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Monday, August 11, 2014

Exposure Modeling Data Base Needs


Quite a few years ago, Neil Hawkins and I wrote a few papers about the potential value of exposure modeling to the Industrial Hygiene community.   For those of you who know Neil, he is a very bright, creative and well-organized individual with an abundance of managerial acumen.  In short, he is great collaborator.  More important, we shared a belief in the utility of modeling.  In Neil’s case he had a vision of what needed to happen for the science to move forward.   I was in the weeds working on the details of the models while he was in the clouds looking at the big picture.  He started talking with me about the awareness and changes that needed to happen in the IH community in how we do our jobs in order for modeling to really take hold.

Indeed, if you want or need to evaluate an exposure you have essentially two ways to approach its assessment.  The first is very direct and the manner in which many of us were taught in school.  You measure the exposure directly and then compare that exposure to some toxicological benchmark.  To do this you needed a methodology and sampling protocol.

The other method, the method we were advocating in those days, was to conduct a model estimation of the exposure.   To do that you needed a model which had the following general form:

Predicted Exposure = f (the factors that caused the exposure)

Thus, your model always needed to be “fed” with the factors or values of the variables that were driving the exposure. 

Surprisingly, at least to me at the time, was the fact that most of the factors that were needed to feed our models were not commonly available.   The very entities that were driving the exposures to occur were not being captured and studied.  

This is not to say that there was not any exposure assessment data available.  Indeed, there were literally hundreds of thousands of measured exposures, typically breathing zone concentrations measurements in workers' breathing zone, in various databases.  Unfortunately, they were not particularly useful to the development of models which we believe represents the most basic element of the science of exposure assessment.    That is, they provided the left-hand side of the above equation but not the determinants of exposure on the right hand side.

As such, we set about to outline the data needs that would ultimately feed the modeling and exposure assessment process.  This resulted in Neil and I putting out the following paper which is now almost 20 years old:

Exposure Database Improvements for Indoor Air Model Validation

         APPL. OCCUP.ENVIRON.HYG. 10(4), APRIL 1995


I will be happy to send you a copy of this paper if you request it from me: mjayjock@gmail.com
Some of the bullets from this work are presented below.

We identified some “big picture” exposure determinants in need of capture
·         Source Characterization
·         Time Course
·         Sinks
·         Ventilation and Dispersion

To bring it down to earth in an operational scene, we proposed constructing a check-list for capturing the following minimal information in exposure databases to go along with the measured exposure:
·         source characteristics
·         areas and types of sinks
·         general type of building
·         room dimensions
·         qualitative ranking of smoke dissipation
·         assessment of equilibrium

I am sad to say that this idea never really caught on and, for the most part, we are still not capturing these determinants of exposure concurrently with our breathing zone monitoring data. 

Questions for discussion in the LinkedIn Groups:

Am I wrong?  Is there anything like this going on in your organization?
Why do you think this never got any traction?
Would you like to see such data captured and paired to monitoring data?


3 comments:

  1. I think it never gained traction for several reasons. 1) I think many in our field are not fond of using math, maybe some do not trust models but I think more do not feel comfortable doing the same math they used daily in college. 2) It is too easy to run out and monitor someone. 3) Our bosses trust hard data from exposure assessments more than our ability to manipulate equations. 4) OSHA emphasizes hard numbers from personal monitoring and downplays, or even ignores, area investigations. 5) There has been precious little pairing of data from model predictions and exposure assessments and where available there is often a huge gap between prediction and reality leading to mistrust by the unenlightened. 6) Yes we need to capture more data because the final reason, I believe, is lack of data for the "other" factors.

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  2. Pertti (Bert) HakkinenAugust 11, 2014 at 3:05 PM

    Hi Mike. Excellent blog post. In a future post, you might want to take a look at this topic relative to assessing consumer product-related exposures. One publication to consider if you look at the consumer product-related side is:
    "Issues in consumer exposure modeling: towards harmonization on a global scale."
    http://www.ncbi.nlm.nih.gov/pubmed/17668010
    As I recall, you were at the workshop that led some of the participants to write this manuscript.

    (Disclaimer: Statements above are my personal opinion.)

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  3. I am an OSHA IH. Before OSHA, I was an Air Force Bioenvironmental Engineer (BEE). About 1990, there was a reserve BEE in New Jersey who developed what I thought was an outstanding model to predict, based on 3 or more air samples in a workplace, what the contaminant concentrations would be throughout the room. Regretfully, I did not have the computer resources to use his model. Reasons for this idea not catching up, as I see it, maybe (1) industrial hygienists, especially 20 years ago, not having the right computers/software/training to use this; (2) requiring too many assumptions to make the equations work, which may not hold in court. OSHA requires personal air sampling in its substance-specific standards to prove compliance. However, a model like this can be used to design a sampling strategy by anticipating what and where exposures in a workplace could be. I feel that you should continue to develop these models but stress that it will be a screening tool, not a substitute for actual personal breathing zone air sampling.

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