Filtration Table of Contents | Air Intake Filter Supplier
IEST-RP-CC001.319 classifies filter performance levels as:
Type A Filter Performance. Sometimes referred to as industrial types, these filters are tested for overall penetration at rated flow only. The filter retention (inverse of penetration) must exceed 99.97 percent for 0.3-m particles. ULPA filters greater than this value can be obtained upon agreement between the buyer and seller
Type B Filter Performance. In addition to the basic requirements for Type A filters, Type B units are certified free of significant pinhole leaks that would cause penetration at low flow rates. This type is tested at 20 percent of rated airflow with the filter encapsulated to disclose casing or gasket leaks. This type is sometimes referred to as nuclear-type.
Type C Filter Performance. In addition to the performance required of Type A filters, Type C filters, are tested with the use of air-generated test aerosols at 80 to 100 feet per minute (fpm) face velocity. The units are fully face-scanned to detect and eliminate all significant leakage streams greater than 0.01 percent of the upstream test aerosol concentration to which the filter is subjected. This type is infrequently called laminarflow type.
Type D Filter Performance. In addition to the testing required for Type C filters, Type D filters should be retested at their rated airflow and penetration, which should be no more than 0.001 percent of the upstream concentration. The filter unit should be encapsulated so that all components, including the filter pack, frame, and gasket, are subjected to testing. In the U.S., laser spectrometers are used to measure efficiencies of ULPA filters (>99.99999 percent).
Type E Filter Performance. Type E filters are designed, constructed, and tested in strict accordance with military specifications for HEPA filters intended for biological use.22 This type is for application in air cleaning or filtering systems involving toxic chemical, carcinogenic, radiogenic, or hazardous biological particulates. This type is referred to as a biological unit.