[ RadSafe ] Air monitor question

[Wes Van Pelt]

John,

Isokinetic sampling has nothing to do with turbulent flow or mixing. It is
simply the matching of the linear velocity of the air in the duct with that
in the sampling probe so as to not select by particle size.  With a low duct
flow rate just reduce the flow rate in the sampling probe and sample for a
longer time. 

The other issue is representative sampling across the duct which is related
to turbulence and mixing. For this I would suggest installing a matrix of
sampling probes across the duct and combine the flows so as to get an
average concentration.

I would not recommend using a conservative "safety factor" for various
reasons.

Best regards,  Wes
Wesley R. Van Pelt, PhD, CIH, CHP 
Wesley R. Van Pelt Associates, Inc.  
 


-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of
JOHN.RICH at sargentlundy.com
Sent: Thursday, March 11, 2010 6:53 PM
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] Air monitor question

Radsafers

we have a plant vent monitor with the following problem: 

On occasion, the airflow is reduced to the point were there isn't enough 
to produce turbulent flow, mixing, or a velocity anywhere  near the that 
needed for isokinetic sampling. 

If anybody has had a similar situation, I'd like to discuss our proposed 
"fix" with you.  The thinking at the moment is to develop a conservative 
compensation factor that would be applied to the releases measured and 
recorded during these periods.  But there are could be hidden traps in 
this approach that will cause problems down the road.

thanx  in advance
 - - jmr


John Rich
312-269-3768
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