Re: Air-O-Cells

[Guest guest]

Absolutely

NOT. The Air-O-Cell (AOC) works by

impacting particles in a sticky medium.

Airflow through the cassette affects particle velocity. If the particles are moving too

quickly, some bounce off the surface and are carried away, and are not measured. If they are moving too slowly, the

particles will hit but not stick to the medium, will roll off and be carried

away, and again are not measured.

Therefore, adjusting the airflow through the cassette either way can lower

the final count on analysis.

The

flowrate can be monkeyed with a bit—I am not sure of the specific circumstances

under which the adjustment can be made, however—I would suspect that the

relative humidity of the incoming air would have something to do with

collection efficiency, but I am not sure.

A very respectable former employer of mine performed a small study to

determine optimum flowrate and settled on 12 Lpm. I think the study may have had flaws, but in any case, the

samples were collected in very dry air.

The end

result is: “Stray from manufacturer’s recommendations only in extreme

circumstances!”

A. Walsh MS, CIE

-----Original

Message-----

From: talk2ps@...

Sent: Friday, October 22, 2004

12:00 AM

To: iequality

Subject: Air-O-Cells

I have a question

for the group concerning the use of an Air-O-Cell® cassettes for fungal

bioaerosol air sampling under what would typically be considered normal post

remediation clearance conditions.

Are there any

circumstances where it would be necessary (or even advisable) to reduce the

airflow rate through the Air-O-Cell® cassette down to 5 liters per minute and

to increase the run time on the pump to 15 minutes in an " open air "

condition (be it in an indoor/outdoor situation)?

It would appear to me

that, since Zefon publicly states that the optimum efficiency of their The

Air-O-Cell® cassette lies at an airflow flow rate that begins at a minimum of

15 lpm, that reducing that airflow rate by threefold (down to 5 lpm) would

cause an Air-O-Cell® to miss many of the smaller and lighter weight

particles/spores (who’s low mass and reduced velocity into the trap would

not be capable of causing an adherent collision with the sticky trace area

of the slide?

Any opinions on this

would be most welcome. Also, if you do sometimes change the flow rate on

Air-O-Cells beyond the parameters that the manufacturer stipulates in its

literature, why do you do so and what other flow rates do you use?

[Guest guest]

No. Changing the air flow rate will negate the laboratory's ability

to read the sample. The labs use the standard operating procedures

designed by the manufacturer to determine the correct equation to use

during analysis. Any change to the SOP will throw off the ability to

accurately determine the ppm concentration of the spores.

The Air-O-Cell cassette's jet-to-plate ratio will only capture spores

and conidia larger than 2.5 microns. While this will capture

particles from the dreaded Stachybotrys chartarum (aka " Black Mold " )

it does have the potential to give false negatives for

several " Indicator Species " that have spores smaller than 2.5 microns.

The best thing to do in your case may be to use a viable sampler like

the A-6 or, if you need a faster turn around from your lab,

use the Micro5 Microcell. The jet-to-plate ration on that casstte is

small enough to capture a wider range of fungal spores, bacterium and

even anthrax.

[Guest guest]

Thanks Jeff,

Your response makes total sense to me and thanks to everyone else who has responded up to this point as well. I am still researching information on this topic so I want everyone on the IEQ forum to feel free to continue to give me their comments and opinions even though my initial question seems to have been answered.

Let me explain myself a bit further so that people don't get the wrong impression...

I am not at all considering running any of my own Air-O-Cell® samples at 5 lpm. Someone else has apparently done Air-O-Cells® samples at 5 lpm to pass post remediation clearance on a project that I had previously failed (due to high levels of Aspergillus/Penicillium) in both viable (single stage plates) and non-viable (Air-O-Cell® cassette) samples.

His report documentation (that I have been asked to review prior to litigation) reported the 5 lpm flow rate and a run time of 15 minuets on the Air-O-Cells® samples taken. Needless to say, that was a MAJOR red flag for me. Just some of the ‘organisms of concern’ during this project were the small (low mass Asp/Pen) spores that would certainly be miscounted on an Air-O-Cell® trace when the sample was drawn at a flow rate of 5 lpm (this is according to the manufacturer’s own documentation).

I consider myself to be proficient in sample taking as well as interpretation of the resulting lab reports and I was truly taken aback by the clearance report and documentation delivered by this well credentialed individual (albeit his credentials/expertise is not necessarily related to bioaerosol sampling).

All of the professional information and feedback that I have thus far received validates my original thinking on this matter. That being; that the efficiency of any "inertial particle impactor" is based primarily on the incoming velocity of the particulate matter and the designed ability of the impactor to retain those targeted particles incoming at that given velocity. In other words its all about the "cut point" of the given air sampling device.

In regard to the Air-O-Cell® cassettes, it is my understanding that the optimum incoming particulate velocity is directly related to the airflow velocity delivered through the impactor device by the pump. This has been well established by the manufacturer (Zefon International) to be 15 liters per minute (lpm) based on the mass of the typically targeted fungal particulates/spores and the optimum collection design characteristics of an un-expired Zefon Air-O-Cell® cassette. The concurring data (offered by Zefon International) appears to be based on the March 27th, 1998 Willeke document regarding Particle cut-size evaluations relating to the Air-O-Cell® Sampler.

It would seem to me, therefore, that those who would deviate from Zefon’s usage specifications (in regard to airflow rates through the impactor) do so at their own peril in our litigious society.

Phil S.

------------------------------------------------------------------------

From: Jeff Mantz

To: iequality

Sent: Friday, October 22, 2004 1:28 PM

Subject: Re: Air-O-Cells

First, I can't think of a single reason why you would want to even attempt to use the Air-O-Cell® cassette at a flow rate of 5 LPM. Why would you be considering this?

Second, what will happen if you do sample at 5LPM? Basically the efficiency will change and you will collect less particles in lower size ranges. Consequently, if you raise the flow rate you will collect more smaller particles. Once you hit higher flow rates, larger particles will begin to "bounce" and the collection efficiency of them will be reduced. Thus 15LPM rate provides you with the best balance of large and small particle collection.

Regards,

Jeff Mantz

Zefon International

--------------------------------------------------------------------talk2ps@... wrote:

I have a question for the group concerning the use of an Air-O-Cell® cassettes for fungal bioaerosol air sampling under what would typically be considered normal post remediation clearance conditions.

Are there any circumstances where it would be necessary (or even advisable) to reduce the airflow rate through the Air-O-Cell® cassette down to 5 liters per minute and to increase the run time on the pump to 15 minutes in an "open air" condition (be it in an indoor/outdoor situation)?

It would appear to me that, since Zefon publicly states that the optimum efficiency of their The Air-O-Cell® cassette lies at an airflow flow rate that begins at a minimum of 15 lpm, that reducing that airflow rate by threefold (down to 5 lpm) would cause an Air-O-Cell® to miss many of the smaller and lighter weight particles/spores (who’s low mass and reduced velocity into the trap would not be capable of causing an adherent collision with the sticky trace area of the slide?

Any opinions on this would be most welcome. Also, if you do sometimes change the flow rate on Air-O-Cells beyond the parameters that the manufacturer stipulates in its literature, why do you do so and what other flow rates do you use?

Phil S.

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