HEPA Efficiency

GOOD ENGINEERING PRACTICE (cGEP)
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  1. In EN 1822 regarding HEPA Efficiency, There is Efficiency% @MPPS. In that what is the difference between Overall and Local Efficiency? How much %leakage shall be accepted? How can we define that % leakage?
  2. As far as my knowledge H13 filter should have 99.97% Efficiency. But EN 1822 Table i have not found 99.97 where as it has 99.95.

I am so confused.Please anyone can clear my doubts.

Thanks in advance…

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Hi

Don’t be confused, your job as a validation person is to validate the installation, which will be designed by persons well versed in HEPA filter usage, not to get involved in design.

Where room conditions are critical, it is required that not only should the filter efficiency be as specified, i.e. 99.97% efficient, but that there be no discernable point on the filter face, where the quality of the air is not within specification.

For instance;

You could have a filter where the filter material is working perfectly and the efficiency is almost 100%, but there is a pin hole through the filter media. Through this pin hole 0.02% of the total flow is flowing, completely unfiltered.

If you were checking the filter efficiency by taking measurements in the duct (mass flow) you would not see this leak, since the mass flow would still show 99.97% efficiency.

For this reason air flow into critical areas is tested by line scanning across the filter face. Which involves taking measurements along parallel lines across the filter length, about 25mm apart and 25mm away from the filter face, ensuring the complete face of the filter is scanned.

This way the filter core integrity is tested.

On the other hand exhaust filters are usually tested, by taking measurements across the airflow ducting.

The two tests are referred to as: Duct Flow Air Quality.
Filter Integrity.

Alex Kennedy