Hepa filters

Dear sir,

        What is the minimum velocity and maximum velocity for a hepa filter.

Dear Venkat

The recommended air velocity for the cleanrooms is 0.36 m/s - 0.45 m/s from the HEPA filters . And for the HEPA filters , the manufacturer normally identifies the minimum and maximum holding velocities for air in the area . you can visit the MSDS of HEPA filters by Camfil , Trox and AAF .


What should be the maximum allowable lenght for the connecting tube of a remote sensing particle (non-viable) counting device?
Because more the length of tube means more loss of particles.:mad:

Dear Sambhu,

Particle counters with as short a length of tubing as possible should be used to minimise the loss of ≥5.0 micron particles, the transit tube length should not exceed the manufacturer’s recommended length.”


Dear Shahnawaz

Thanks for your reply.
One more thing. Let me explain the conditios first:-

(1) Monitoring of cleanroom of Grade A (as per EU standard).
(2) Manned / unmanned conditions the limit (non viable particles) is 1/cube meter of 5 mocron or larger.
(3) Type of Particle counter: DPC light scattering, sampling capacity: 50 lit/min.
(4) Method followed: ISO 14644.

By considering above conditions, individual sample volume is required to be of 20,000 Lit., that means more than 6 hr. is required to take one sample. Practically it is becomming a time consuming & hectic too.
What should be the right option in this case? Can we go for Sequential Sampling Method?

Dear Sambhu,
First thing is that the sequential sampling procedure is only aplicable to sampling aimed at a total of 20 particles per measurement, for particles of the considered size at the specified class or concentration limit.
The limts define 1 cubic feet of air conatain less than 1 particle of 5 micron. But for 1 cubic feet of air sample, your equipment will take 20 min for one samples, which is not reasonable and not practicable, so i suggest that you may take 283litres of air for each sample. b/c 6 hours / one sample is not logically possible.

Thanks and best regards,

Dear Shahnawaz

Thank you very much for your reply.
I got final solution from your mail & proposed amendment of EMEA.
The EU standard has been revised by stating that in cleanroom grade A the maximum permitted number of particles at >= 5.0 micron can be upto 20/cubic meter (considering false counts).
By that way each sample volume will be of 1000 liters. That means our particle counter is able to collect that quantity of air within 20 min., which is practically possible.
Meet you soon…bye

Is there any guidance related to continuous non viable particle monitoring in specified areas like ISO Class 5, 6, 7 & 8. If any information related about the same, pl. provide us.

Please go through USFDA, MHRA guidelines on Sterile Products.

With Best Regards,
Sudarshan Reddy

:)Dear PVal

Guidance regarding standards of pharma Cleanrooms (both viable & non viable particle counts) are available in the guidance of EU, USFDA-CDER, MCC, ANVISA as well as Schedule M too. But the methods are only mentioned in ISO 14644-1, 2 and 3 documents.
FS 209E also indicates the methods but is it no more in existance (after 1999).
Continuous nonviable particle counting is no where mandatory (monitoring in scheduled intervals is mandatory) but it is recomended as per cGMP guidance of USFDA.
If you want the methods & standards of ISO 14644, I can give you personally.

What is Size of HEPA Filter

Al- Pharao Air Data

Annex 1 states that the veocity should be 0.45m/s + or - 20%. The actual statement is as follows;

“The local zone for high risk operation, e.g. filling zone, stopper bowls, open ampoules and vials, making aseptic connections. Normally such conditions are provided by a laminar flow work station. Laminar air flow systems should provide a homogeneous air speed of 0.45m/s +or- 20% (guidance value) at the working position.”