hepa filter testing.pdf

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What you thought you knew Patrick Law

San Diego, April 2012

  Two industry standards contain procedures for calculating the correct probe size to use when scanning HEPA/ULPA Filters.

  The same two also contain calculations for conducting your scan rate. ◦  IEST-RP-CC-034 ◦  ISO 14644 Part 3

  IEST RP’s 006 & 002 point you back to RP-034.

Photometer Probe - April 2012


  Pre 1999 - IEST-RP-CC-006 – A few pages dedicated to leak testing one probe size and one speed.

  1999 IEST RP-CC-034 - 40 pages dedicated to leak testing only. Multiple Probe sizes & Multiple speeds.

  2005 – ISO 14644-3- Very similar to RP-34 including Multiple Probes & Multiple speeds.

  July 2010 – IEST-RP-CC-034.3 (second printing) Quick fix with an annex taking us back to one probe, one speed.


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  IEST-RP-CC-034 For 11 years (1999 – 07/2010)

  ISO 14644-3 2005 – Current.   Address changes made after July 2010.



  Verify Airflow is operating within design limits.

  Direct read or calculate average velocity at each HEPA.

  Decide ◦  type & size of probe to be used ◦  Speed at which you will be scanning



  Somewhat Isokenitic sampling (± 10-20% of Average velocity.) ◦  Measurement or Calculation of exit velocity

  Scanning probe dimensions   Need to Calculate scan rate based on probe

dimensions


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  Dp = Probe dimension parallel to scan   Fa = Flow rate of photometer   V = Average velocity of filter   Wp = Probe dimension perpendicular to scan

direction


Dp VWp

Fa=


  HEPA has 90 FPM average velocity   1 CFM flow rate of the photometer   Probe dimension perpendicular to scanning

direction = 3.2”


Dp 90 fpm x 3.2"

1 ft minute=

3

Dp 1,080" minute x 3.2"

1728 in minute=

3


  The transition section of the probe should have an overall length, TL at least equal to the maximum dimension of the probe inlet Wp

  Dp ≥ 0.25”


TL

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  Range of 5-8 Probes required when scanning HEPA Velocities From 32 fpm to 201fpm.



  Since this standard requires the inlet velocity of the probe to be within ± 10% of the average HEPA velocity, multiple probes have to be owned.


Average Less Plus Probe Probe Inlet Velocity 10% 10% Wp (Inch) Dp (inch) Area (Sq. In.)

60 54 66 4.8 0.5 2.4 74 66.6 81.4 3.9 0.5 1.95 90 81 99 3.2 0.5 1.6

110 99 121 2.6 0.5 1.3 135 121.5 148.5 2.1 0.5 1.05 165 148.5 181.5 1.7 0.5 0.85


  Since this standard requires the inlet velocity of the probe to be within ± 20% of the average HEPA velocity, multiple probes have to be owned.


Average Less Plus Probe Probe Inlet

Velocity 20% 20% Wp

(inches) Dp

(inches) Area

(Sq.In.)

40 32 48 7.2 0.5 3.6 60 48 72 4.8 0.5 2.4 90 72 108 3.2 0.5 1.6

112 89.6 134.4 2.6 0.5 1.3 168 134.4 201.6 1.7 0.5 0.9

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  The maximum scan rate when using a square probe should not exceed 3 m/min (5 cm/sec) (10 ft/min or 2 in./sec).

  With a rectangular probe, the maximum area scan rate should not exceed 0.093 m2/min (1.0 ft2/min).



Sr = Probe dimension parallel to scan   Ar = Flow rate of photometer   Wp = Probe dimension perpendicular to scan

direction


Sr Wp

Ar=


  Probe dimension perpendicular to scan direction = 3.2”


Sr3.2"

21 ft minute=S

r3.2"

2144 in minute=

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  Sr = Linear scan rate (cm/sec.)   Wp = Probe dimension perpendicular to scan

direction (cm)


Sr Wp

15=


  3.2” Probe dimension perpendicular to scan direction ( 8.128 cm)


Sr 8.128 cm

15=

San Diego, April 2012 Photometer Probe - April 2012

0.5 0.62

0.75 0.92

1.14 1.41

2

0 0.5 1 1.5 2 2.5

60 fpm 74 fpm 90 fpm

110 fpm 135 fpm 165 fpm

Used to be

Scan Rate in Inch’s Per Second

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Velocity of the air exiting filter…

Matches the capture velocity of the air at the inlet of the probe.

Captures 100% of particles coming through the defect.



Pulls surrounding clean air

Captures 100% of particles coming through a defect



Excess volume is forced outside of the probe.

Captures <100% of particles coming through a defect


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  Current probe captures at 90 fpm.?   A filter with an average velocity of 135 fpm

could spill 1/3 of the particles outside of the probe area, under sizing the leak and making it harder to detect.

  A probe with an inlet capture velocity of 135 would be best.

  You could block off the current probe to increase velocity.



  Annex J   The rate at which the filter is scanned should

not exceed 10’ minute (0.05m/sec)   Use Probe provided by manufacturer unless

otherwise specified.   There still remains some confusion in section

6.2 (Installation Test)



  10.11.2.10   The rate at which the filter is scanned should

not exceed 10’ minute (0.05m/sec) if average velocity of HEPA is 90-110 fpm.

  If velocities are significantly higher, calculate scan rate per IEST RP-034.


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  IEST – Talks and sub-committees have been formed to evaluate the scan rate.

  ISO 14644 is due to be revised and talk is that it will have a change as well.



  How has the industry conducted this test method?

  Truth be told, most of us scan faster than 10’/min and still find leaks. ◦  However…..

  Solution is to have a method that is meaningful, reliable yet easy enough to conduct as a field test.



  Obtain current and new standards when they are released.

  Obtain draft standards and comment   Read and understand these standards when

they are published   Question what you don’t understand   Get involved in IEST or other industries that

are writing standards


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  The world will continue to scan filters as fast as they do with the supplied probe until there is a need to change.

  Our industry as well as our clients have ignored this method.

  IEST and/or ISO will likely publish a revision and if practical enough, it will be embraced.


QUESTIONS?


hepa filter testing.pdf

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