HEPA Test 1

[SAK9]

Guys,

I am designing a lab facility with HEPA filters mounted as ceiling exhaust terminals.If I need to do a DOP test at 100 % airflow on the exhaust HEPA filter,what is the best arrangement to do it? Do I need to place some sort of a chamber below the filter to inject the DOP keeping the other end open for air to flow in?I would appreciate some input from some one who has done it before.
Thanks for your help

 

[quark]

We generally charge DOP at each filter face independantly. But the chamber idea seems to be good. But I couldn't understand what did it mean by keeping the other end open for air to flow in. Do you mean to open the ducting dropper so that you can probe for penetration? If so, that should be the thing you have to do. But try to cover the filter from the 4 sides.

Just out of curiosity, what is the area classification? Generally whenever you have HEPA out to trap containment, it is preferred to have return from bottom of the controlled area.

 

[SAK9]

Quark,

Thanks for your post .The application is for is a BSL-3 lab.My idea is to use a chamber which has the same dimensions as the filter face for the test.Through a port on one side of the chamber, the DOP vapour can be released into the chamber.One open end of the chamber would butt against the filter face whereas the opposite open end would allow the filter to draw air from the room.This would enable testing the filter at 100% air flow using the system fan.

As for measuring the count downstream of the filter,I intend to provide one more port for inserting the particle count probe.Do you think such an arrangement will give satisfactory test results?

 

[wilg]

We use returns that are close to the floor,
ceiling mounted returns for BSL-3 lab seem
like a strange configuration. Disaassociation
of laminar flow would occur below the supply
HEPA's. We measure laminar flow below the supplies
at X distance. Use of a chamber seems interesting.
wilg5404@aol.com

 

[quark]

Actually checking should be done by sweeping the probe across entire cross section of the filter to check actual position of the leakage. If you just put the probe at a suitable place, you will get average penetration and this will lead to the masking of actual problem.

Authorities still use IES-CC-RP-006 as a reference for integrity test of HEPA filters and that document regulates the maximum leakage area(5mmx12mm) that can be sealed using silicone sealant.

For general operation, checking the average penetration is ok. But if you are going to face the regulatory audits, just be prepared with the above questions.

Actually I, long back, discussed this issue with one of our UK consultants but yet to get an answer. I will let you know as soon as I get some information.

Regards,

 

[wilg]

Mil-Std-282 is recognized as the standard for "hot" DOP efficiency testing and is used for compliance with many HEPA filter specifications. It is also recognized as being
"monodisperse 0.3 micron particles" as referenced in EPA and OSHA definitions for HEPA filters.

"Cold" DOP has a broad particle size with larger average size than "hot" DOP. Efficiencies are, therefore, higher with "cold" DOP than with "hot" DOP. The control of temperatures and flow rates with the equipment is critical to maintaining a consistently tight particle distribution which allows for consistent and reproducible efficiency measurements
Where "cold" DOP can be useful in determining HEPA filter efficiency is when testing in accordance with IEST-RP-CC007.1. For each test, particle counters are calibrated to simulaneously count the number of 0.3 micron particles both upstream and downstream of the filter. Providing the "cold" DOP challange aerosol contains a statistically significant number of 0.3 particles, the inefficiency or penetration in percent can determined. In this test, the polydisperse nature of "cold" DOP is irrelavent because the other particle sizes are not measured.
wilg5404@aol.com

 

[lilliput1]

Contact the HEPA filter housing manufacturer & see what they can provide.

 

[SAK9]

Wilg,
Thanks for posting that very useful graph comparing the two test methods.

Quark,

How can we scan an exhaust HEPA filter as the clean side is inside the duct?You may need an access door to do this?But when you have an access door, air will be pulled through the access door and flow through the exhaust filter may drop well below the 100% flow.Any solutions to overcome this?

 

[quark]

The latest document which covers the testing of cleanrooms is ISO 14644-3 (voting on draft copy was supposed to be done in March, 2003), which guides to maintain a flow rate within +/-30% of the actual flow. But the sampling method should be isokinetic. Actually feed rate of the probe should be maintained to have isokinetic sampling.

It further says, particle measurement can be done in duct work when penetration of particulate penetration is more than 0.005% of the MPPS. If you have EU-12 HEPA(99.97%) then you can make the measurement in the ducting. If you are using better filters then the particles should be checked at a distance not more than 6" from the filter face.

The concentration of upstream aerosol should be between 10 to 100 mg/M³, but better result will be in the range of 20 to 80 mg/M³. The ratio of maximum to minimum concentration of test aerosol over a period of time should be not more than 2:1 at any point.

As Wilg rightly suggested, you should calibrate upstream concentration every time you check any filter. You should provide a port to check this.

The reason for not measuring every particle size during integrity testing filters is as below.

When you check typical efficiency curve of a HEPA filter, the highest penetration will be between 0.5 micron and 0.1 micron (infact it is a parabola). Efficiency below and above this range of particles is high. Particles in this range are called MPPS (Most Penetrating Particle Size). So an average size of 0.3 micron is considered in this range presuming that, if we control MPPS within required limit all other particle sizes can also be controlled.

Regards,