDA process carbon. These impregnates react with the toxic gas through the filter to form products that are either innocuous or that can be "grabbed", or adsorbed, and retained by the filter.

No filters available on the market provide protection from as wide a range of adsorbable chemicals and biological agents as Hunter filters and filter systems. Through our Applied Research Center in Edgewood, Maryland and joint development and testing efforts with the U.S. Army, Hunter is continuing to develop effective filtration technology to protect against an even wider range of chemicals including the most common and dangerous Toxic Industrial Chemicals / Toxic Industrial Materials (TIC/TIMs).

All Hunter Homeland Security products and systems have been thoroughly tested for the effective removal of a wide range of CBRN agents which comprise the greatest threat from either acts of terrorism or accidental release.