hepa filter testing.pdf
TRANSCRIPT
4/5/12
1
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
San Diego, 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.
Photometer Probe - April 2012
4/5/12
2
San Diego, April 2012
IEST-RP-CC-034 For 11 years (1999 – 07/2010)
ISO 14644-3 2005 – Current. Address changes made after July 2010.
Photometer Probe - April 2012
San Diego, April 2012
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
Photometer Probe - April 2012
San Diego, April 2012
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
Photometer Probe - April 2012
4/5/12
3
San Diego, April 2012
Dp = Probe dimension parallel to scan Fa = Flow rate of photometer V = Average velocity of filter Wp = Probe dimension perpendicular to scan
direction
Photometer Probe - April 2012
Dp VWp
Fa=
San Diego, April 2012
HEPA has 90 FPM average velocity 1 CFM flow rate of the photometer Probe dimension perpendicular to scanning
direction = 3.2”
Photometer Probe - April 2012
Dp 90 fpm x 3.2"
1 ft minute=
3
Dp 1,080" minute x 3.2"
1728 in minute=
3
San Diego, April 2012
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”
Photometer Probe - April 2012
TL
4/5/12
4
San Diego, April 2012
Range of 5-8 Probes required when scanning HEPA Velocities From 32 fpm to 201fpm.
Photometer Probe - April 2012
San Diego, April 2012
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.
Photometer Probe - April 2012
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
San Diego, April 2012
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.
Photometer Probe - April 2012
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
4/5/12
5
San Diego, April 2012
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).
Photometer Probe - April 2012
San Diego, April 2012
Sr = Probe dimension parallel to scan Ar = Flow rate of photometer Wp = Probe dimension perpendicular to scan
direction
Photometer Probe - April 2012
Sr Wp
Ar=
San Diego, April 2012
Probe dimension perpendicular to scan direction = 3.2”
Photometer Probe - April 2012
Sr3.2"
21 ft minute=S
r3.2"
2144 in minute=
4/5/12
6
San Diego, April 2012
Sr = Linear scan rate (cm/sec.) Wp = Probe dimension perpendicular to scan
direction (cm)
Photometer Probe - April 2012
Sr Wp
15=
San Diego, April 2012
3.2” Probe dimension perpendicular to scan direction ( 8.128 cm)
Photometer Probe - April 2012
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
4/5/12
7
San Diego, April 2012
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.
Photometer Probe - April 2012
San Diego, April 2012
Pulls surrounding clean air
Captures 100% of particles coming through a defect
Photometer Probe - April 2012
San Diego, April 2012
Excess volume is forced outside of the probe.
Captures <100% of particles coming through a defect
Photometer Probe - April 2012
4/5/12
8
San Diego, April 2012
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.
Photometer Probe - April 2012
San Diego, April 2012
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)
Photometer Probe - April 2012
San Diego, April 2012
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.
Photometer Probe - April 2012
4/5/12
9
San Diego, April 2012
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.
Photometer Probe - April 2012
San Diego, April 2012
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.
Photometer Probe - April 2012
San Diego, April 2012
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
Photometer Probe - April 2012
4/5/12
10
San Diego, April 2012
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.
Photometer Probe - April 2012
QUESTIONS?
Photometer Probe - April 2012