Terminal HEPA filters

Are terminal HEPA filters on room air supplies necessary to prevent risk of product migration from one manufacturing area to another through ductwork distribution systems when air handling plant is inoperative ... 

Standard type (turbulent flow) diffusers should be used in class 100,000 areas. Terminal HEPA filters should be used in the ceilings of the areas that are class 10,000 or cleaner. 

Class 10,000 or cleaner areas have terminal HEPA filters in the ceiling. 

Measure the average face velocity of each terminal HEPA filter. Measure the average velocity 1 ft above the workspace, exposed product areas, or exposed component areas in all Class 100 laminar flow rooms or areas. 

All terminal HEPA filter face velocity measurements are within 30% of the average filter velocity. 

The average face velocity of terminal HEPA filters servicing Class 100 laminar flow rooms is 90 ft/min 20%, with no points below 75 ft/min or above 105 ft/min. 

Fig. 5 (A) The self-contained terminal HEPA filtration module (TFM). (B) Arrangement of TPMs in the T-Bar ceiling in a conventional-flow application. (Courtesy of American Air Filter, Inc., Louisville, Kentucky.)...

Conventional airflow (also known as turbulent, or non-unidirectional airflow) incorporates HEPA filters, located in-duct, or as room terminal filtration modules (TPMs Fig. 5). Often confused with LAP, conventional airflow does not meet that definition because it allows multiple-pass circulating characteristics or a non-parallel airflow direction, or both. This type of airflow is incapable of producing first air, and is normally used as secondary or buffer filtration in treating a processing or compounding space that contains laminar airflow devices (LAFDs) to maintain primary critical work surface conditions, or in treating other... 

The terminal HEPA filtration module (TFM) is a self-contained HEPA filter and plenum unit (Fig. 11), which may be used to provide laminar or conventional airflow to a clean space, or may be dedicated as a LAF workstation.f The TFM is available with a 10 in. (optional 12 inch) collar for connection by a circular supply duct to a central air handling system (Fig. 5A) or as a free-standing, fully powered unit containing a motor and blower. It is normally installed in a... 

HEPA filters may be located in the air-handling unit or placed terminally. 

Housings for terminal HEPAs should have airtight seals to the ceiling behind the grilles or diffusers. The sealing of the HEPA filter should be on the air-inlet side of front-withdrawal HEPAs and on the air-outlet side of back-wiih-drawal HEPAs. Filter housings should be equipped with an access port behind the filter to allow access of smoke for validation purposes (see below). 

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