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Filtration Table of Contents
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Filter Supplier
HEPA filters have found many important
applications in the industrial, medical, pharmaceutical, and
microelectronic sectors. These diverse applications have
resulted in a number of industrial and governmental
specifications. In general, these specifications can be
grouped into five construction grades and three performance
types that provide a range of materials, manufacturing
techniques, performance characteristics, and costs for
different applications and user preferences. A standard
covering the grades and types of HEPA filters has been issued
as IEST-RP-CC001.3 by the Institute of Environmental Sciences
and Technology. This standard lists the following
classifications.
Filter Construction Classification Grades
Grade 1 – Fire-Resistant Filters. Filters
of this grade must contain fire-resistant materials that may
ignite when the filter is exposed to hot air or fire, but
will not continue to burn once the ignition source is
removed. The filter must exhibit a specified retention
efficiency after exposure to no more than 700 ± 50 degrees
Fahrenheit (371 ± 10 degrees Celsius). These filters comply
with ASME AG-1, Section FC.2
Grade 2 – Semicombustible Filters. This
grade costs less, but provides a lower level of protection
against elevated temperature than Grade 1. For this reason,
the user should evaluate application of this filter grade
with the individual fire propagation hazards in the area of
use. This filter type will fail at temperatures much lower
than Grade 1. These filters comply with UL 586.20
Grade 3 – Combustible Filters. This
grade covers filters required for certain service
requirements that permit acceptance of the combustibility
hazard. Grade 3 filters are readily combustible and are used
only where high-value product recovery by incineration is
desirable, disposal of volumes are critical, or exposure to
chemical atmospheres might be incompatible with the use of a
HEPA filter incorporating a medium of glass fibers. It should
be noted that manufacture of a combustible HEPA filter medium
formulated from asbestos and cellulose has been discontinued
for more than a decade because of the hazards associated with
its use and the resulting low demand. Specialty filter media
for recovery of precious metals by incineration are still
available. These filters comply with UL 900, Class 1.21
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