Filter Problem

[friartuck]

I have an in line filter rated at 99.999% (DOP)H14 grade which appears to be letting a lot of 0.5 micron particles through.

The filter is a well known (very well made) bit of kit and so we don't think it is a problem with this.

The filter is new, the system is new. The filter has a gasket seal and has been DOP tested. (I haven't seen the certificate yet, but I am told it passed)

Has anyone got any ideas?

The 0.5 micron count should be less than 3500 particles per 1m3 but we are getting 130000 or more.

We have 28 other terminal type filters that are fine and they have H14 filters in as well.

The manufacturer of the terminal HEPAs are different to the in line unit and the filters are from different sources (i.e. one from UK and the other from main land Europe)

Are all H14 filters the same grade or efficiency?

Any ideas folks?

Friar Tuck of Sherwood

 

[quark]

All H14 filters should have same efficiency. I would, first, suspect the filter and would like to have it DOP tested in my presence. 3500particles of 0.5micron size/m³ seems to be class 100. This requires a filtration area of atleast 95%. How many filters are there in this room? Why are you doubting only one filter?

Such high counts are not possible unless something is terribly bad. What is the application? Did you perceive proper airflow into the return risers? Is the DOP upstream port of the filter properly closed? What counts you are getting just below the filter face?

 

[friartuck]

Quark

The system has been specified by the client as 99.999% efficiency filters with 20-25 ac/hr.(No room classification has been requested-they seem to do things like that here)

I also feel that the 3500 particles requirement is class 100 also, but the client has only asked for 20-25ac/hr (They have a lot of these facilities on site such as tablet packing and pharmaceutical production) The figures we are getting imply a clean room of about 10000 rather than 100.

I think the same as you that the 3500 classification is class 100 which would require 95% plus ceiling coverage and an air change rate of perhaps 300 or so.We have only been asked to supply one or two grilles per room (in fact no quantity has been specified)

The room in question is served by an inline filter with just 2 supply grilles. Areas needing a high classificatiuon have laminar cabinets or fume cupboards installed . The room is classed as 'non-sterile manufacturing'.

My query is, why do I get full DOP passes and very low particle counts for the adjacent areas served by terminal filter (H14 filters in terminal boxes), but I get counts of 140000 at 0.5 microns in the room served by an in line box. (This too has an H14 filter)

I think there could be a pin hole. But would this I feel give higher counts at the larger particle sizes. We only get high counts at 0.5 down to 0.3 microns which seems like a duff filter or wrongly labelled filter perhaps??

I have had the ductwork cleaned and sterilised to make sure that the problem wasn't with dirty ducting, but this has not made any difference. So I am back to a poor filter etc.

Would a DOP test tell us if the filter was an H12 for example rather than an H14.? I'm not quite sure how the DOP test works, apart from forcing smoke into a duct and measuring the smoke level after the filter. We had results of 0.001% passing during the tests. (For the terminal units).
I am still awaiting the officiel test results for the in line unit, but I have been provisionally told that it too passed the DOP test.






Friar Tuck of Sherwood

 

[IRstuff]

Can you swap or otherwise replace the filter in question?

Are you sure that there isn't something in the room that's generating the spurious particulates?

TTFN

 

[quark]

Can you do full filter face scan with a DOP probe for this inline arrangement? Generally, downstream side of inline filters doesn't have full access and what we do is averaging. You will get erratic results if you are scanning the filter nearer to its face. Keep a distance of 1' and you may get better averaged results.

Particle generation rates for granulation, sifting, coating and compression areas are very high. If you didn't provide enough area of filtration and no. of ACPH, you will get higher counts in the area. If you take the particle readings nearer to the HEPA and if they are OK, then particles may be accumulating within the area and there is no enough cleaning.

Secondly, checking the particle counts at the air exit into the room will let you know any particle pickup in the duct work.

You can't designate a filter with DOP testing alone, for you may never come to know whether it's filter integrity or efficiency that is causing actual leakage. Generally, particle range from 0.1 to 0.4(you can also include 0.5)microns is called MPPS(most penetrating particle size) and the HEPA filter efficiency is very low in this range. On either side of the range it is very high. That is the reason why you get more counts in this range and low outside it.

If the filter is leaking and guarantee is void you can seal to a maximum limit of 5mm width by 1" length as per IES-CC-RP-006.

This link gives you some details about DOP testing.

http://www.c-vac.com/testing.html

Good luck,

 

[Longwinded]

Suggest that you review all operator and maintenance logs.

See if there is a trend.

Check to see that stray particulates are completely removed from the interior of the filter housing and associated piping.

Some filter housings are hard to keep clean.


good luck!

 

[friartuck]

Dear All Eng Tipsters

Thanks for the response

Thankfully ALL of the filters have passed now.

There appeared to be a manufacturing problems. The manufacturer replaced the filters FOC and did some work on the knife edges. I was amazed at how much of an effectthe slightest defect(And I mean microscopic defects) could have on the DOP readings.

Again, thanks for the input



Friar Tuck of Sherwood