High Temperature HEPA Filters FAQs Technical Bulletin

TECHNICAL BULLETIN
Life Science & Microelectronics
High Temperature HEPA Air Filters FAQs
HEPA filters, when exposed to
elevated temperatures, present
multiple challenges for filter
performance and filter integrity
testing. It is one of the few areas
of air filtration where there are
simply no black or white answers.
To summarize Camfil’s experience
on this subject, the following
are some recommendations and
answers related to high temperature
filters.
What is the primary application
of HEPA filters at elevated
temperatures?
These filters are used in ovens and
tunnels designed for use in the
Life Science and Microelectronics
industries. This equipment may
be performing sterilization and
depyrogenation of instruments
or glassware (vials) in Life
Science and die-bond curing or
other semiconductor packaging
processes. Applications can range
in temperature from 212° to 752° F
(100° to 400° C) and require ramprates (burn-in) from steady state
to as much as 60° F + per minute
(15°+ C/min.). These variations
create tremendous stress and
challenge to the filter’s construction
and therefore filter performance
integrity.
filter is the red high temperature
silicone potting compound used
to seal the metal-separated media
pack to the metal filter frame. There
are sometimes slight manufacturing
differences, with different locations
within Camfil. European (EU)
manufactured filters in this class
are rated at 482° F (250° C), in the
United States (US) they are rated at
500° F (260° C).
What are the options for
conventional high temperature
filters?
The other high temperature HEPA
filter type has a white ceramic
sealant, and is most commonly
used in the “hot” zone of a tunnel
and for other very high temperature
applications. These filters
incorporate a ceramic material to
seal the metal-separated filter pack
to the metal frame. Again, there are
slight differences in temperature
ratings due to some specific design
criteria, EU is rated to 662° F (350°
C) and the F series in the US is
rated to 750° F (398° C).
There are two common types of
high temperature HEPA filters, in
simple terms, silicone and ceramic
sealed filters. For the silicone
type, one is for moderately high
temperature and is often used in
the supply and exhaust (“cool”
zone) of an oven in addition to the
recirculated HEPA filters and for a
variety of other applications. The
distinguishing characteristic of this
Two Different Examples of Burn-in Procedures
from Major Life Science End Users
in North America and Europe.
Oven Temperature Burn-in Procedure
800 / 1472
700 / 1292
Temperature
752 / 400
( F° / C° )
( F° / C° )
Temperature
Oven Temperature Burn-in Procedure
572 / 300
392 / 200
600 / 1112
500 / 932
400 / 752
300 / 572
212 / 100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Time
(hours)
200 / 392
100 / 212
0
5
10
15
20
Time
(hours)
www.camfil.com
25
30
35
High Temperature HEPA Air Filters FAQs
Are there improved high
temperature filters available?
There has been specific high
temperature filters developed
in conjunction with equipment
manufacturers and end users.
The Termikfil design features a
monolithic inorganic, non-metallic
frame. The unique design and
assembly method allows all of
the bonded materials to react to
temperature changes in a similar
manner. This reduces thermal
stress and helps to ensure a
product that is more resistant
to multiple cycles and rapid
temperature changes. Metal
components, such as the grille, are
designed to “float” and not interfere
with other components as they
expand and contract in response
to temperature changes. This filter
is rated at 662° F (350° C) and
is delivered ‘burned in’ at 300° C
(573° F) from our facility in France.
There is also a V-bank type HEPA
filter that is rated to 446° F (230°
C) continuous, with one hour peaks
to 482° F (250° C). This filter is
used where high process air flow is
present at a temperature slightly
lower than the traditional aluminum
separator type ‘red silicone’ filter.
Filter efficiency ranges from 99.95
to 99.995% in accordance with EN1822 (IEST-RP-CC-001 Type E & K).
How rapidly can I heat up or cool
down a high temperature filter?
This common question is second
only to… ”Our filters have failed and
I need replacements by tomorrow”.
The official position of Camfil is to
default to the equipment provider.
It might seem like a dodge, but
experience tells us that no two
ovens/tunnels are the same. The
equipment provider has ‘validated’
how a specific filter has performed
in their specific equipment,
www.camfil.com
often re-labeling filters at higher
temperatures than may have
been recommended by the filter
manufacturer. This is okay; filter
manufacturers are a conservative
bunch. If the equipment
manufacturer is comfortable with
increasing the ramp-up rate and
pushing the temperature limit, that
is between them and the end user.
When pushed, Camfil recommends
(with no guarantees) that you not
exceed temperature change rates
greater than 100° F per hour or 1.6°
F per minute (55° C/hour or 0.9°
C /minute). The Termikfil, because
of its construction, is rated at a
temperature change rate of 212°
F per hour or 3.5° F per minute
(120° C/ hour or 2 ° C/minute).
Camfil Technical Bulletin
The Camfil Termikfil is pre-treated and prequalified with an exclusive heat preparation
cycle up to 300 c (572 F)
What is filter “burn-in?”
Filter burn-in is the initial tempering
procedure following the installation
of new filters into an oven. With
the exception of the Termikfil, as
this filter is ‘conditioned’ at 572°
F (300° C). This means that all of
the organic material used to bind
the filter media, and any other
residual organic material used in
the materials, are still present on
the filter. Additionally, if integrity
testing was performed after
installation, the test aerosol is also
captured in the filter media. These
materials must be removed by
thermal oxidation before placing the
oven into service. Final tempering
process on-site generates fumes
and odors that might contain
harmful or irritant compounds.
Combustion gases are mainly
carbon dioxide and water vapor. We
can have small quantities of carbon
monoxide and other substances
(MSDS available on request).
It is recommended to take steps, as
much as possible to lower exposure
to personnel, for example:
•
Avoid people present in the
vicinity during the conditioning
or burn-in process.
•
Run the exhaust system and
ensure good ventilation of the
room without recirculating the
air.
How long does a high temperature
HEPA filter last?
Filter life will depend upon the
operating conditions. Because these
filters are often operated under
very clean conditions, the common
HEPA filter recommendation to
replace the filter when the initial
pressure drop has doubled may
not apply to a high temperature
filter. Filters should be changed if
they are no longer able to maintain
the cleanliness of the air for the
process environment. Exceeding
the temperature limit, or heating
the filter more rapidly than
recommended may significantly
shorten filter life. That said,
Camfil’s experience has shown
that if the owner has a history of
pass/fail on periodic certifications,
High Temperature HEPA Air Filters FAQs
that operate in a “single pass”
mode and have only one chance
to remove particles, most process
ovens operate in a “multi-pass”
mode in order to avoid excessive
heat loss. This means that the air
entering the filter during steady
state operating conditions is very
clean. In these situations, assuming
the process does not generate
lots of particles, the presence of
a small pin-hole or small area of
penetration greater than average is
of little consequence to the overall
cleanliness of the process.
High temperature separator type
HEPA with Ceramic Construction
patterns of ‘failure’ can be
predicted based on the specific
site operation conditions in the
given tunnel or oven, a 3 to 5 year
life mostly based on certification
‘failure’ is a reasonable assumption.
What does the FDA say in relation
to leak testing?
The FDA states that among the
HEPA filters that should be leak
tested are those installed in ovens
and tunnels that are commonly
used to depyrogenate glass vials.
It is important to note that where
justified, alternate methods can be
used to test HEPA filters in the hot
zones of these tunnels and ovens.
Should we integrity-test high
temperature filters?
This is a very difficult question,
and this is where many people run
into problems with certain high
temperature filters. The purpose
of a high temperature filter is
to supply appropriately clean
air to the downstream process.
Unlike most clean room filters
www.camfil.com
In addition to visual inspection,
many operators elect to conduct
integrity testing after filter
installation and prior to filter
tempering to ensure there are
no large areas of damage from
handling or installation of the filter
media pack. Effective clamping can
also be evaluated, as the absence
of a seal on filter-to-hardware
mating surfaces can be detected.
After burn-in, the emphasis shifts to
particle testing of the environment
inside the oven downstream of
the filter during normal operating
conditions to ensure that the
desired cleanliness level is
achieved. Some certifiers have built
elaborate devices (an air or water
cooled ‘jacket’ for example) in
order to rapidly reduce temperature
so discrete particle counters can
function. It is important to apply
the ideal gas equation to determine
the actual count per cubic meter
of hot air. A sample of 1 cfm
would be approximately double at
650° F (343° C), so this needs to
be included in your calculations.
Particle losses can also occur due
to the extended length of sample
tubing required that is typically
longer than recommend in guidance
documentation. Those who later
elect to conduct integrity testing
Camfil Technical Bulletin
subsequent to filter burn-in and
operation may find that there are
areas of penetration around the
edges of the filter media pack
greater than 0.01%, while hot
particle testing showed acceptable
cleanliness levels in the process
environment. This finding does
not necessarily indicate a problem
with the high temperature filters.
In these situations, a decision to
keep or replace the filters based
on facility policy and procedures
needs to be made by the process
owner and quality assurance
department.
These responses pertain to filters
manufactured by Camfil only. It
should not be assumed that these
answers necessarily hold true for
products manufactured by other
companies.
High Temperature separator type
HEPA with Silicone Construction
Technical Bulletin
Life Science & Microelectronics
The table below outlines the performance of various
high temperature filters manufactured globally by Camfil.
High Temperature HEPA Filter Details Specific to Camfil
FRSI
6-½” (170 mm)
1FRSI-600
1FRSI-1000
FRK
6-½” (170 mm)
FRK-600
1FRK-1000
Solfilair
(high temp)
1506.23.04
Termikfil
6P6
K Series
(standard & high
capacity)
24” x 24” x 12”
(610 x 610 x 300 mm)
F Series
(standard & high
capacity)
24” x 24” x 12”
(610 x 610 x 300 mm)
Airflow for 24" by 24"
(292 by 292 mm)
730/1200 cfm
(1240/2038 m3/hr.)
730/1200 cfm
(1240/2038 m3/hr.)
1765 cfm
(2998 m3/hr.)
700 cfm
(1189 m3/hr.)
1040 cfm
(1766 m3/hr.)
1000 cfm
(1699 m3/hr.)
Efficiency
at Nominal Airflow
99.99% @ 0.3µ or
99.95% @ MPPS
99.99% @ 0.3µ or
99.95% @ MPPS
99.995% @ 0.3µ
99.99% @ 0.3µ
99.97% or
99.99% at 0.3µ
99.97% at 0.3µ
Pressure Drop
at Nominal Flow
1.0" w.g.
(250 Pa)
1.0” w.g.
(250 Pa)
1.1” w.g.
(273 Pa)
1.0” w.g.
(250 Pa)
1.0” w.g.
(250 Pa)
1.0” w.g.
(250 Pa)
Standard Frame
stainless steel
stainless steel
stainless steel
ceramic
304 stainless steel
304 stainless steel
6” & 11½”
(150, 300, & 90 mm)
6” & 11½”
(150 & 300 mm)
11½” (300 mm)
3.3” (84 mm)
6” &11½"
(150 & 300 mm)
11½" (300 mm)
fiberglass
fiberglass
silicon
rolled microfine
glass
silicon
aluminum & fiberglass
no gasket
no gasket
no gasket
no gasket
no gasket
no gasket
Silicone
ceramic
silicon
ceramic
silicon
ceramic
aluminum
aluminum
glass filament
glass filament
aluminum
aluminum
none
none
none
2 stainless
screens
none
1 304 stainless
steel screen
Media Type
microfine glass
microfine glass
microfine glass
microfine glass
microfine glass
microfine glass
Media Area 24” x 24”
(29.2 by 29.2 cm)
123/242 sq. ft.
(11/22 m2)
123/242 sq. ft.
(11/22 m2)
431 sq. ft.
(40 m2)
130 sq. ft.
(12 m2)
186 sq. ft.
(17 m2)
180 sq. ft.
(17 m2)
> 6” (150mm)
> 6” (150mm)
< 6” (150mm)
< 6” (150mm)
> 6” (150mm)
> 6” (150mm)
12
10
2
7
7
7
0.05%
0.05%
0.10%
0.01%
guaranteed
0.03% or 0.01%
guaranteed
0.03%
at 68°F (20° C),
thermal rise upon
installation
at 68°F (20° C),
thermal rise upon
installation
at 68°F (20° C)
600° F (315° C)
factory qualified
at 68°F (20° C),
thermal rise upon
installation
at 68°F (20° C),
thermal rise upon
installation
482° F (250° C)
662° F (350° C)
446° F (230° C)
662° F (350° C)
500° F (260° C)
750° F (398° C)
32 lbs. & 46 lbs.
(12 & 17 Kg)
32 lbs. & 46 lbs.
(12 & 17 Kg)
67 lbs.
(25 Kg)
13 lbs.
(5 Kg)
42 lbs.
(17 Kg)
59 lbs.
(22 Kg)
high
high
Frame Height
Standard Gasket
Alternate Gasket
Sealant
Standard Separator
Standard Face Grid (protective)
Pleat Height
Size Availability
(standard sizes)
Leak Rate (%)
Factory Test
Conditions
Maximum Operating
Temperature
Weight
Packaging
Mechanical
Resistance
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Camfil Absolute packaging
high
high
high
medium
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Performance & Features